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+ANATOMY
+AY’S
+FOR STUDENTS Fourth Edition
+
+Richard L. Drake, PhD, FAAA Director of Anatomy
+Professor of Surgery
+Cleveland Clinic Lerner College of Medicine Case Western Reserve University
+Cleveland, Ohio
+
+A. Wayne Vogl, PhD, FAAA Professor of Anatomy and Cell Biology Department of Cellular and Physiological Sciences Faculty of Medicine
+GR
+University of British Columbia Vancouver, British Columbia, Canada
+
+Adam W. M. Mitchell, MB BS, FRCS, FRCR Consultant Radiologist
+Director of Radiology Fortius Clinic
+London, United Kingdom
+
+Illustrations by
+Richard Tibbitts and Paul Richardson
+
+Photographs by Ansell Horn
+
+
+GRAY’S ANATOMY FOR STUDENTS, FOURTH EDITION
+
+Copyright © 2020 Elsevier Inc.
+
+ISBN:      978-0-323-39304-1 IE ISBN: 978-0-323-61104-6
+
+
+All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies, and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).
+
+Previous editions copyrighted 2014, 2010, 2005 by Churchill Livingstone, an imprint of Elsevier Inc.
+
+
+
+Notices
+
+Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. With respect to any drug or pharmaceutical products identified, readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose or formula, the method and duration of administration, and contraindications. It is the responsibility of practitioners, relying on their own experience and knowledge of their patients, to make diagnoses, to determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.
+The Publisher
+
+
+Library of Congress Control Number: 2018952008
+
+
+
+
+
+
+
+
+
+
+
+
+Senior Content Strategist: Jeremy Bowes Director, Content Development: Rebecca Gruliow Publishing Services Manager: Catherine Jackson Senior Project Manager: John Casey
+Senior Book Designer: Amy Buxton
+
+Printed in Canada
+
+9    8    7    6    5    4    3    2    1
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+
+1600 John F. Kennedy Blvd. Ste. 1600
+Philadelphia, PA 19103-2899
+The Body
+
+
+What is anatomy?
+
+
+Anatomy includes those structures that can be seen grossly (without the aid of  magnification) and microscopically (with the aid of magnification). Typically, when used by itself, the term anatomytends to mean gross or macroscopic
+
+are studied at the same time. For example, if the thorax is  to  be  studied,  all  of  its  structures  are  examined. This includes the vasculature, the nerves, the bones, the  muscles,  and  all  other  structures  and  organs
+
+anatomy—that is, the study of structures that can be seen	located  in  the  region  of   the  body  defined  as  the
+
+without using a microscopic. Microscopic anatomy, also called histology, is the study of cells and tissues using a microscope.
+Anatomy forms the basis for the practice of medicine. Anatomy leads the physician toward an understanding of a patient’s disease, whether he or she is carrying out a physical examination or using the most advanced imaging techniques. Anatomy is also important for dentists, chiro-practors, physical therapists, and all others involved in any aspect of patient treatment that begins with an analysis of clinical signs. The ability to interpret a clinical observation correctly is therefore the endpoint of a sound anatomical understanding.
+Observation and visualization are the primary tech-niques a student should use to learn anatomy. Anatomy is much more than just memorization of  lists of  names.
+
+thorax. After studying this region, the other regions of the body (i.e., the abdomen, pelvis, lower limb, upper limb, back, head, and neck) are studied in a similar fashion.
+■     In contrast, in a systemic approach, each system of the body is studied and followed throughout the entire body. For example, a study of the cardiovascular system looks at the heart and all of the blood vessels in the body. When this is completed, the nervous system (brain, spinal cord, and all the nerves) might be examined in detail. This approach continues for the whole body until every system, including the nervous, skeletal, muscular, gastrointestinal, respiratory, lymphatic, and reproduc-tive systems, has been studied.
+
+Each of these approaches has benefits and deficiencies.
+
+
+
+Although  the  language  of  anatomy  is  important,  the network of information needed to visualize the position of physical structures in a patient goes far beyond simple memorization. Knowing the names of the various branches of the external carotid artery is not the same as being able to visualize the course of the lingual artery from its origin in the neck to its termination in the tongue. Similarly, understanding the organization of the soft palate, how it is related to the oral and nasal cavities, and how it moves during swallowing is very different from being able to recite the names of its individual muscles and nerves. An under-standing of  anatomy requires an understanding of  the context in which the terminology can be remembered.
+
+
+How can gross anatomy be studied?
+The term anatomy is derived from the Greek word temnein, meaning “to cut.” Clearly, therefore, the study of anatomy is linked, at its root, to dissection, although dissection of cadavers by students is now augmented, or even in some cases replaced, by viewing prosected (previously dissected) material and plastic models, or using computer teaching modules and other learning aids.
+Anatomy can be studied following either a regional or a systemic approach.
+
+The regional approach works very well if  the anatomy course involves cadaver dissection but falls short when it comes to understanding the continuity of  an entire system  throughout  the  body.  Similarly,  the  systemic approach fosters an understanding of  an entire system throughout the body, but it is very difficult to coordinate this directly with a cadaver dissection or to acquire suffi-cient detail.
+
+
+Important anatomical terms The anatomical position
+The anatomical position is the standard reference position of the body used to describe the location of structures (Fig. 1.1). The body is in the anatomical position when standing upright with feet together, hands by the side and face looking forward. The mouth is closed and the facial expres-sion is neutral. The rim of bone under the eyes is in the same horizontal plane as the top of  the opening to the ear, and the eyes are open and focused on something in the distance. The palms of the hands face forward with the fingers straight and together and with the pad of the thumb turned  90°  to  the  pads  of  the  fingers. The  toes  point forward.
+
+Anatomical planes
+
+
+
+■     With a regional approach, each region of  the body 2	is  studied  separately  and  all  aspects  of  that  region
+
+Three major groups of planes pass through the body in the anatomical position (Fig. 1.1).
+What Is Anatomy  •  Important Anatomical Terms	1
+
+
+
+Superior
+
+Coronal plane
+Inferior margin of orbit level with top of external auditory meatus
+
+
+Face looking forward
+
+Sagittal plane
+
+
+
+
+
+
+
+
+
+Anterior	Posterior
+
+
+
+
+
+
+Medial
+Transverse, horizontal, or axial plane
+Hands by sides palms forward
+
+Lateral
+
+
+
+
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+
+Feet together toes forward
+
+
+
+
+
+
+
+
+Inferior
+
+
+Fig. 1.1  The anatomical position, planes, and terms of location and orientation.
+
+3
+The Body
+
+
+
+■     Coronal planes are oriented vertically and divide the body into anterior and posterior parts.
+■     Sagittal planes also are oriented vertically but are at right angles to the coronal planes and divide the body into right and left parts. The plane that passes through the center of the body dividing it into equal right and left halves is termed the median sagittal plane.
+■     Transverse, horizontal, or axial planes divide the body into superior and inferior parts.
+
+■     Proximal and distal are used with reference to being closer to or farther from a structure’s origin, particu-larly in the limbs. For example, the hand is distal to the elbow  joint.  The  glenohumeral  joint  is  proximal  to the elbow joint. These terms are also used to describe the relative positions of branches along the course of linear structures, such as airways, vessels, and nerves. For example, distal branches occur farther away toward the ends of  the system, whereas proximal branches
+
+
+Terms to describe location
+Anterior (ventral) and posterior (dorsal), medial and lateral, superior and inferior
+Three major pairs of terms are used to describe the location of structures relative to the body as a whole or to other structures (Fig. 1.1).
+
+occur closer to and toward the origin of the system.
+■     Cranial (toward the head) and caudal (toward the tail) are sometimes used instead of  superior and inferior, respectively.
+■     Rostral is used, particularly in the head, to describe the position of a structure with reference to the nose. For example, the forebrain is rostral to the hindbrain.
+
+
+
+■     Anterior  (or  ventral)  and  posterior  (or  dorsal) describe the position of structures relative to the “front” and “back” of  the body. For example, the nose is an anterior  (ventral)  structure,  whereas  the  vertebral column is a posterior (dorsal) structure. Also, the nose is anterior to the ears and the vertebral column is pos-terior to the sternum.
+■     Medial and lateral describe the position of structures relative to the median sagittal plane and the sides of the body. For example, the thumb is lateral to the little finger. The nose is in the median sagittal plane and is medial to the eyes, which are in turn medial to the external ears.
+■     Superior and inferior describe structures in reference to the vertical axis of the body. For example, the head is superior to the shoulders and the knee joint is inferior to the hip joint.
+
+Superficial and deep
+Two other terms used to describe the position of structures in the body are superficial and deep. These terms are used to describe the relative positions of  two structures with respect to the surface of the body. For example, the sternum is superficial to the heart, and the stomach is deep to the abdominal wall.
+Superficial and deep can also be used in a more absolute fashion to define two major regions of the body. The super-ficial region of the body is external to the outer layer of deep fascia. Deep structures are enclosed by this layer. Structures in the superficial region of the body include the skin, superficial fascia, and mammary glands. Deep struc-tures include most skeletal muscles and viscera. Superficial wounds are external to the outer layer of  deep fascia, whereas deep wounds penetrate through it.
+
+
+Proximal and distal, cranial and caudal, and rostral
+
+Other terms used to describe positions include proximal and distal, cranial and caudal, and rostral.
+
+
+
+
+
+
+
+
+
+
+
+
+
+4
+Imaging  •  Diagnostic Imaging Techniques	1
+
+
+
+Imaging
+Diagnostic imaging techniques
+In 1895 Wilhelm Roentgen used the X-rays from a cathode ray tube to expose a photographic plate and produce the first radiographic exposure of his wife’s hand. Over the past 35 years there has been a revolution in body imaging, which has been paralleled by developments in computer technology.
+
+Plain radiography
+X-rays are photons (a type of electromagnetic radiation)
+
+
+
+Tungsten filament
+
+Focusing cup
+
+
+
+Tungsten target
+
+Glass X-ray tube
+
+
+
+and are generated from a complex X-ray tube, which is a
+type of cathode ray tube (Fig. 1.2). The X-rays are then	Cathode
+collimated (i.e., directed through lead-lined shutters to stop them from fanning out) to the appropriate area of the body.
+
+
+X-rays	Anode
+
+As the X-rays pass through the body they are attenuated
+(reduced in energy) by the tissues. Those X-rays that pass	Fig. 1.2  Cathode ray tube for the production of X-rays.
+through the tissues interact with the photographic film. In the body:
+
+■     air attenuates X-rays a little;
+■     fat  attenuates  X-rays  more  than  air  but  less  than water; and
+■     bone attenuates X-rays the most.
+
+
+These differences in attenuation result in differences in the level of exposure of the film. When the photographic film is developed, bone appears white on the film because this region of the film has been exposed to the least amount of  X-rays. Air appears dark on the film because these regions were exposed to the greatest number of X-rays.
+Modifications to this X-ray technique allow a continu-ous stream of X-rays to be produced from the X-ray tube and collected on an input screen to allow real-time visual-ization of moving anatomical structures, barium studies, angiography, and fluoroscopy (Fig. 1.3).
+
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+Fig. 1.3  Fluoroscopy unit.
+
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+5
+The Body
+
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+
+Contrast agents
+To demonstrate specific structures, such as bowel loops or arteries, it may be necessary to fill these structures with a substance that attenuates X-rays more than bowel loops or arteries do normally. It is, however, extremely important that these substances are nontoxic. Barium sulfate, an insoluble salt, is a nontoxic, relatively high-density agent that is extremely useful in the examination of the gastro-intestinal tract. When a barium sulfate suspension is ingested it attenuates X-rays and can therefore be used to demonstrate the bowel lumen (Fig. 1.4). It is common to add air to the barium sulfate suspension, by either ingest-ing “fizzy” granules or directly instilling air into the body cavity, as in a barium enema. This is known as a double-contrast (air/barium) study.
+For some patients it is necessary to inject contrast agents directly into arteries or veins. In this case, iodine-based molecules are suitable contrast agents. Iodine is chosen because it has a relatively high atomic mass and so mark-edly attenuates X-rays, but also, importantly, it is naturally excreted via the urinary system. Intra-arterial and intrave-nous contrast agents are extremely safe and are well toler-ated  by  most  patients.  Rarely,  some  patients  have  an anaphylactic  reaction  to  intra-arterial  or  intravenous
+
+injections, so the necessary precautions must be taken. Intra-arterial and intravenous contrast agents not only help in visualizing the arteries and veins but because they are excreted by the urinary system, can also be used to visualize the kidneys, ureter, and bladder in a process known as intravenous urography.
+
+Subtraction angiography
+During angiography it is often difficult to appreciate the contrast agent in the vessels through the overlying bony structures. To circumvent this, the technique of subtrac-tion  angiography  has  been  developed.  Simply,  one  or two images are obtained before the injection of contrast media. These images are inverted (such that a negative is created from the positive image). After injection of  the contrast media into the vessels, a further series of images are obtained, demonstrating the passage of  the contrast through the arteries into the veins and around the circula-tion. By adding the “negative precontrast image” to the positive postcontrast images, the bones and soft tissues are subtracted to produce a solitary image of  contrast only.  Before  the  advent  of  digital  imaging  this  was  a challenge, but now the use of computers has made this technique  relatively  straightforward  and  instantaneous (Fig. 1.5).
+
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+6	Fig. 1.4  Barium sulfate follow-through.	Fig. 1.5  Digital subtraction angiogram.
+Imaging  •  Diagnostic Imaging Techniques	1
+
+
+
+Ultrasound
+Ultrasonography of the body is widely used for all aspects
+
+
+Doppler ultrasound
+Doppler  ultrasound  enables  determination  of  flow,  its
+
+
+
+of medicine.
+Ultrasound  is  a  very  high  frequency  sound  wave (not electromagnetic radiation) generated by piezoelectric materials, such that a series of sound waves is produced. Importantly, the piezoelectric material can also receive the sound waves that bounce back from the internal organs. The  sound  waves  are  then  interpreted  by  a  powerful computer,  and  a  real-time  image  is  produced  on  the display panel.
+Developments in ultrasound technology, including the size of the probes and the frequency range, mean that a broad range of areas can now be scanned.
+Traditionally  ultrasound  is  used  for  assessing  the abdomen (Fig. 1.6) and the fetus in pregnant women. Ultrasound is also widely used to assess the eyes, neck, soft tissues,  and  peripheral  musculoskeletal  system.  Probes have been placed on endoscopes, and endoluminal ultra-sound of the esophagus, stomach, and duodenum is now routine. Endocavity ultrasound is carried out most com-monly  to  assess  the  genital  tract  in  women  using  a transvaginal  or  transrectal  route.  In  men,  transrectal ultrasound is the imaging method of choice to assess the prostate in those with suspected prostate hypertrophy or malignancy.
+
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+Fig. 1.6  Ultrasound examination of the abdomen.
+
+direction, and its velocity within a vessel using simple ultrasound techniques. Sound waves bounce off moving structures and are returned. The degree of frequency shift determines whether the object is moving away from or toward the probe and the speed at which it is traveling. Precise measurements of blood flow and blood velocity can therefore be obtained, which in turn can indicate sites of blockage in blood vessels.
+
+Computed tomography
+Computed tomography (CT) was invented in the 1970s by Sir Godfrey Hounsfield, who was awarded the Nobel Prize in Medicine in 1979. Since this inspired invention there have been many generations of CT scanners.
+A CT scanner obtains a series of  images of  the body (slices) in the axial plane. The patient lies on a bed, an X-ray tube passes around the body (Fig. 1.7), and a series of images are obtained. A computer carries out a complex mathematical transformation on the multitude of images to produce the final image (Fig. 1.8).
+
+Magnetic resonance imaging
+Nuclear magnetic resonance imaging was first described in 1946 and used to determine the structure of  complex
+
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+Fig. 1.7  Computed tomography scanner.	7
+The Body
+
+
+
+molecules. The process of  magnetic resonance imaging (MRI) is dependent on the free protons in the hydrogen nuclei  in  molecules  of  water  (H2O).  Because  water  is present in almost all biological tissues, the hydrogen proton is ideal. The protons within a patient’s hydrogen nuclei can be regarded as small bar magnets, which are randomly oriented in space. The patient is placed in a strong magnetic field, which aligns the bar magnets. When a pulse of radio waves  is  passed  through  the  patient  the  magnets  are deflected, and as they return to their aligned position they emit small radio pulses. The strength and frequency of the emitted pulses and the time it takes for the protons to return to their pre-excited state produce a signal. These signals are analyzed by a powerful computer, and an image is created (Fig. 1.9).
+By altering the sequence of pulses to which the protons are subjected, different properties of  the protons can be assessed. These properties are referred to as the “weight-ing” of the scan. By altering the pulse sequence and the scanning parameters, T1-weighted images (Fig. 1.10A) and T2-weighted images (Fig. 1.10B) can be obtained. These two types of imaging sequences provide differences in image contrast, which accentuate and optimize different tissue characteristics.
+From the clinical point of view:
+
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+
+Fig. 1.8  Computed tomography scan of the abdomen at vertebral level L2.
+
+
+■     Most T1-weighted images show dark fluid and bright fat—for example, within the brain the cerebrospinal fluid (CSF) is dark.
+■     T2-weighted images demonstrate a bright signal from fluid and an intermediate signal from fat—for example, in the brain the CSF appears white.
+
+
+MRI can also be used to assess flow within vessels and to produce complex angiograms of  the peripheral and cerebral circulation.
+
+Diffusion-weighted imaging
+Diffusion-weighted imaging provides information on the degree of Brownian motion of water molecules in various tissues. There is relatively free diffusion in extracellular
+
+
+
+
+
+
+Fig. 1.9  A T2-weighted MR image in the sagittal plane of the pelvic viscera in a woman.
+
+spaces  and  more  restricted  diffusion  in  intracellular	The  important  difference  between  gamma  rays  and
+
+spaces. In tumors and infarcted tissue, there is an increase in  intracellular  fluid  water  molecules  compared  with the extracellular fluid environment resulting in overall increased restricted diffusion, and therefore identification of abnormal from normal tissue.
+
+
+Nuclear medicine imaging
+
+X-rays is that gamma rays are produced from within the nucleus of  an atom when an unstable nucleus decays, whereas X-rays are produced by bombarding an atom with electrons.
+For an area to be visualized, the patient must receive a gamma ray emitter, which must have a number of proper-ties to be useful, including:
+
+
+
+Nuclear medicine involves imaging using gamma rays, 8	which  are  another  type  of  electromagnetic  radiation.
+
+■     a reasonable half-life (e.g., 6 to 24 hours), ■     an easily measurable gamma ray, and
+Imaging  •  Nuclear Medicine Imaging	1
+
+
+■     energy deposition in as low a dose as possible in the patient’s tissues.
+
+The most commonly used radionuclide (radioisotope) is technetium-99m. This may be injected as a technetium salt  or  combined  with  other  complex  molecules.  For example, by combining technetium-99m with methylene diphosphonate (MDP), a radiopharmaceutical is produced. When  injected  into  the  body  this  radiopharmaceutical specifically  binds  to  bone,  allowing  assessment  of  the skeleton. Similarly, combining technetium-99m with other compounds permits assessment of other parts of the body, for example the urinary tract and cerebral blood flow.
+Depending   on   how   the   radiopharmaceutical   is absorbed, distributed, metabolized, and excreted by the body after injection, images are obtained using a gamma camera (Fig. 1.11).
+
+Positron emission tomography
+Positron   emission   tomography   (PET)   is   an   imaging modality for detecting positron-emitting radionuclides. A
+A	positron is an anti-electron, which is a positively charged particle  of  antimatter.  Positrons  are  emitted  from  the decay of proton-rich radionuclides. Most of these radionu-clides are made in a cyclotron and have extremely short half-lives.
+The most commonly used PET radionuclide is fluorode-oxyglucose  (FDG)  labeled  with  fluorine-18  (a  positron
+
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+B
+
+Fig. 1.10  T1-weighted (A) and T2-weighted (B) MR images of the
+brain in the coronal plane.	Fig. 1.11  A gamma camera.
+
+
+
+
+
+
+9
+The Body
+
+
+
+emitter). Tissues that are actively metabolizing glucose take up this compound, and the resulting localized high concentration of this molecule compared to background emission is detected as a “hot spot.”
+PET has become an important imaging modality in the detection of  cancer and the assessment of  its treatment and recurrence.
+
+Single photon emission computed tomography
+Single photon emission computed tomography (SPECT)
+
+radiograph; that is, with the patient’s back closest to the X-ray tube.).
+Occasionally, when patients are too unwell to stand erect, films are obtained on the bed in an anteroposterior (AP) position. These films are less standardized than PA films, and caution should always be taken when interpret-ing AP radiographs.
+The   plain   chest   radiograph   should   always   be checked for quality. Film markers should be placed on the appropriate side. (Occasionally patients have dextrocardia,
+
+is   an   imaging   modality   for   detecting   gamma   rays	which may be misinterpreted if the film marker is placed
+
+emitted from the decay of injected radionuclides such as technetium-99m, iodine-123, or iodine-131. The rays are detected by a 360-degree rotating camera, which allows the construction of 3D images. SPECT can be used to diagnose a wide range of disease conditions such as coronary artery disease and bone fractures.
+
+IMAGE INTERPRETATION
+
+Imaging is necessary in most clinical specialties to diagnose pathological changes to tissues. It is paramount to appreci-ate what is normal and what is abnormal. An appreciation of how the image is obtained, what the normal variations are, and what technical considerations are necessary to obtain a radiological diagnosis. Without understanding the anatomy of the region imaged, it is impossible to comment on the abnormal.
+
+Plain radiography
+Plain radiographs are undoubtedly the most common form of  image obtained in a hospital or local practice. Before interpretation, it is important to know about the imaging technique and the views obtained as standard.
+In most instances (apart from chest radiography) the X-ray tube is 1 m away from the X-ray film. The object in question, for example a hand or a foot, is placed upon the film. When describing subject placement for radiography, the part closest to the X-ray tube is referred to first and that closest to the film is referred to second. For example, when positioning a patient for an anteroposterior (AP) radio-graph, the more anterior part of the body is closest to the tube and the posterior part is closest to the film.
+When X-rays are viewed on a viewing box, the right side of the patient is placed to the observer’s left; therefore, the observer views the radiograph as though looking at a patient in the anatomical position.
+
+Chest radiograph
+
+inappropriately.)  A  good-quality  chest  radiograph  will demonstrate the lungs, cardiomediastinal contour, dia-phragm, ribs, and peripheral soft tissues.
+
+Abdominal radiograph
+Plain  abdominal  radiographs  are  obtained  in  the  AP supine position. From time to time an erect plain abdominal radiograph is obtained when small bowel obstruction is suspected.
+
+Gastrointestinal contrast examinations
+High-density contrast medium is ingested to opacify the esophagus, stomach, small bowel, and large bowel. As described previously (p. 6), the bowel is insufflated with air (or carbon dioxide) to provide a double-contrast study. In many countries, endoscopy has superseded upper gastro-intestinal imaging, but the mainstay of imaging the large bowel is the double-contrast barium enema. Typically the patient  needs  to  undergo  bowel  preparation,  in  which powerful cathartics are used to empty the bowel. At the time of  the examination a small tube is placed into the rectum and a barium suspension is run into the large bowel. The patient undergoes a series of twists and turns so that the contrast passes through the entire large bowel. The contrast is emptied and air is passed through the same tube to insufflate the large bowel. A thin layer of barium coats the normal mucosa, allowing mucosal detail to be visualized (see Fig. 1.4).
+
+Urological contrast studies
+Intravenous urography is the standard investigation for assessing the urinary tract. Intravenous contrast medium is injected, and images are obtained as the medium is excreted through the kidneys. A series of films are obtained during this period from immediately after the injection up to approximately 20 minutes later, when the bladder is full of contrast medium.
+This series of  radiographs demonstrates the kidneys,
+
+The  chest  radiograph  is  one  of  the  most  commonly	ureters, and bladder and enables assessment of the retro-
+
+requested plain radiographs. An image is taken with the 10	patient  erect  and  placed  posteroanteriorly  (PA  chest
+
+peritoneum and other structures that may press on the urinary tract.
+Imaging  •  Safety in Imaging	1
+
+
+
+
+Computed tomography
+Computed tomography is the preferred terminology rather
+
+and  a  series  of  representative  films  are  obtained  for clinical use.
+
+
+
+than computerized tomography, though both terms are used interchangeably by physicians.
+It is important for the student to understand the presen-tation of  images. Most images are acquired in the axial plane and viewed such that the observer looks from below and upward toward the head (from the foot of the bed). By implication:
+
+
+SAFETY IN IMAGING
+
+Whenever a patient undergoes an X-ray or nuclear medi-cine investigation, a dose of radiation is given (Table 1.1). As a general principle it is expected that the dose given is as low as reasonably possible for a diagnostic image to be obtained. Numerous laws govern the amount of radiation
+
+
+
+
+■     the right side of  the patient is on the left side of  the image, and
+■     the uppermost border of the image is anterior.
+
+Many patients are given oral and intravenous contrast
+
+exposure that a patient can undergo for a variety of proce-dures, and these are monitored to prevent any excess or additional dosage. Whenever a radiograph is booked, the clinician ordering the procedure must appreciate its neces-sity and understand the dose given to the patient to ensure that the benefits significantly outweigh the risks.
+
+
+
+media to differentiate bowel loops from other abdominal organs and to assess the vascularity of normal anatomical structures. When intravenous contrast is given, the earlier the images are obtained, the greater the likelihood of arte-rial enhancement. As the time is delayed between injection and image acquisition, a venous phase and an equilibrium phase are also obtained.
+The great advantage of  CT scanning is the ability to extend and compress the gray scale to visualize the bones, soft tissues, and visceral organs. Altering the window set-tings and window centering provides the physician with specific information about these structures.
+
+Magnetic resonance imaging
+There is no doubt that MRI has revolutionized the under-standing and interpretation of the brain and its coverings. Furthermore, it has significantly altered the practice of musculoskeletal  medicine  and  surgery.  Images  can  be obtained in any plane and in most sequences. Typically the images are viewed using the same principles as CT. Intrave-nous contrast agents are also used to further enhance tissue contrast. Typically, MRI contrast agents contain paramag-netic substances (e.g., gadolinium and manganese).
+
+Imaging modalities such as ultrasound and MRI are ideal because they do not impart significant risk to the patient. Moreover, ultrasound imaging is the modality of choice for assessing the fetus.
+Any  imaging  device  is  expensive,  and  consequently the more complex the imaging technique (e.g., MRI) the more expensive the investigation. Investigations must be carried out judiciously, based on a sound clinical history and examination, for which an understanding of anatomy is vital.
+
+
+
+
+
+
+Table 1.1    The approximate dosage of radiation exposure as an order of magnitude
+
+Typical	Equivalent duration effective	of background
+Examination	dose (mSv)	exposure
+Chest radiograph	0.02	3 days
+Abdomen	1.00	6 months
+Intravenous urography	2.50	14 months
+
+
+
+Nuclear medicine imaging
+Most  nuclear  medicine  images  are  functional  studies. Images are usually interpreted directly from a computer,
+
+
+CT scan of head
+CT scan of abdomen and pelvis
+
+
+2.30	1 year
+10.00	4.5 years
+
+
+
+
+
+
+
+
+
+
+11
+The Body
+
+
+Body systems SKELETAL SYSTEM
+
+The skeleton can be divided into two subgroups, the axial skeleton and the appendicular skeleton. The axial skeleton consists of  the bones of  the skull (cranium), vertebral column,  ribs,  and  sternum,  whereas  the  appendicular skeleton consists of the bones of the upper and lower limbs (Fig. 1.12).
+The skeletal system consists of cartilage and bone.
+
+
+Cartilage
+Cartilage is an avascular form of connective tissue consist-ing of extracellular fibers embedded in a matrix that con-tains cells localized in small cavities. The amount and kind of extracellular fibers in the matrix varies depending on the type of cartilage. In heavy weightbearing areas or areas prone to pulling forces, the amount of collagen is greatly increased and the cartilage is almost inextensible. In con-trast, in areas where weightbearing demands and stress are less, cartilage containing elastic fibers and fewer collagen fibers is common. The functions of cartilage are to:
+
+■     support soft tissues,
+■     provide a smooth, gliding surface for bone articulations at joints, and
+■     enable the development and growth of long bones.
+
+There are three types of cartilage:
+
+
+■     hyaline—most common; matrix contains a moderate amount of  collagen fibers (e.g., articular surfaces of bones);
+■     elastic—matrix contains collagen fibers along with a large number of elastic fibers (e.g., external ear);
+■     fibrocartilage—matrix contains a limited number of cells and ground substance amidst a substantial amount of collagen fibers (e.g., intervertebral discs).
+
+
+
+
+
+
+Axial skeleton
+
+Appendicular skeleton
+
+
+Cartilage is nourished by diffusion and has no blood	Fig. 1.12  The axial skeleton and the appendicular skeleton. vessels, lymphatics, or nerves.
+
+
+
+
+
+
+
+
+
+12
+Body Systems  •  Skeletal System	1
+
+
+Bone
+Bone is a calcified, living, connective tissue that forms the majority of  the skeleton. It consists of  an intercellular calcified matrix, which also contains collagen fibers, and several types of cells within the matrix. Bones function as:
+
+■     supportive structures for the body, ■     protectors of vital organs,
+■     reservoirs of calcium and phosphorus,
+■     levers on which muscles act to produce movement, and ■     containers for blood-producing cells.
+Os trigonum There are two types of bone, compact and spongy (tra-
+becular or cancellous). Compact bone is dense bone that forms the outer shell of all bones and surrounds spongy bone. Spongy bone consists of spicules of bone enclosing cavities containing blood-forming cells (marrow). Classifi-cation of bones is by shape.
+
+
+■     Long bones are tubular (e.g., humerus in upper limb; femur in lower limb).
+■     Short bones are cuboidal (e.g., bones of the wrist and ankle).
+■     Flat bones consist of two compact bone plates separated by spongy bone (e.g., skull).
+■     Irregular bones are bones with various shapes (e.g., bones of the face).
+■     Sesamoid bones are round or oval bones that develop in tendons.
+
+
+
+A
+
+
+Sesamoid bones
+
+
+
+
+In the clinic
+
+Accessory and sesamoid bones
+These are extra bones that are not usually found as part of the normal skeleton, but can exist as a normal variant in many people. They are typically found in multiple locations in the wrist and hands, ankles and feet (Fig. 1.13). These should not be mistaken for fractures on imaging.
+Sesamoid bones are embedded within tendons, the largest of which is the patella. There are many other sesamoids in the body particularly in tendons of the hands and feet, and most frequently in flexor tendons of the thumb and big toe.
+Degenerative and inflammatory changes of, as well as mechanical stresses on, the accessory bones and sesamoids can cause pain, which can be treated with physiotherapy and targeted steroid injections, but in some severe cases it may be necessary to surgically remove the bone.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+B	Os naviculare
+
+Fig. 1.13  Accessory and sesamoid bones. A. Radiograph of the ankle region showing an accessory bone (os trigonum). B. Radiograph of the feet showing numerous sesamoid bones and an accessory bone (os naviculare).
+
+
+
+13
+The Body
+
+
+
+Bones are vascular and are innervated. Generally, an adjacent artery gives off a nutrient artery, usually one per bone, that directly enters the internal cavity of the bone and supplies the marrow, spongy bone, and inner layers of compact bone. In addition, all bones are covered externally, except in the area of a joint where articular cartilage is present, by a fibrous connective tissue membrane called the periosteum, which has the unique capability of forming new bone.This membrane receives blood vessels whose branches supply the outer layers of compact bone. A bone stripped of its periosteum will not survive. Nerves accompany the
+
+vessels that supply the bone and the periosteum. Most of the nerves passing into the internal cavity with the nutrient artery are vasomotor fibers that regulate blood flow. Bone itself has few sensory nerve fibers. On the other hand, the periosteum is supplied with numerous sensory nerve fibers and is very sensitive to any type of injury.
+Developmentally, all bones come from mesenchyme by either intramembranous ossification, in which mesenchy-mal models of bones undergo ossification, or endochondral ossification, in which cartilaginous models of bones form from mesenchyme and undergo ossification.
+
+
+
+
+
+
+In the clinic
+
+Determination of skeletal age
+Throughout life the bones develop in a predictable way to form the skeletally mature adult at the end of puberty. In western countries skeletal maturity tends to occur between the ages of 20 and 25 years. However, this may well vary according to geography and socioeconomic conditions. Skeletal maturity will also be determined by genetic factors and disease states.
+Up until the age of skeletal maturity, bony growth and development follows a typically predictable ordered state, which can be measured through either ultrasound, plain radiographs, or MRI scanning. Typically, the nondominant (left) hand is radiographed, and the radiograph is compared to a series of standard radiographs. From these images the bone age can be determined (Fig. 1.14).
+In certain disease states, such as malnutrition and hypothyroidism, bony maturity may be slow. If the skeletal bone age is significantly reduced from the patient’s true age, treatment may be required.
+In the healthy individual the bone age accurately represents the true age of the patient. This is important in determining the true age of the subject. This may also have medicolegal importance.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A	B
+
+
+
+
+
+
+
+
+
+Cboanrpeasl
+
+
+
+C	D
+
+Fig. 1.14  A developmental series of radiographs showing the progressive ossification of carpal (wrist) bones from 3 (A) to 10 (D) years of age.
+
+
+
+
+
+
+
+14
+Body Systems  •  Skeletal System	1
+
+
+
+In the clinic
+
+Bone marrow transplants
+The bone marrow serves an important function. There are two types of bone marrow, red marrow (otherwise known as myeloid tissue) and yellow marrow. Red blood cells, platelets, and most white blood cells arise from within the red marrow. In the yellow marrow a few white cells are made; however, this marrow is dominated by large fat globules (producing its yellow appearance) (Fig. 1.15).
+From birth most of the body’s marrow is red; however, as the subject ages, more red marrow is converted into yellow marrow within the medulla of the long and
+flat bones.
+Bone marrow contains two types of stem cells. Hemopoietic stem cells give rise to the white blood cells, red blood cells, and platelets. Mesenchymal stem cells differentiate into structures that form bone, cartilage,
+and muscle.
+There are a number of diseases that may involve the bone marrow, including infection and malignancy. In patients who develop a bone marrow malignancy (e.g., leukemia) it may be possible to harvest nonmalignant cells from the patient’s bone marrow or cells from another person’s bone marrow. The patient’s own marrow can be destroyed with chemotherapy or radiation and the new cells infused. This treatment is bone marrow transplantation.
+
+
+
+Red marrow in body of lumbar vertebra
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Yellow marrow in femoral head
+
+Fig. 1.15  T1-weighted image in the coronal plane, demonstrating the relatively high signal intensity returned from the femoral heads and proximal femoral necks, consistent with yellow marrow. In this young patient, the vertebral bodies return an intermediate darker signal that represents red marrow. There is relatively little fat in these vertebrae; hence the lower signal return.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+15
+The Body
+
+
+
+In the clinic
+
+Bone fractures
+Fractures occur in normal bone because of abnormal load or stress, in which the bone gives way (Fig. 1.16A). Fractures may also occur in bone that is of poor quality (osteoporosis); in such cases a normal stress is placed upon a bone that is not of sufficient quality to withstand this force and subsequently fractures.
+In children whose bones are still developing, fractures may occur across the growth plate or across the shaft. These shaft fractures typically involve partial cortical disruption, similar to breaking a branch of a young tree; hence they are termed “greenstick” fractures.
+After a fracture has occurred, the natural response is to heal the fracture. Between the fracture margins a blood clot is formed into which new vessels grow. A jelly-like matrix is formed, and further migration of collagen-producing cells occurs. On this soft tissue framework, calcium hydroxyapatite is produced by osteoblasts and forms insoluble crystals, and then bone matrix is laid down. As more bone is produced, a callus can be demonstrated forming across the fracture site.
+Treatment of fractures requires a fracture line reduction. If this cannot be maintained in a plaster of Paris cast, it may require internal or external fixation with screws and metal rods (Fig. 1.16B).
+
+
+
+
+
+
+In the clinic
+
+Avascular necrosis
+Avascular necrosis is cellular death of bone resulting from a temporary or permanent loss of blood supply to that bone. Avascular necrosis may occur in a variety of medical conditions, some of which have an etiology that is less than clear. A typical site for avascular necrosis is a fracture across the femoral neck in an elderly patient. In these patients there is loss of continuity of the cortical medullary blood flow with loss of blood flow deep to the retinacular fibers. This essentially renders the femoral head bloodless; it subsequently undergoes necrosis and collapses (Fig. 1.17). In these patients it is necessary to replace the femoral head with a prosthesis.
+
+
+
+
+
+
+
+
+
+
+
+
+
+A
+
+
+
+
+
+
+
+
+
+B
+
+Fig. 1.16  Radiograph, lateral view, showing fracture of the ulna at the elbow joint (A) and repair of this fracture (B) using internal fixation with a plate and multiple screws.
+
+
+
+
+
+
+
+
+Wasting of gluteal muscle
+
+
+
+Avascular necrosis	Bladder	Normal left hip
+
+Fig. 1.17  Image of the hip joints demonstrating loss of height of the right femoral head with juxta-articular bony sclerosis and subchondral cyst formation secondary to avascular necrosis. There is also significant wasting of the muscles supporting the hip, which is secondary to disuse and pain.
+16
+Body Systems  •  Skeletal System	1
+
+
+
+In the clinic
+
+Epiphyseal fractures
+As the skeleton develops, there are stages of intense growth typically around the ages of 7 to 10 years and later in puberty. These growth spurts are associated with increased cellular activity around the growth plate between the head and shaft of a bone. This increase in activity renders the growth plates more vulnerable to injuries, which may occur from dislocation across a growth plate or fracture through a growth plate. Occasionally an injury may result in growth plate compression, destroying that region of the growth plate, which may result in asymmetrical growth across that joint region. All fractures across the growth plate must be treated with care and expediency, requiring fracture reduction.
+
+
+
+
+
+
+
+
+
+
+Bone	Articular cavity	Bone
+
+A Synovial joint
+
+
+
+Bone	Connective tissue	Bone
+
+B Solid joint
+
+Joints	Fig. 1.18  Joints. A. Synovial joint. B. Solid joint.
+The  sites  where  two  skeletal  elements  come  together
+
+are termed joints. The two general categories of  joints (Fig. 1.18) are those in which:
+
+
+■     The synovial membrane attaches to the margins of the joint surfaces at the interface between the cartilage and
+
+
+■     the skeletal elements are separated by a cavity (i.e., synovial joints), and
+■     there is no cavity and the components are held together by connective tissue (i.e., solid joints).
+
+bone and encloses the articular cavity. The synovial membrane is highly vascular and produces synovial fluid, which percolates into the articular cavity and lubricates  the  articulating  surfaces.  Closed  sacs  of synovial membrane also occur outside joints, where
+
+
+
+
+Blood vessels that cross over a joint and nerves that innervate muscles acting on a joint usually contribute articular branches to that joint.
+
+Synovial joints
+Synovial joints are connections between skeletal compo-nents where the elements involved are separated by a narrow articular cavity (Fig. 1.19). In addition to contain-ing an articular cavity, these joints have a number of characteristic features.
+First, a layer of  cartilage, usually hyaline cartilage, covers the articulating surfaces of the skeletal elements. In other words, bony surfaces do not normally contact one
+
+they form synovial bursae or tendon sheaths. Bursae often intervene between structures, such as tendons and bone, tendons and joints, or skin and bone, and reduce the friction of  one structure moving over the other.  Tendon  sheaths  surround  tendons  and  also reduce friction.
+■     The fibrous membrane is formed by dense connective tissue and surrounds and stabilizes the joint. Parts of the fibrous membrane may thicken to form ligaments, which further stabilize the joint. Ligaments outside the capsule usually provide additional reinforcement.
+
+
+Another common but not universal feature of synovial
+
+
+
+another directly. As a consequence, when these joints are viewed in normal radiographs, a wide gap seems to sepa-rate the adjacent bones because the cartilage that covers the articulating surfaces is more transparent to X-rays than bone.
+A second characteristic feature of synovial joints is the presence of a joint capsule consisting of an inner syno-vial membrane and an outer fibrous membrane.
+
+joints is the presence of additional structures within the area enclosed by the capsule or synovial membrane, such as articular discs (usually composed of  fibrocartilage), fat pads, and tendons. Articular discs absorb compres-sion forces, adjust to changes in the contours of joint sur-faces  during  movements,  and  increase  the  range  of movements that can occur at joints. Fat pads usually occur
+between the synovial membrane and the capsule and move	17
+The Body
+
+
+Tendon Sheath
+
+
+
+Joint capsule
+
+Fibrous membrane
+
+Synovial membrane
+
+
+Hyaline cartilage
+Fat pad
+
+Articular cavity
+
+Articular disc
+
+
+
+Bone
+Bone
+Hyaline cartilage
+Bone
+
+
+Articular cavity
+
+
+
+
+A
+
+Bone
+
+
+
+
+B	Skin	Bursa
+
+
+
+Fibrous membrane
+Synovial membrane
+
+
+Fig. 1.19  Synovial joints. A. Major features of a synovial joint. B. Accessory structures associated with synovial joints.
+
+
+
+
+
+
+into and out of regions as joint contours change during movement. Redundant regions of the synovial membrane and fibrous membrane allow for large movements at joints.
+
+Descriptions of synovial joints based on shape and movement
+
+bicondylar (two sets of contact points), condylar (ellip-soid), saddle, and ball and socket;
+■     based on movement, synovial joints are described as uniaxial (movement in one plane), biaxial (movement in  two  planes),  and  multiaxial  (movement  in  three planes).
+
+Synovial   joints   are   described   based   on   shape   and
+movement:	Hinge joints are uniaxial, whereas ball and socket joints
+are multiaxial. ■     based on the shape of their articular surfaces, synovial
+joints  are  described  as  plane  (flat),  hinge,  pivot,
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+18
+Body Systems  •  Skeletal System	1
+
+
+
+
+Specific types of synovial joints (Fig. 1.20)
+
+adduction,   circumduction,   and   rotation   (e.g.,   hip joint)
+
+
+
+■     Plane joints—allow sliding or gliding movements when one bone moves across the surface of  another (e.g., acromioclavicular joint)
+■     Hinge joints—allow movement around one axis that passes transversely through the joint; permit flexion and extension (e.g., elbow [humero-ulnar] joint)
+■     Pivot joints—allow movement around one axis that passes longitudinally along the shaft of the bone; permit rotation (e.g., atlanto-axial joint)
+
+Solid joints
+Solid  joints  are  connections  between  skeletal  elements where  the  adjacent  surfaces  are  linked  together  either by fibrous connective tissue or by cartilage, usually fibro-cartilage (Fig. 1.21). Movements at these joints are more restricted than at synovial joints.
+Fibrous   joints   include   sutures,   gomphoses,   and syndesmoses.
+
+■     Bicondylar joints—allow movement mostly in one axis with limited rotation around a second axis; formed by two convex condyles that articulate with concave or flat surfaces (e.g., knee joint)
+■     Condylar  (ellipsoid)  joints—allow  movement  around two axes that are at right angles to each other; permit flexion, extension, abduction, adduction, and circum-duction (limited) (e.g., wrist joint)
+■     Saddle joints—allow movement around two axes that are at right angles to each other; the articular surfaces
+
+■     Sutures occur only in the skull where adjacent bones are linked by a thin layer of connective tissue termed a sutural ligament.
+■     Gomphoses occur only between the teeth and adjacent bone. In these joints, short collagen tissue fibers in the periodontal ligament run between the root of the tooth and the bony socket.
+■     Syndesmoses are joints in which two adjacent bones are linked by a ligament. Examples are the ligamentum flavum,  which  connects  adjacent  vertebral  laminae,
+
+are saddle shaped; permit flexion, extension, abduction,	and  an  interosseous  membrane,  which  links,  for adduction, and circumduction (e.g., carpometacarpal	example, the radius and ulna in the forearm.
+joint of the thumb)
+■     Ball   and   socket   joints—allow   movement   around	Cartilaginous   joints   include   synchondroses   and multiple  axes;  permit  flexion,  extension,  abduction,       symphyses.
+
+B	Humerus
+
+Ulna	Radius
+Synovial membrane
+
+
+
+Articular disc
+
+
+
+A	Synovial cavity
+
+
+Cartilage
+
+Wrist joint
+
+
+
+Olecranon
+C	Ulna
+
+
+
+Radius
+
+
+
+Odontoid process of axis
+
+
+Trapezium Synovial membrane
+
+
+
+
+
+Metacarpal I
+
+Femur
+
+D	E
+
+Atlas
+Synovial membrane
+
+F
+
+
+
+Fig. 1.20  Various types of synovial joints. A. Condylar (wrist). B. Gliding (radio-ulnar). C. Hinge (elbow). D. Ball and socket (hip). E. Saddle (carpometacarpal of thumb). F. Pivot (atlanto-axial).
+
+19
+The Body
+
+
+
+SOLID JOINTS
+
+
+Fibrous	Cartilaginous
+
+
+Sutures
+
+Sutural ligament
+
+
+
+Skull	Synchondrosis
+
+Head
+
+
+Gomphosis
+
+
+Tooth
+
+
+Cartilage of growth plate
+
+Long bone
+
+
+
+Shaft Periodontal
+ligament
+
+Bone
+
+Symphysis
+
+
+Syndesmosis
+
+Intervertebral discs
+
+
+
+
+
+Radius	Ulna
+
+
+Interosseous membrane
+Pubic symphysis
+
+
+
+
+
+
+
+Fig. 1.21  Solid joints.
+
+
+■     Synchondroses occur where two ossification centers in a developing bone remain separated by a layer of cartilage, for example, the growth plate that occurs between the head and shaft of developing long bones. These joints allow bone growth and eventually become
+20	completely ossified.
+
+■     Symphyses occur where two separate bones are inter-connected by cartilage. Most of  these types of  joints occur in the midline and include the pubic symphysis between the two pelvic bones, and intervertebral discs between adjacent vertebrae.
+Body Systems  •  Skeletal System	1
+
+
+
+In the clinic
+
+Degenerative joint disease
+Degenerative joint disease is commonly known as osteoarthritis or osteoarthrosis. The disorder is related to aging but not caused by aging. Typically there are decreases in water and proteoglycan content within the cartilage. The cartilage becomes more fragile and more susceptible to mechanical disruption (Fig. 1.22). As the cartilage wears, the underlying bone becomes fissured and also thickens. Synovial fluid may be forced into small cracks that appear in the bone’s surface, which produces large cysts. Furthermore, reactive juxta-articular bony nodules are formed (osteophytes) (Fig. 1.23). As these processes occur, there is slight deformation, which alters the biomechanical forces through the joint. This in turn creates abnormal stresses, which further disrupt the joint.
+
+
+
+In the United States, osteoarthritis accounts for up to
+one-quarter of primary health care visits and is regarded as a significant problem.
+The etiology of osteoarthritis is not clear; however, osteoarthritis can occur secondary to other joint diseases, such as rheumatoid arthritis and infection. Overuse of joints and abnormal strains, such as those experienced by people who play sports, often cause one to be more susceptible to chronic joint osteoarthritis.
+Various treatments are available, including weight reduction, proper exercise, anti-inflammatory drug treatment, and joint replacement (Fig. 1.24).
+
+
+Osteophytes
+
+
+
+
+
+
+
+Cartilage loss
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Femoral condyles
+
+Patella
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Cartilage loss	Loss of joint space
+
+
+
+Fig. 1.22  This operative photograph demonstrates the focal areas of cartilage loss in the patella and femoral condyles throughout the knee joint.
+
+Fig. 1.23  This radiograph demonstrates the loss of joint space in the medial compartment and presence of small spiky osteophytic regions at the medial lateral aspect of the joint.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+21
+The Body
+
+
+In the clinic—cont’d
+
+Arthroscopy
+Arthroscopy is a technique of visualizing the inside of a joint using a small telescope placed through a tiny incision in the skin. Arthroscopy can be performed in most joints. However, it is most commonly performed in the knee, shoulder, ankle, and hip joints.
+Arthroscopy allows the surgeon to view the inside of the joint and its contents. Notably, in the knee, the menisci and the ligaments are easily seen, and it is possible using separate puncture sites and specific instruments to remove the menisci and replace the cruciate ligaments. The advantages of arthroscopy are that it is performed through small incisions, it enables patients to quickly recover and return to normal activity, and it only requires either a light anesthetic or regional anesthesia during the procedure.
+
+
+
+
+Fig. 1.24  After knee replacement. This radiograph shows the position of the prosthesis.
+
+
+
+
+
+In the clinic
+
+Joint replacement
+Joint replacement is undertaken for a variety of reasons. These predominantly include degenerative joint disease and joint destruction. Joints that have severely degenerated or lack their normal function are painful. In some patients, the pain may be so severe that it prevents them from leaving the house and undertaking even the smallest of activities without discomfort.
+Large joints are commonly affected, including the hip, knee, and shoulder. However, with ongoing developments in joint replacement materials and surgical techniques, even small joints of the fingers can be replaced.
+Typically, both sides of the joint are replaced; in the hip joint the acetabulum will be reamed, and a plastic or metal cup will be introduced. The femoral component will be fitted precisely to the femur and cemented in place (Fig. 1.25).
+Most patients derive significant benefit from joint replacement and continue to lead an active life afterward. In a minority of patients who have been fitted with a metal acetabular cup and metal femoral component, an aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) may develop, possibly caused by a hypersensitivity response to the release of metal ions in adjacent tissues. These patients often have chronic pain and might need additional surgery to replace these joint replacements with safer models.
+
+22
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Artificial femoral head	Acetabulum
+
+Fig. 1.25  This is a radiograph, anteroposterior view, of the pelvis after a right total hip replacement. There are additional significant degenerative changes in the left hip joint, which will also need to be replaced.
+Body Systems  •  Muscular System	1
+
+
+
+SKIN AND FASCIAS Skin
+The skin is the largest organ of the body. It consists of the epidermis and the dermis. The epidermis is the outer cel-lular layer of  stratified squamous epithelium, which is avascular and varies in thickness. The dermis is a dense bed of vascular connective tissue.
+The skin functions as a mechanical and permeability barrier, and as a sensory and thermoregulatory organ. It also can initiate primary immune responses.
+
+
+Fascia
+Fascia is connective tissue containing varying amounts of fat that separate, support, and interconnect organs and structures, enable movement of one structure relative to another, and allow the transit of vessels and nerves from one area to another. There are two general categories of fascia: superficial and deep.
+
+
+In the clinic
+
+The importance of fascias
+A fascia is a thin band of tissue that surrounds muscles, bones, organs, nerves, and blood vessels and often remains uninterrupted as a 3D structure between tissues. It provides important support for tissues and can provide a boundary between structures.
+Clinically, fascias are extremely important because they often limit the spread of infection and malignant disease. When infections or malignant diseases cross a fascial plain, a primary surgical clearance may require a far more extensive dissection to render the area free of tumor or infection.
+A typical example of the clinical importance of a fascial layer would be of that covering the psoas muscle. Infection within an intervertebral body secondary to tuberculosis can pass laterally into the psoas muscle. Pus fills the psoas muscle but is limited from further spread by the psoas fascia, which surrounds the muscle and extends inferiorly into the groin pointing below the inguinal ligament.
+
+
+
+■     Superficial (subcutaneous) fascia lies just deep to and is attached to the dermis of the skin. It is made up of loose connective tissue usually containing a large amount of fat. The thickness of the superficial fascia (subcutane-ous tissue) varies considerably, both from one area of the body to another and from one individual to another. The superficial fascia allows movement of the skin over deeper areas of the body, acts as a conduit for vessels and nerves coursing to and from the skin, and serves as an energy (fat) reservoir.
+■     Deep fascia usually consists of dense, organized connec-tive tissue. The outer layer of deep fascia is attached to the deep surface of  the superficial fascia and forms a thin fibrous covering over most of the deeper region of the body. Inward extensions of  this fascial layer form intermuscular septa that compartmentalize groups of muscles with similar functions and innervations. Other extensions surround individual muscles and groups of vessels and nerves, forming an investing fascia. Near some joints the deep fascia thickens, forming retinacula. These  fascial  retinacula  hold  tendons  in  place  and prevent them from bowing during movements at the joints. Finally, there is a layer of deep fascia separating the membrane lining the abdominal cavity (the parietal peritoneum) from the fascia covering the deep surface of the muscles of the abdominal wall (the transversalis fascia). This layer is referred to as extraperitoneal
+
+
+In the clinic
+
+Placement of skin incisions and scarring
+Surgical skin incisions are ideally placed along or parallel to Langer’s lines, which are lines of skin tension that correspond to the orientation of the dermal collagen fibers. They tend to run in the same direction as the underlying muscle fibers and incisions that are made along these lines tend to heal better with less scarring. In contrast, incisions made perpendicular to Langer’s lines are more likely to heal with a prominent scar and in some severe cases can lead to raised, firm, hypertrophic, or keloid, scars.
+
+MUSCULAR SYSTEM
+
+The muscular system is generally regarded as consisting of one type of  muscle found in the body—skeletal muscle. However, there are two other types of muscle tissue found in the body, smooth muscle and cardiac muscle, that are important components of other systems. These three types of muscle can be characterized by whether they are con-trolled voluntarily or involuntarily, whether they appear striated (striped) or smooth, and whether they are associ-ated with the body wall (somatic) or with organs and blood vessels (visceral).
+
+
+
+fascia. A similar layer of fascia in the thorax is termed the endothoracic fascia.
+
+■     Skeletal muscle forms the majority of the muscle tissue in  the  body.  It  consists  of  parallel  bundles  of  long,
+
+
+23
+The Body
+
+
+
+multinucleated fibers with transverse stripes, is capable of powerful contractions, and is innervated by somatic and branchial motor nerves. This muscle is used to move bones and other structures, and provides support and gives form to the body. Individual skeletal muscles are often named on the basis of shape (e.g., rhomboid major muscle), attachments (e.g., sternohyoid muscle), function (e.g., flexor pollicis longus muscle), position (e.g., palmar interosseous muscle), or fiber orientation (e.g., external oblique muscle).
+■     Cardiac muscle is striated muscle found only in the walls of  the heart (myocardium) and in some of  the large vessels close to where they join the heart. It consists of a branching network of individual cells linked electri-cally and mechanically to work as a unit. Its contrac-tions are less powerful than those of skeletal muscle and it is resistant to fatigue. Cardiac muscle is innervated by visceral motor nerves.
+■     Smooth muscle (absence of stripes) consists of elongated or spindle-shaped fibers capable of slow and sustained contractions. It is found in the walls of  blood vessels (tunica media), associated with hair follicles in the skin, located in the eyeball, and found in the walls of various structures associated with the gastrointestinal, respira-tory,  genitourinary,  and  urogenital  systems.  Smooth muscle is innervated by visceral motor nerves.
+
+
+In the clinic
+
+Muscle paralysis
+Muscle paralysis is the inability to move a specific muscle or muscle group and may be associated with other neurological abnormalities, including loss of sensation. Major causes include stroke, trauma, poliomyelitis, and iatrogenic factors. Paralysis may be due to abnormalities in the brain, the spinal cord, and the nerves supplying the muscles.
+In the long term, muscle paralysis will produce secondary muscle wasting and overall atrophy of the region due to disuse.
+
+
+
+
+
+In the clinic
+
+Muscle atrophy
+Muscle atrophy is a wasting disorder of muscle. It can be produced by a variety of causes, which include nerve damage to the muscle and disuse.
+Muscle atrophy is an important problem in patients who have undergone long-term rest or disuse, requiring extensive rehabilitation and muscle building exercises to maintain normal activities of daily living.
+
+
+
+
+
+In the clinic
+
+Muscle injuries and strains
+Muscle injuries and strains tend to occur in specific muscle groups and usually are related to a sudden exertion and muscle disruption. They typically occur in athletes.
+Muscle tears may involve a small interstitial injury up to a complete muscle disruption (Fig. 1.26). It is important to
+
+
+
+identify which muscle groups are affected and the extent of the tear to facilitate treatment and obtain a prognosis, which will determine the length of rehabilitation necessary to return to normal activity.
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 1.26  Axial inversion recovery MR imaging series, which suppresses fat and soft tissue and leaves high signal intensity where fluid is seen. A muscle tear in the right adductor longus with
+edema in and around the muscle is shown.	Torn right adductor longus	Normal left adductor longus 24
+Body Systems  •  Cardiovascular System	1
+
+
+
+CARDIOVASCULAR SYSTEM
+
+The cardiovascular system consists of  the heart, which pumps blood throughout the body, and the blood vessels, which are a closed network of  tubes that transport the blood. There are three types of blood vessels:
+
+Examples of large veins are the superior vena cava, the inferior vena cava, and the portal vein.
+■     Small and medium veins contain small amounts of smooth muscle, and the thickest layer is the tunica externa.  Examples  of  small  and  medium  veins  are superficial  veins  in  the  upper  and  lower  limbs  and
+
+
+■     arteries, which transport blood away from the heart; ■     veins, which transport blood toward the heart;
+■     capillaries, which connect the arteries and veins, are the
+
+deeper veins of the leg and forearm.
+■     Venules   are   the   smallest   veins   and   drain   the capillaries.
+
+
+
+smallest of  the blood vessels and are where oxygen, nutrients, and wastes are exchanged within the tissues.
+
+
+Although veins are similar in general structure to arter-ies, they have a number of distinguishing features.
+
+
+
+The walls of  the blood vessels of  the cardiovascular system usually consist of three layers or tunics:
+
+■     The walls of  veins, specifically the tunica media, are thin.
+■     The luminal diameters of veins are large.
+
+
+
+■     tunica externa (adventitia)—the outer connective tissue layer,
+■     tunica media—the middle smooth muscle layer (may also contain varying amounts of elastic fibers in medium and large arteries), and
+■     tunica intima—the inner endothelial lining of the blood vessels.
+
+■     There often are multiple veins (venae comitantes) closely associated with arteries in peripheral regions.
+■     Valves often are present in veins, particularly in periph-eral vessels inferior to the level of the heart. These are usually paired cusps that facilitate blood flow toward the heart.
+
+More  specific  information  about  the  cardiovascular
+
+
+
+Arteries  are  usually  further  subdivided  into  three classes,  according  to  the  variable  amounts  of  smooth muscle and elastic fibers contributing to the thickness of the tunica media, the overall size of  the vessel, and its function.
+
+system  and  how  it  relates  to  the  circulation  of  blood throughout the body will be discussed, where appropriate, in each of the succeeding chapters of the text.
+
+
+
+■     Large elastic arteries contain substantial amounts of elastic fibers in the tunica media, allowing expansion and recoil during the normal cardiac cycle. This helps maintain  a  constant  flow  of  blood  during  diastole. Examples of  large elastic arteries are the aorta, the brachiocephalic trunk, the left common carotid artery, the left subclavian artery, and the pulmonary trunk.
+■     Medium muscular arteries are composed of  a tunica media that contains mostly smooth muscle fibers. This characteristic  allows  these  vessels  to  regulate  their diameter and control the flow of blood to different parts of the body. Examples of medium muscular arteries are most of the named arteries, including the femoral, axil-lary, and radial arteries.
+■     Small arteries and arterioles control the filling of  the capillaries and directly contribute to the arterial pres-sure in the vascular system.
+
+Veins also are subdivided into three classes.
+
+■     Large veins contain some smooth muscle in the tunica media,  but  the  thickest  layer  is  the  tunica  externa.
+
+
+
+In the clinic
+
+Atherosclerosis
+Atherosclerosis is a disease that affects arteries. There is a chronic inflammatory reaction in the walls of the arteries, with deposition of cholesterol and fatty proteins. This may in turn lead to secondary calcification, with reduction in the diameter of the vessels impeding distal flow. The plaque itself may be a site for attraction of platelets that may “fall off” (embolize) distally. Plaque fissuring may occur, which allows fresh clots to form and occlude the vessel.
+The importance of atherosclerosis and its effects depend upon which vessel is affected. If atherosclerosis occurs in the carotid artery, small emboli may form and produce a stroke. In the heart, plaque fissuring may produce an acute vessel thrombosis, producing a myocardial infarction (heart attack). In the legs, chronic narrowing of vessels may limit the ability of the patient to walk and ultimately cause distal ischemia and gangrene of
+the toes.	25
+The Body
+
+
+In the clinic
+
+Varicose veins	Varicose veins Varicose veins are tortuous dilated veins that typically occur
+in the legs, although they may occur in the superficial veins of the arm and in other organs.
+In normal individuals the movement of adjacent leg muscles pumps the blood in the veins to the heart. Blood is also pumped from the superficial veins through the investing layer of fascia of the leg into the deep veins. Valves in these perforating veins may become damaged, allowing blood to pass in the opposite direction. This increased volume and pressure produces dilatation and tortuosity of the superficial veins (Fig. 1.27). Apart from the unsightliness of larger veins, the skin may become pigmented and atrophic with a poor response to tissue trauma. In some patients even small trauma may produce skin ulceration, which requires elevation of the limb and application of pressure bandages to heal.
+Treatment of varicose veins depends on their location, size, and severity. Typically the superficial varicose veins can be excised and stripped, allowing blood only to drain into the deep system.
+
+
+
+
+
+
+
+Fig. 1.27  Photograph demonstrating varicose veins.
+
+
+
+
+
+In the clinic
+
+Anastomoses and collateral circulation
+All organs require a blood supply from the arteries and drainage by veins. Within most organs there are multiple ways of perfusing the tissue such that if the main vessel feeding the organ or vein draining the organ is blocked, a series of smaller vessels (collateral vessels) continue to supply and drain the organ.
+In certain circumstances, organs have more than one vessel perfusing them, such as the hand, which is supplied by the radial and ulnar arteries. Loss of either the radial or the ulnar artery may not produce any symptoms of reduced perfusion to the hand.
+There are circumstances in which loss of a vein produces significant venous collateralization. Some of these venous collaterals become susceptible to bleeding. This is a
+
+
+
+considerable problem in patients who have undergone portal vein thrombosis or occlusion, where venous drainage from the gut bypasses the liver through collateral veins to return to the systemic circulation.
+Normal vascular anastomoses associated with an organ are important. Some organs, such as the duodenum, have a dual blood supply arising from the branches of the celiac trunk and also from the branches of the superior mesenteric artery. Should either of these vessels be damaged, blood supply will be maintained to the organ. The brain has multiple vessels supplying it, dominated by the carotid arteries and the vertebral arteries. Vessels within the brain are end arteries and have a poor collateral circulation; hence any occlusion will produce long-term cerebral damage.
+
+
+
+
+26
+Body Systems  •  Lymphatic System	1
+
+
+
+LYMPHATIC SYSTEM Lymphatic vessels
+Lymphatic vessels form an extensive and complex inter-connected network of channels, which begin as “porous” blind-ended lymphatic capillaries in tissues of  the body and converge to form a number of larger vessels, which ultimately connect with large veins in the root of the neck. Lymphatic vessels mainly collect fluid lost from vascular capillary beds during nutrient exchange processes and deliver it back to the venous side of the vascular system (Fig. 1.28). Also included in this interstitial fluid that drains into the lymphatic capillaries are pathogens, cells of the lymphocytic system, cell products (such as hormones), and
+cell debris.
+In the small intestine, certain fats absorbed and pro-cessed  by  the  intestinal  epithelium  are  packaged  into protein-coated lipid droplets (chylomicrons), which are released from the epithelial cells and enter the interstitial compartment. Together  with  other  components  of  the
+
+interstitial fluid, the chylomicrons drain into lymphatic capillaries (known as lacteals in the small intestine) and are ultimately delivered to the venous system in the neck. The lymphatic system is therefore also a major route of transport for fat absorbed by the gut.
+The fluid in most lymphatic vessels is clear and colorless and is known as lymph. That carried by lymphatic vessels from the small intestine is opaque and milky because of the presence of chylomicrons and is termed chyle.
+There are lymphatic vessels in most areas of the body, including those associated with the central nervous system (Louveau A et al., Nature 2015; 523:337-41; Aspelund A et al., J Exp Med 2015; 212:991-9). Exceptions include bone marrow and avascular tissues such as epithelia and cartilage.
+The movement of lymph through the lymphatic vessels is generated mainly by the indirect action of  adjacent structures, particularly by contraction of skeletal muscles and pulses in arteries. Unidirectional flow is maintained by the presence of valves in the vessels.
+
+
+
+
+
+
+
+Lymphoid tissue
+(containing lymphocytes	Blood vessels and macrophages)
+
+Heart
+
+Capsule
+
+
+Capillary bed
+
+
+
+Lymph node
+
+
+
+
+
+
+
+Lymph vessel carrying lymph
+
+Interstitial fluid
+Cell products and debris
+
+Cells	Pathogens
+
+
+
+
+
+Lymphatic capillaries
+
+Fig. 1.28  Lymphatic vessels mainly collect fluid lost from vascular capillary beds during nutrient exchange processes and deliver it back to the
+venous side of the vascular system.	27
+The Body
+
+
+
+
+Lymph nodes
+Lymph nodes are small (0.1–2.5 cm long) encapsulated structures that interrupt the course of lymphatic vessels and contain elements of the body’s defense system, such as clusters of lymphocytes and macrophages. They act as elaborate  filters  that  trap  and  phagocytose  particulate matter in the lymph that percolates through them. In addi-tion, they detect and defend against foreign antigens that are also carried in the lymph (Fig. 1.28).
+Because  lymph  nodes  are  efficient  filters  and  flow through   them   is   slow,   cells   that   metastasize   from (migrate away from) primary tumors and enter lymphatic vessels  often  lodge  and  grow  as  secondary  tumors  in lymph nodes. Lymph nodes that drain regions that are infected or contain other forms of  disease can enlarge or undergo certain physical changes, such as becoming
+
+
+Cervical nodes (along course of internal jugular vein)
+
+Axillary nodes (in axilla)
+
+Deep nodes (related to aorta and celiac trunk and superior and inferior mesenteric arteries)
+
+
+Pericranial ring (base of head)
+
+
+Tracheal nodes (nodes related to trachea and bronchi)
+
+
+Inguinal nodes (along course of inguinal ligament)
+
+
+
+
+Femoral nodes (along femoral vein)
+
+
+
+“hard” or “tender.” These changes can be used by clini-cians to detect pathologic changes or to track spread of disease.
+A number of regions in the body are associated with clusters or a particular abundance of lymph nodes (Fig. 1.29). Not surprisingly, nodes in many of  these regions drain the body’s surface, the digestive system, or the respi-ratory system. All three of these areas are high-risk sites for the entry of foreign pathogens.
+Lymph nodes are abundant and accessible to palpation
+
+
+Fig. 1.29  Regions associated with clusters or a particular abundance of lymph nodes.
+
+
+
+in the axilla, the groin and femoral region, and the neck. Deep sites that are not palpable include those associated with the trachea and bronchi in the thorax, and with the aorta and its branches in the abdomen.
+
+
+Lymphatic trunks and ducts
+All  lymphatic  vessels  coalesce  to  form  larger  trunks or ducts, which drain into the venous system at sites in the  neck  where  the  internal  jugular  veins  join  the
+
+
+Right jugular trunk
+Right subclavian trunk
+
+Right broncho-mediastinal trunk
+
+
+Left jugular trunk
+Left subclavian trunk
+
+Left broncho-mediastinal trunk
+
+
+Thoracic duct
+
+subclavian   veins   to   form   the   brachiocephalic   veins (Fig. 1.30):
+
+■     Lymph from the right side of the head and neck, the right upper limb, and the right side of  the thorax is carried by lymphatic vessels that connect with veins on the right side of the neck.
+■     Lymph from all other regions of the body is carried by lymphatic vessels that drain into veins on the left side of the neck.
+
+Specific  information  about  the  organization  of  the
+
+lymphatic system in each region of the body is discussed in the appropriate chapter.
+28
+
+Fig. 1.30  Major lymphatic vessels that drain into large veins in the neck.
+Body Systems  •  Nervous System	1
+
+
+
+In the clinic
+
+Lymph nodes
+Lymph nodes are efficient filters and have an internal honeycomb of reticular connective tissue filled with lymphocytes. These lymphocytes act on bacteria, viruses, and other bodily cells to destroy them. Lymph nodes tend to drain specific areas, and if infection occurs within a drainage area, the lymph node will become active. The rapid cell turnover and production of local inflammatory mediators may cause the node to enlarge and become tender.
+
+
+
+Similarly, in patients with malignancy the lymphatics may drain metastasizing cells to the lymph nodes. These can become enlarged and inflamed and will need to be removed if clinically symptomatic.
+Lymph nodes may become diffusely enlarged in certain systemic illnesses (e.g., viral infection), or local groups may become enlarged with primary lymph node malignancies, such as lymphoma (Fig. 1.31).
+
+
+
+
+Left carotid artery
+Thyroid gland	Left jugular vein
+
+Anterior mediastinal mass Superior vena cava	(lymphoma)
+
+
+
+
+
+
+
+
+
+
+
+A
+
+Lymph nodes
+
+B
+
+Ascending aorta	Thoracic aorta
+
+Fig. 1.31  A. This computed tomogram with contrast, in the axial plane, demonstrates the normal common carotid arteries and internal jugular veins with numerous other nonenhancing nodules that represent lymph nodes in a patient with lymphoma. B. This computed tomogram with contrast, in the axial plane, demonstrates a large anterior soft tissue mediastinal mass that represents a lymphoma.
+
+
+
+
+
+NERVOUS SYSTEM
+
+The nervous system can be separated into parts based on structure and on function:
+
+system develop from neural crest cells and as outgrowths of  the CNS. The PNS consists of  the spinal and cranial nerves,  visceral  nerves  and  plexuses,  and  the  enteric system. The detailed anatomy of a typical spinal nerve is
+
+
+
+
+■     structurally, it can be divided into the central nervous system (CNS) and the peripheral nervous system (PNS) (Fig. 1.32);
+■     functionally, it can be divided into somatic and visceral parts.
+
+described in Chapter 2, as is the way spinal nerves are numbered.  Cranial  nerves  are  described  in  Chapter  8. The details of  nerve plexuses are described in chapters dealing with the specific regions in which the plexuses are located.
+
+
+
+The CNS is composed of the brain and spinal cord, both of which develop from the neural tube in the embryo.
+The PNS is composed of all nervous structures outside the CNS that connect the CNS to the body. Elements of this
+
+Central nervous system Brain
+The parts of the brain are the cerebral hemispheres, the cerebellum, and the brainstem. The cerebral hemispheres
+29
+The Body
+
+
+
+
+Peripheral nervous system (PNS)
+
+
+Cranial nerve
+
+
+
+
+
+
+Spinal nerve
+
+
+Central nervous system (CNS)
+
+Brain
+
+
+
+
+
+
+
+Spinal cord
+
+Spinal cord
+The spinal cord is the part of the CNS in the superior two thirds of  the vertebral canal. It is roughly cylindrical in shape, and is circular to oval in cross section with a central canal. A further discussion of the spinal cord can be found in Chapter 2.
+
+Meninges
+The meninges (Fig. 1.33) are three connective tissue cover-ings that surround, protect, and suspend the brain and spinal cord within the cranial cavity and vertebral canal, respectively:
+
+
+■     The dura mater is the thickest and most external of the coverings.
+■     The arachnoid mater is against the internal surface of the dura mater.
+■     The pia mater is adherent to the brain and spinal cord.
+
+Between the arachnoid and pia mater is the subarach-noid space, which contains CSF.
+A  further  discussion  of  the  cranial  meninges  can be found in Chapter 8 and of  the spinal meninges in Chapter 2.
+
+Functional subdivisions of the CNS
+Functionally,  the  nervous  system  can  be  divided  into somatic and visceral parts.
+
+
+
+
+
+
+
+
+Fig. 1.32  CNS and PNS.
+
+
+
+
+
+consist of an outer portion, or the gray matter, contain-ing cell bodies; an inner portion, or the white matter, made up of  axons forming tracts or pathways; and the ventricles, which are spaces filled with CSF.
+The cerebellum has two lateral lobes and a midline portion. The components of  the brainstem are classi-cally defined as the diencephalon, midbrain, pons, and medulla.  However,  in  common  usage  today,  the  term “brainstem” usually refers to the midbrain, pons, and medulla.
+
+
+
+
+Diploic vein
+
+External table Skull	Diploe
+Internal table
+Cranial  Endosteal layer dura
+mater  Meningeal layer
+
+Subarachnoid space Arachnoid mater
+Pia mater
+Cerebral artery
+
+Cerebral cortex
+
+Subdural space (potential space)
+Extradural space (potential space)
+
+
+
+A  further  discussion  of  the  brain  can  be  found  in 30	Chapter 8.
+
+
+Fig. 1.33  Arrangement of meninges in the cranial cavity.
+Body Systems  •  Nervous System	1
+
+
+
+■     The somatic part (soma, from the Greek for “body”) innervates structures (skin and most skeletal muscle) derived  from  somites  in  the  embryo,  and  is  mainly involved with receiving and responding to information from the external environment.
+■     The visceral part (viscera, from the Greek for “guts”) innervates organ systems in the body and other visceral elements, such as smooth muscle and glands, in periph-
+
+Somatic nerves arise segmentally along the developing CNS in association with somites, which are themselves arranged segmentally along each side of the neural tube (Fig. 1.34). Part of each somite (the dermatomyotome) gives rise to skeletal muscle and the dermis of the skin. As cells of  the dermatomyotome differentiate, they migrate into posterior (dorsal) and anterior (ventral) areas of the developing body:
+
+
+
+eral regions of  the body. It is concerned mainly with detecting  and  responding  to  information  from  the internal environment.
+
+Somatic part of the nervous system
+The somatic part of the nervous system consists of:
+
+
+■     Cells that migrate anteriorly give rise to muscles of the limbs and trunk (hypaxial muscles) and to the associ-ated dermis.
+■     Cells that migrate posteriorly give rise to the intrinsic muscles of the back (epaxial muscles) and the associ-ated dermis.
+
+
+
+■     nerves that carry conscious sensations from peripheral regions back to the CNS, and
+■     nerves that innervate voluntary muscles.
+
+
+Developing nerve cells within anterior regions of  the neural tube extend processes peripherally into posterior
+
+
+
+
+
+Neural crest	Epaxial muscles and dermis
+
+Notochord
+
+Neural tube
+
+
+Somite
+
+
+
+
+
+
+
+
+
+
+
+
+
+Ectoderm
+
+
+Hypaxial muscles and dermis
+
+
+
+Body cavity (coelom)
+
+Dermatomyotome
+
+Lateral plate mesoderm
+
+Intermediate mesoderm
+
+
+Endoderm
+
+Fig. 1.34  Differentiation of somites in a “tubular” embryo.	31
+The Body
+
+
+
+and anterior regions of  the differentiating dermatomyo-tome of each somite.
+Simultaneously, derivatives of  neural crest cells (cells derived from neural folds during formation of the neural tube) differentiate into neurons on each side of the neural
+
+Generally, all sensory information passes into the poste-rior aspect of the spinal cord, and all motor fibers leave anteriorly.
+Somatic sensory neurons carry information from the periphery  into  the  CNS  and  are  also  called  somatic
+
+tube  and  extend  processes  both  medially  and  laterally       sensory   afferents   or   general   somatic   afferents (Fig. 1.35):                                                                                     (GSAs). The modalities carried by these nerves include
+
+
+■     Medial processes pass into the posterior aspect of the neural tube.
+■     Lateral processes pass into the differentiating regions of the adjacent dermatomyotome.
+
+Neurons that develop from cells within the spinal cord
+
+temperature, pain, touch, and proprioception. Propriocep-tion is the sense of determining the position and movement of the musculoskeletal system detected by special receptors in muscles and tendons.
+Somatic motor fibers carry information away from the CNS to skeletal muscles and are also called somatic motor efferents or general somatic efferents (GSEs). Like
+
+
+
+are motor neurons and those that develop from neural crest cells are sensory neurons.
+Somatic  sensory  and  somatic  motor  fibers  that  are organized segmentally along the neural tube become parts of all spinal nerves and some cranial nerves.
+The clusters of sensory nerve cell bodies derived from neural crest cells and located outside the CNS form sensory ganglia.
+
+
+
+
+
+
+
+Somatic sensory neuron developing from neural crest cells
+
+somatic sensory fibers that come from the periphery, somatic motor fibers can be very long. They extend from cell bodies in the spinal cord to the muscle cells they innervate.
+
+Dermatomes
+Because cells from a specific somite develop into the dermis of  the skin in a precise location, somatic sensory fibers originally associated with that somite enter the posterior
+
+
+
+
+
+
+
+
+Epaxial (back) muscles
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Somatic motor neuron cell body in anterior region
+of neural tube
+
+
+
+Axon of motor neuron projects to muscle developing from dermatomyotome
+
+
+
+
+
+Hypaxial muscles
+
+
+
+32	Fig. 1.35  Somatic sensory and motor neurons. Blue lines indicate motor nerves and red lines indicate sensory nerves.
+Body Systems  •  Nervous System	1
+
+
+
+region of  the spinal cord at a specific level and become part of one specific spinal nerve (Fig. 1.36). Each spinal nerve therefore carries somatic sensory information from a specific area of skin on the surface of the body. A der-matome is that area of skin supplied by a single spinal cord level, or on one side, by a single spinal nerve.
+There is overlap in the distribution of dermatomes, but usually a specific region within each dermatome can be identified as an area supplied by a single spinal cord level. Testing touch in these autonomous zones in a conscious patient can be used to localize lesions to a specific spinal nerve or to a specific level in the spinal cord.
+
+
+Myotomes
+Somatic motor nerves that were originally associated with a specific somite emerge from the anterior region of the spinal cord and, together with sensory nerves from the same level, become part of  one spinal nerve. Therefore each spinal nerve carries somatic motor fibers to muscles that  originally  developed  from  the  related  somite.  A myotome is that portion of a skeletal muscle innervated by a single spinal cord level or, on one side, by a single spinal nerve.
+
+
+
+
+
+
+
+
+C6 segment of spinal cord Spinal ganglion
+
+Caudal
+
+Somite
+
+
+
+Dermatomyotome
+
+Cranial
+
+
+
+
+
+
+
+Autonomous region (where overlap of dermatomes is least likely)
+of C6 dermatome (pad of thumb)
+
+
+
+
+
+
+Skin on the lateral side of the forearm and on the thumb is innervated by C6 spinal level (spinal nerve).
+The dermis of the skin in this region develops from the somite initially associated with the C6 level of the developing spinal cord
+
+
+
+Fig. 1.36  Dermatomes.	33
+The Body
+
+
+
+Myotomes are generally more difficult to test than der-matomes because each skeletal muscle in the body often
+
+■     Muscles in the hand are innervated mainly by spinal nerves from spinal cord levels C8 and T1.
+
+
+
+develops  from  more  than  one  somite  and  is  therefore innervated by nerves derived from more than one spinal cord level (Fig. 1.37).
+Testing movements at successive joints can help in local-
+
+
+Visceral part of the nervous system
+The visceral part of the nervous system, as in the somatic part, consists of motor and sensory components:
+
+
+
+izing lesions to specific nerves or to a specific spinal cord level. For example:
+
+
+■     Sensory nerves monitor changes in the viscera.
+■     Motor nerves mainly innervate smooth muscle, cardiac
+
+
+
+■     Muscles that move the shoulder joint are innervated mainly  by  spinal  nerves  from  spinal  cord  levels  C5 and C6.
+■     Muscles that move the elbow are innervated mainly by spinal nerves from spinal cord levels C6 and C7.
+
+muscle, and glands.
+
+The visceral motor component is commonly referred to as the autonomic division of the PNS and is subdivided into sympathetic and parasympathetic parts.
+
+
+
+
+C6 segment of spinal cord
+
+C5 segment of spinal cord
+
+Somite
+
+
+
+
+
+
+
+
+
+Dermatomyotome
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Muscles that abduct the arm are innervated by C5 and C6 spinal levels (spinal nerves) and develop from somites initially associated with C5 and C6 regions of developing spinal cord
+
+
+
+
+34	Fig. 1.37  Myotomes.
+Body Systems  •  Nervous System	1
+
+
+
+In the clinic
+
+Dermatomes and myotomes
+A knowledge of dermatomes and myotomes is absolutely fundamental to carrying out a neurological examination. A typical dermatome map is shown in Fig. 1.38.
+Clinically, a dermatome is that area of skin supplied by a single spinal nerve or spinal cord level. A myotome is that
+
+
+
+region of skeletal muscle innervated by a single spinal nerve or spinal cord level. Most individual muscles of the body are innervated by more than one spinal cord level, so the evaluation of myotomes is usually accomplished by testing movements of joints or muscle groups.
+
+
+
+
+
+
+Cranial nerve [V] (Trigeminal nerve)
+
+V1
+[V1]
+C2
+[V2]
+
+
+
+[V3]
+C2
+C3 C4
+C5	T2
+
+T3
+
+T2	T4
+T5
+T6 T7 T8
+T1	T9
+T10
+T11	C6
+
+T12
+
+C6	L1
+C7	C8	C7
+
+
+
+
+C4
+
+C5
+
+T2
+
+
+
+T1
+
+
+
+
+
+C8
+
+C3
+
+
+T2 T3
+T4 T5 T6 T7 T8 T9 T10
+T11
+T12 L1
+L2 L3 L4 L5
+S3
+
+S4
+
+
+L2
+
+
+L3	S2
+
+L3
+
+L4
+
+L5
+L5 L4
+
+
+
+S1	S1
+
+A	B
+
+Fig. 1.38  Dermatomes. A. Anterior view. B. Posterior view.
+
+
+
+
+35
+The Body
+
+
+
+Like the somatic part of the nervous system, the visceral part is segmentally arranged and develops in a parallel fashion (Fig. 1.39).
+Visceral sensory neurons that arise from neural crest cells send processes medially into the adjacent neural tube and laterally into regions associated with the developing body. These sensory neurons and their processes, referred to as general visceral afferent fibers (GVAs), are associ-ated primarily with chemoreception, mechanoreception, and stretch reception.
+Visceral motor neurons that arise from cells in lateral regions of the neural tube send processes out of the ante-rior aspect of the tube. Unlike in the somatic part, these
+
+processes, containing general visceral efferent fibers (GVEs), synapse with other cells, usually other visceral motor neurons, that develop outside the CNS from neural crest cells that migrate away from their original positions close to the developing neural tube.
+The visceral motor neurons located in the spinal cord are referred to as preganglionic motor neurons and their axons are called preganglionic fibers; the visceral motor neurons located outside the CNS are referred to as postganglionic motor neurons and their axons are called postganglionic fibers. The cell bodies of the visceral motor neurons outside the CNS often associate with each other in a discrete mass
+called a ganglion.
+
+
+Part of neural crest developing Visceral motor ganglion	into spinal ganglia
+
+Visceral sensory neuron develops from neural crest and becomes part of spinal ganglion
+
+
+
+
+
+
+
+
+
+
+
+
+Visceral motor preganglionic neuron in lateral region of CNS (spinal cord)
+
+
+Body cavity (coelom)
+
+
+Motor nerve ending associated with blood vessels, sweat glands, arrector pili muscles at periphery
+
+Sensory nerve ending
+
+Motor nerve ending associated with viscera
+
+Postganglionic motor neuron is outside CNS.	Developing gastrointestinal tract An aggregation of postganglionic neuronal cell
+bodies forms a peripheral visceral motor ganglion.
+
+36	Fig. 1.39  Development of the visceral part of the nervous system.
+Body Systems  •  Nervous System	1
+
+
+Visceral sensory and motor fibers enter and leave the	■     The   sympathetic   system   innervates   structures   in
+
+CNS with their somatic equivalents (Fig. 1.40). Visceral sensory fibers enter the spinal cord together with somatic sensory fibers through posterior roots of  spinal nerves.
+
+peripheral regions of the body and viscera.
+■     The parasympathetic system is more restricted to inner-vation of the viscera only.
+
+
+
+Preganglionic fibers of  visceral motor neurons exit the spinal cord in the anterior roots of  spinal nerves, along with fibers from somatic motor neurons.
+Postganglionic fibers traveling to visceral elements in the periphery are found in the posterior and anterior rami (branches) of spinal nerves.
+Visceral motor and sensory fibers that travel to and from viscera form named visceral branches that are separate from the somatic branches. These nerves generally form plexuses from which arise branches to the viscera.
+Visceral motor and sensory fibers do not enter and leave the CNS at all levels (Fig. 1.41):
+
+
+Terminology
+Spinal sympathetic and spinal parasympathetic neurons share  certain  developmental  and  phenotypic  features that are different from those of cranial parasympathetic neurons. Based on this, some researchers have suggested reclassifying all spinal visceral motor neurons as sympa-thetic (Espinosa-Medina I et al. Science 2016;354:893-897). Others are against reclassification, arguing that the results only indicate that the neurons are spinal in origin
+
+
+
+■     In the cranial region, visceral components are associ-ated with four of the twelve cranial nerves (CN III, VII, IX, and X).
+■     In the spinal cord, visceral components are associated mainly with spinal cord levels T1 to L2 and S2 to S4.
+
+Visceral motor components associated with spinal levels
+
+
+
+
+
+Brainstem cranial nerves III, VII, IX, X
+
+T1 to L2 are termed sympathetic. Those visceral motor components in cranial and sacral regions, on either side of the sympathetic region, are termed parasympathetic:
+
+
+
+Somatic sensory and visceral sensory fibers
+
+
+Posterior root (sensory)
+
+Spinal ganglion
+
+Spinal nerve
+
+Posterior	Parasympathetic ramus
+
+
+
+
+
+
+
+
+Sympathetic
+
+T1 to L2
+spinal segments
+
+
+
+
+
+
+Somatic motor and visceral motor fibers
+
+Anterior root (motor)
+
+
+
+Anterior ramus
+
+
+
+
+S2 to S4 spinal segments
+
+
+
+
+
+
+
+
+Fig. 1.41  Parts of the CNS associated with visceral motor
+Fig. 1.40  Basic anatomy of a thoracic spinal nerve.	components.	37
+The Body
+Esophageal  plexus
+
+
+
+(Neuhuber W et al. Anat Rec 2017;300:1369-1370). In addition, sacral nerves do not enter the sympathetic trunk, nor do they have postganglionic fibers that travel to the periphery on spinal nerves, as do T1-L2 visceral motor fibers. We have chosen to retain the classification of S2,3,4 visceral motor neurons as parasympathetic. “Parasympa-thetic” simply means on either side of the “sympathetic,” which correctly describes their anatomy.
+
+
+
+
+Peripheral
+
+Sympathetic system
+The sympathetic part of the autonomic division of the PNS leaves  thoracolumbar  regions  of  the  spinal  cord  with the somatic components of  spinal nerves T1 to L2 (Fig. 1.42). On each side, a paravertebral sympathetic trunk extends from the base of the skull to the inferior end of the vertebral column where the two trunks converge anteriorly to the coccyx at the ganglion impar. Each trunk is attached
+
+
+
+
+Organs
+
+
+
+
+
+
+
+
+
+
+Sympathetic nerves follow somatic nerves to periphery (glands, smooth muscle)
+
+
+
+
+
+
+
+
+Heart
+
+
+
+
+
+
+
+
+
+
+
+
+Abdominal viscera
+Prevertebral plexus
+
+
+
+
+
+
+
+
+
+Ganglion impar	Pelvic viscera 38	Fig. 1.42  Sympathetic part of the autonomic division of the PNS.
+Body Systems  •  Nervous System	1
+
+
+
+to the anterior rami of spinal nerves and becomes the route by which sympathetics are distributed to the periphery and all viscera.
+Visceral motor preganglionic fibers leave the T1 to L2 part of the spinal cord in anterior roots. The fibers then enter the spinal nerves, pass through the anterior rami and into the sympathetic trunks. One trunk is located on each side of the vertebral column (paravertebral) and positioned anterior to the anterior rami. Along the trunk is a series of segmentally arranged ganglia formed from collections of postganglionic neuronal cell bodies where the pregangli-onic neurons synapse with postganglionic neurons. Ante-rior rami of T1 to L2 are connected to the sympathetic trunk or to a ganglion by a white ramus communicans, which carries preganglionic sympathetic fibers and appears white because the fibers it contains are myelinated.
+Preganglionic sympathetic fibers that enter a paraverte-bral ganglion or the sympathetic trunk through a white
+
+ramus communicans may take the following four pathways to target tissues:
+
+1.  Peripheral sympathetic innervation at the level of origin of the preganglionic fiber
+Preganglionic sympathetic fibers may synapse with post-ganglionic motor neurons in ganglia associated with the sympathetic trunk, after which postganglionic fibers enter the same anterior ramus and are distributed with periph-eral branches of the posterior and anterior rami of that spinal nerve (Fig. 1.43). The fibers innervate structures at the periphery of the body in regions supplied by the spinal nerve.  The  gray  ramus  communicans  connects  the sympathetic trunk or a ganglion to the anterior ramus and contains the postganglionic sympathetic fibers. It appears gray because postganglionic fibers are nonmyelinated. The gray ramus communicans is positioned medial to the white ramus communicans.
+
+
+
+
+T10 spinal nerve
+
+Posterior ramus
+
+
+T10 spinal segment
+
+
+
+
+
+
+
+
+Gray ramus communicans
+
+
+White ramus communicans
+
+
+
+
+
+Peripheral distribution of sympathetics carried peripherally by terminal cutaneous branches of spinal nerve T1 to L2
+
+Anterior ramus
+
+
+Motor nerve to sweat glands, smooth muscle of blood vessels, and arrector pili muscles in the part of T10 dermatome supplied by the anterior ramus
+
+
+
+Fig. 1.43  Course of sympathetic fibers that travel to the periphery in the same spinal nerves in which they travel out of the spinal cord.	39
+The Body
+
+
+
+(C1) C2 to C8
+Posterior root
+
+
+
+Anterior root
+
+
+
+Peripheral distribution of ascending sympathetics
+
+Gray ramus communicans
+
+T1 to L2
+
+
+
+
+
+
+
+Gray ramus communicans
+
+L3 to Co
+
+White ramus communicans
+
+Peripheral distribution of descending sympathetics
+
+
+Gray ramus communicans
+
+Sympathetic paravertebral trunks
+
+
+
+
+Fig. 1.44  Course of sympathetic nerves that travel to the periphery in spinal nerves that are not the ones through which they left the spinal cord.
+
+
+
+
+
+
+
+2.  Peripheral sympathetic innervation above or below the level of origin of the preganglionic fiber
+
+Preganglionic sympathetic fibers may ascend or descend to other vertebral levels where they synapse in ganglia associ-ated with spinal nerves that may or may not have visceral motor input directly from the spinal cord (i.e., those nerves other than T1 to L2) (Fig. 1.44).
+
+division of the PNS, which ultimately emerge from only a small region of the spinal cord (T1 to L2), to be distributed to peripheral regions innervated by all spinal nerves.
+White rami communicantes only occur in association with spinal nerves T1 to L2, whereas gray rami communi-cantes are associated with all spinal nerves.
+Fibers from spinal cord levels T1 to T5 pass predomi-nantly superiorly, whereas fibers from T5 to L2 pass inferi-
+
+The postganglionic fibers leave the distant ganglia via	orly.   All   sympathetics   passing   into   the   head   have
+
+gray rami communicantes and are distributed along the posterior and anterior rami of the spinal nerves.
+The ascending and descending fibers, together with all the ganglia, form the paravertebral sympathetic trunk, which extends the entire length of the vertebral column. The formation of this trunk, on each side, enables visceral
+40	motor fibers of  the sympathetic part of  the autonomic
+
+preganglionic fibers that emerge from spinal cord level T1 and ascend in the sympathetic trunks to the highest ganglion in the neck (the superior cervical ganglion), where they synapse. Postganglionic fibers then travel along blood vessels to target tissues in the head, including blood vessels, sweat glands, small smooth muscles associated with the upper eyelids, and the dilator of the pupil.
+Body Systems  •  Nervous System	1
+
+
+
+
+3.  Sympathetic innervation of thoracic and cervical viscera
+Preganglionic sympathetic fibers may synapse with post-ganglionic motor neurons in ganglia and then leave the ganglia medially to innervate thoracic or cervical viscera (Fig. 1.45). They may ascend in the trunk before synaps-ing, and after synapsing the postganglionic fibers may
+
+combine with those from other levels to form named vis-ceral nerves, such as cardiac nerves. Often, these nerves join branches from the parasympathetic system to form plexuses on or near the surface of  the target organ, for example, the cardiac and pulmonary plexuses. Branches of  the plexus innervate the organ. Spinal cord levels T1 to T5  mainly  innervate  cranial,  cervical,  and  thoracic viscera.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Cervical
+
+Sympathetic cardiac nerves	Sympathetic trunk
+
+Gray ramus communicans
+
+
+
+
+
+
+T1 to T4
+
+
+White ramus communicans
+
+Cardiac plexus
+Sympathetic cardiac nerves
+
+
+
+Fig. 1.45  Course of sympathetic nerves traveling to the heart.
+
+
+
+
+
+
+
+
+
+
+41
+The Body
+
+
+
+
+4.  Sympathetic innervation of the abdomen and pelvic regions and the adrenals
+Preganglionic sympathetic fibers may pass through the sympathetic  trunk  and  paravertebral  ganglia  without synapsing and, together with similar fibers from other levels, form splanchnic nerves (greater, lesser, least,
+
+
+
+
+
+
+
+
+
+
+Greater splanchnic nerves
+
+lumbar, and sacral), which pass into the abdomen and pelvic regions (Fig. 1.46). The preganglionic fibers in these nerves are derived from spinal cord levels T5 to L2.
+The splanchnic nerves generally connect with sympa-thetic ganglia around the roots of  major arteries that branch from the abdominal aorta. These ganglia are part of a large prevertebral plexus that also has input from the
+
+
+
+
+
+
+
+
+
+
+T5 to T9
+
+
+
+
+
+Lesser splanchnic nerves
+T9 to T10 (T10 to T11)
+
+
+Least splanchnic nerves
+
+
+T12 Lumbar splanchnic nerves
+
+
+
+
+L1 to L2
+
+
+
+
+
+Prevertebral plexus Aorta	and ganglia
+
+White ramus communicans
+
+Gray ramus communicans
+
+
+
+
+
+Abdominal and
+pelvic viscera
+
+Paravertebral sympathetic trunk
+
+
+
+
+
+Sacral splanchnic nerves
+
+
+42	Fig. 1.46  Course of sympathetic nerves traveling to abdominal and pelvic viscera.
+Body Systems  •  Nervous System	1
+Prevertebral plexus
+
+
+
+parasympathetic part of  the autonomic division of  the PNS. Postganglionic sympathetic fibers are distributed in extensions of this plexus, predominantly along arteries, to viscera in the abdomen and pelvis.
+Some of  the preganglionic fibers in the prevertebral plexus do not synapse in the sympathetic ganglia of the plexus but pass through the system to the adrenal gland, where  they  synapse  directly  with  cells  of  the  adrenal
+
+
+[III]
+
+medulla. These cells are homologues of sympathetic post-ganglionic neurons and secrete adrenaline and noradrena-line into the vascular system.
+
+Parasympathetic system
+The parasympathetic part of the autonomic division of the PNS (Fig. 1.47) leaves cranial and sacral regions of  the CNS in association with:
+
+
+Lacrimal gland
+
+
+Ciliary ganglion	Pupillary constriction
+
+
+Pterygopalatine ganglion
+[VII]	[IX]
+
+Otic ganglion
+
+
+Parotid gland
+
+
+
+Salivary glands
+
+
+
+[X]
+
+Cranial parasympathetic outflow via cranial nerves
+
+
+Submandibular ganglion
+
+
+
+
+
+
+
+
+
+Heart
+Thoracic visceral  plexus
+
+Transition from supply by [X] to pelvic splanchnic nerves
+
+
+
+
+
+
+Sacral parasympathetic outflow via pelvic splanchnic nerves
+
+
+
+Synapse with nerve cells Abdominal viscera	of enteric system
+
+
+
+
+
+S2 to S4
+
+
+Erectile tissues of penis and clitoris
+
+Pelvic viscera
+
+Fig. 1.47  Parasympathetic part of the autonomic division of the PNS.	43
+The Body
+
+
+■     cranial  nerves  III,  VII,  IX,  and  X:  III,  VII,  and  IX	The vagus nerve [X] gives rise to visceral branches along carry  parasympathetic  fibers  to  structures  within       its course. These branches contribute to plexuses associ-the  head  and  neck  only,  whereas  X  (the  vagus       ated with thoracic viscera or to the large prevertebral
+
+nerve) also innervates thoracic and most abdominal viscera; and
+■     spinal nerves S2 to S4: sacral parasympathetic fibers innervate inferior abdominal viscera, pelvic viscera, and
+
+plexus in the abdomen and pelvis. Many of these plexuses also contain sympathetic fibers.
+When present, postganglionic parasympathetic neurons are in the walls of the target viscera.
+
+the  arteries  associated  with  erectile  tissues  of  the perineum.
+
+
+Visceral sensory innervation (visceral afferents)
+
+Visceral  sensory  fibers  generally  accompany  visceral
+
+Like the visceral motor nerves of the sympathetic part, the visceral motor nerves of  the parasympathetic part generally have two neurons in the pathway. The pregangli-onic neurons are in the CNS, and fibers leave in the cranial nerves.
+
+Sacral preganglionic parasympathetic fibers
+In the sacral region, the preganglionic parasympathetic fibers form special visceral nerves (the pelvic splanchnic nerves), which originate from the anterior rami of S2 to S4 and enter pelvic extensions of  the large prevertebral plexus formed around the abdominal aorta. These fibers are distributed to pelvic and abdominal viscera mainly along blood vessels. The postganglionic motor neurons are in the walls of the viscera. In organs of the gastrointestinal system, preganglionic fibers do not have a postganglionic parasympathetic motor neuron in the pathway; instead, preganglionic fibers synapse directly on neurons in the ganglia of the enteric system.
+
+Cranial nerve preganglionic parasympathetic fibers
+The preganglionic parasympathetic motor fibers in CN III, VII, and IX separate from the nerves and connect with one of four distinct ganglia, which house postgangli-onic motor neurons. These four ganglia are near major branches of CN V. Postganglionic fibers leave the ganglia, join the branches of CN V, and are carried to target tissues (salivary, mucous, and lacrimal glands; constrictor muscle
+
+motor fibers.
+
+Visceral sensory fibers accompany sympathetic fibers
+Visceral sensory fibers follow the course of  sympathetic fibers entering the spinal cord at similar spinal cord levels. However, visceral sensory fibers may also enter the spinal cord  at  levels  other  than  those  associated  with  motor output. For example, visceral sensory fibers from the heart may enter at levels higher than spinal cord level T1. Vis-ceral sensory fibers that accompany sympathetic fibers are mainly concerned with detecting pain.
+
+Visceral sensory fibers accompany parasympathetic fibers
+Visceral  sensory  fibers  accompanying  parasympathetic fibers are carried mainly in IX and X and in spinal nerves S2 to S4.
+Visceral sensory fibers in IX carry information from chemoreceptors  and  baroreceptors  associated  with  the walls of major arteries in the neck, and from receptors in the pharynx.
+Visceral sensory fibers in X include those from cervical viscera, and major vessels and viscera in the thorax and abdomen.
+Visceral sensory fibers from pelvic viscera and the distal parts of the colon are carried in S2 to S4.
+Visceral sensory fibers associated with parasympathetic fibers primarily relay information to the CNS about the
+
+of  the pupil; and ciliary muscle in the eye) with these	status   of   normal   physiological   processes   and   reflex branches.	activities.
+
+
+
+
+
+
+
+
+
+
+
+44
+Body Systems  •  Nervous System	1
+
+
+
+Preganglionic sympathetic
+
+
+Postganglionic sympathetic
+
+Preganglionic parasympathetic
+
+Visceral afferent
+
+
+Vagal afferent
+
+
+Prevertebral sympathetic ganglion
+
+Blood vessel
+
+
+Mesentery
+
+
+
+
+Longitudinal muscle layer
+
+
+
+Circular muscle layer
+
+
+
+
+
+
+
+
+
+Peritoneum
+
+
+
+Myenteric plexus
+Submucosa muscle		Enteric nervous system Submucous plexus
+
+Submucosa
+
+Fig. 1.48  Enteric part of the nervous system.
+
+
+
+
+
+The enteric system
+The enteric nervous system consists of motor and sensory neurons and their support cells, which form two intercon-nected plexuses, the myenteric and submucous nerve
+
+
+■     bundles of nerve fibers, which pass between ganglia and from the ganglia into surrounding tissues.
+
+Neurons in the enteric system are derived from neural
+
+
+
+plexuses, within the walls of  the gastrointestinal tract (Fig. 1.48). Each of these plexuses is formed by:
+
+crest cells originally associated with occipitocervical and sacral regions. Interestingly, more neurons are reported to be in the enteric system than in the spinal cord itself.
+
+■     ganglia, which house the nerve cell bodies and associ-ated cells, and
+
+Sensory and motor neurons within the enteric system control reflex activity within and between parts of  the
+
+
+
+45
+The Body
+
+
+
+gastrointestinal system. These reflexes regulate peristalsis, secretomotor activity, and vascular tone. These activities can occur independently of the brain and spinal cord, but can also be modified by input from preganglionic parasym-pathetic and postganglionic sympathetic fibers.
+Sensory information from the enteric system is carried back to the CNS by visceral sensory fibers.
+
+Nerve plexuses
+Nerve plexuses are either somatic or visceral and combine fibers from different sources or levels to form new nerves with specific targets or destinations (Fig. 1.49). Plexuses of the enteric system also generate reflex activity independent of the CNS.
+
+Somatic plexuses
+Major somatic plexuses formed from the anterior rami of spinal nerves are the cervical (C1 to C4), brachial (C5 to T1), lumbar (L1 to L4), sacral (L4 to S4), and coccygeal (S5 to Co) plexuses. Except for spinal nerve T1, the anterior rami of thoracic spinal nerves remain independent and do not participate in plexuses.
+
+Visceral plexuses
+Visceral nerve plexuses are formed in association with viscera and generally contain efferent (sympathetic and parasympathetic)  and  afferent  components  (Fig.  1.49). These plexuses include cardiac and pulmonary plexuses in the thorax and a large prevertebral plexus in the abdomen anterior to the aorta, which extends inferiorly onto the lateral walls of the pelvis. The massive prevertebral plexus supplies input to and receives output from all abdominal and pelvic viscera.
+
+
+In the clinic
+
+Referred pain
+Referred pain occurs when sensory information comes to the spinal cord from one location but is interpreted by the CNS as coming from another location innervated by the same spinal cord level. Usually, this happens when the pain information comes from a region, such as the gut, which has a low amount of sensory output. These afferents converge on neurons at the same spinal cord level that receive information from the skin, which is an area with a high amount of sensory output. As a result, pain from the normally low output region is interpreted as coming from the normally high output region.
+Pain is most often referred from a region innervated by the visceral part of the nervous system to a region innervated, at the same spinal cord level, by the somatic side of the nervous system.
+Pain can also be referred from one somatic region to another. For example, irritation of the peritoneum on the inferior surface of the diaphragm, which is innervated by the phrenic nerve, can be referred to
+the skin on the top of the shoulder, which is innervated by other somatic nerves arising at the same spinal
+cord level.
+
+
+
+
+OTHER SYSTEMS
+
+Specific information about the organization and compo-nents of  the respiratory, gastrointestinal, and urogenital systems will be discussed in each of the succeeding chapters of this text.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+46
+Body Systems  •  Other Systems	1
+
+
+
+SOMATIC PLEXUSES
+C1
+
+C2
+
+C3
+Cervical plexus                            C4 anterior rami C1 to C4                            C5
+C6
+C7
+C8
+
+T1
+
+Brachial plexus	T2 anterior rami C5 to T1
+
+T3
+
+VISCERAL PLEXUSES
+
+Parasympathetic [X]
+
+
+
+Cardiac branches
+
+
+
+Pulmonary branch
+
+
+Cardiac plexus
+
+
+T4
+
+Pulmonary branches T5
+
+T6
+
+T7	Esophageal plexus
+
+T8	Thoracic aortic plexus
+
+T9
+
+
+
+
+
+Splanchnic nerves
+
+T10	Vagal trunk
+Greater T11
+
+Lesser T12
+
+Least L1
+
+
+L2	Prevertebral plexus
+
+L3
+
+
+
+Lumbar plexus anterior rami L1 to L4
+
+L4
+
+L5	Lumbar splanchnic nerves
+
+
+
+
+
+
+
+
+Sacral plexus anterior rami L4 to S4
+
+S1
+S2
+S3
+
+S4 S5
+
+
+
+
+Ganglion impar
+
+
+
+
+
+
+
+Sacral splanchnic nerves
+
+S2 to S4 pelvic splanchnic nerves (parasympathetic)
+
+
+Fig. 1.49  Nerve plexuses.
+47
+The Body
+
+
+Clinical cases
+
+
+Case 1 APPENDICITIS
+A young man sought medical care because of central abdominal pain that was diffuse and colicky. After some hours, the pain began to localize in the right iliac fossa and became constant. He was referred to an abdominal surgeon, who removed a grossly inflamed appendix. The patient made an uneventful recovery.
+
+When the appendix becomes inflamed, the visceral sensory fibers are stimulated. These fibers enter the spinal cord with the sympathetic fibers at spinal cord level T10. The pain is referred to the dermatome of T10, which is in the umbilical region (Fig. 1.50). The pain is diffuse, not focal; every time a peristaltic wave passes through the ileocecal region, the pain recurs. This intermittent type of pain is referred to as colic.
+
+In the later stages of the disease, the appendix contacts and irritates the parietal peritoneum in the right iliac fossa, which is innervated by somatic sensory nerves. This produces a constant focal pain, which predominates over the colicky pain that the patient felt some hours previously. The patient no longer interprets the referred pain from the T10 dermatome.
+
+
+
+
+
+
+
+
+
+
+Pain interpreted as originating in distribution of somatic sensory nerves
+
+
+
+
+
+
+
+
+
+Visceral sensory nerve
+
+
+
+Although this is a typical history for appendicitis, it should always be borne in mind that the patient’s symptoms and signs may vary. The appendix is situated in a retrocecal position in approximately 70% of patients; therefore it may never contact the parietal peritoneum anteriorly in the right iliac fossa. It is also possible that the appendix is long and may directly contact other structures. As a consequence, the patient may have other symptoms (e.g., the appendix may contact the ureter, and the patient may then develop urological symptoms).
+
+
+
+
+
+Somatic sensory nerve
+
+
+
+
+
+Appendix
+
+
+
+Patient perceives diffuse pain in T10 dermatome
+
+
+
+Although appendicitis is common, other disorders, for example of the bowel and pelvis, may produce similar symptoms.
+
+
+
+Fig. 1.50  Mechanism for referred pain from an inflamed appendix to the T10 dermatome.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+48
+Conceptual Overview  •  General Description	2
+
+
+Conceptual overview GENERAL DESCRIPTION
+
+
+The back consists of the posterior aspect of the body and provides the musculoskeletal axis of support for the trunk. Bony elements consist mainly of the vertebrae, although proximal elements of the ribs, superior aspects of the pelvic bones, and posterior basal regions of the skull contribute to the back’s skeletal framework (Fig. 2.1).
+
+Associated muscles interconnect the vertebrae and ribs with each other and with the pelvis and skull. The back contains the spinal cord and proximal parts of the spinal nerves, which send and receive information to and from most of the body.
+
+
+
+
+
+
+
+Skull
+
+
+
+
+
+Vertebra
+
+
+
+Scapula
+
+
+
+
+
+
+
+
+Vertebral column
+
+Pelvic bone
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.1  Skeletal framework of the back.	51
+Back
+
+
+FUNCTIONS	Early embryo Support
+The   skeletal   and   muscular   elements   of   the   back support the body’s weight, transmit forces through the pelvis to the lower limbs, carry and position the head,
+and brace and help maneuver the upper limbs. The verte-	Somites bral column is positioned posteriorly in the body at the
+midline. When viewed laterally, it has a number of curva-tures (Fig. 2.2):
+
+
+■     The  primary  curvature  of  the  vertebral  column  is concave anteriorly, reflecting the original shape of the embryo,  and  is  retained  in  the  thoracic  and  sacral regions in adults.
+■     Secondary curvatures, which are concave posteriorly, form in the cervical and lumbar regions and bring the center of gravity into a vertical line, which allows the body’s weight to be balanced on the vertebral column in a way that expends the least amount of muscular energy to maintain an upright bipedal stance.
+
+As stresses on the back increase from the cervical to
+
+
+Concave primary curvature of back
+
+
+
+
+Adult
+
+
+
+
+
+Cervical curvature (secondary curvature)
+
+
+
+lumbar regions, lower back problems are common.
+
+Movement
+Muscles  of  the  back  consist  of  extrinsic  and  intrinsic groups:
+
+
+
+Thoracic curvature (primary curvature)
+
+
+
+■     The extrinsic muscles of the back move the upper limbs and the ribs.
+■     The intrinsic muscles of the back maintain posture and move the vertebral column; these movements include flexion  (anterior  bending),  extension,  lateral  flexion, and rotation (Fig. 2.3).
+
+
+Lumbar curvature (secondary curvature)
+
+Sacral/coccygeal curvature (primary curvature)
+
+
+Although the amount of movement between any two vertebrae is limited, the effects between vertebrae are addi-
+tive along the length of the vertebral column. Also, freedom	Gravity line of  movement and extension are limited in the thoracic
+region relative to the lumbar part of the vertebral column. Muscles in more anterior regions flex the vertebral column.
+
+
+
+
+
+
+
+
+
+
+52	Fig. 2.2  Curvatures of the vertebral column.
+Conceptual Overview  •  Functions	2
+
+
+Extension	Flexion	Lateral flexion	Rotation
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.3  Back movements.
+
+
+
+
+
+In the cervical region, the first two vertebrae and associ-ated muscles are specifically modified to support and posi-tion the head. The head flexes and extends, in the nodding motion, on vertebra CI, and rotation of the head occurs as vertebra CI moves on vertebra CII (Fig. 2.3).
+
+Protection of the nervous system
+The vertebral column and associated soft tissues of  the back contain the spinal cord and proximal parts of  the spinal nerves (Fig. 2.4). The more distal parts of the spinal nerves pass into all other regions of the body, including certain regions of the head.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.4  Nervous system.
+
+Brain
+
+Cranial nerve
+
+
+Spinal cord
+
+Spinal nerve
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+53
+Back
+
+
+
+COMPONENT PARTS Bones
+The major bones of  the back are the 33 vertebrae (Fig. 2.5). The number and specific characteristics of the verte-brae vary depending on the body region with which they
+
+are associated. There are seven cervical, twelve thoracic, five lumbar, five sacral, and three to four coccygeal verte-brae. The sacral vertebrae fuse into a single bony element, the sacrum. The coccygeal vertebrae are rudimentary in structure, vary in number from three to four, and often fuse into a single coccyx.
+
+
+
+
+
+
+
+
+
+
+
+
+
+7 cervical vertebrae (CI–CVII)
+
+
+
+
+
+
+
+
+
+12 thoracic vertebrae (TI–TXII)
+
+
+
+
+
+
+
+
+
+5 lumbar vertebrae (LI–LV)
+
+
+
+
+Sacrum
+(5 fused sacral vertebrae I-V)
+
+Coccyx
+(3–4 fused coccygeal vertebrae I-IV)
+
+
+
+
+
+
+
+
+54	Fig. 2.5  Vertebrae.
+Conceptual Overview  •  Component Parts	2
+
+
+
+
+Typical vertebra
+A typical vertebra consists of a vertebral body and a verte-bral arch (Fig. 2.6).
+The vertebral body is anterior and is the major weight-
+
+On each side of the vertebral arch, a transverse process extends laterally from the region where a lamina meets a pedicle. From the same region, a superior articular process and an inferior articular process articulate with similar processes on adjacent vertebrae.
+
+bearing  component  of  the  bone.  It  increases  in  size	Each vertebra also contains rib elements. In the thorax,
+
+from vertebra CII to vertebra LV. Fibrocartilaginous inter-vertebral discs separate the vertebral bodies of  adjacent vertebrae.
+The vertebral arch is firmly anchored to the posterior surface of the vertebral body by two pedicles, which form the lateral pillars of  the vertebral arch. The roof  of  the vertebral arch is formed by right and left laminae, which fuse at the midline.
+The vertebral arches of  the vertebrae are aligned to form the lateral and posterior walls of the vertebral canal, which extends from the first cervical vertebra (CI) to the last sacral vertebra (vertebra SV). This bony canal contains the spinal cord and its protective membranes, together with blood vessels, connective tissue, fat, and proximal parts of spinal nerves.
+The vertebral arch of a typical vertebra has a number of characteristic projections, which serve as:
+
+these costal elements are large and form ribs, which articu-late with the vertebral bodies and transverse processes. In all other regions, these rib elements are small and are incorporated into the transverse processes. Occasionally, they develop into ribs in regions other than the thorax, usually in the lower cervical and upper lumbar regions.
+
+
+Muscles
+Muscles in the back can be classified as extrinsic or intrinsic based on their embryological origin and type of innerva-tion (Fig. 2.7).
+The extrinsic muscles are involved with movements of the upper limbs and thoracic wall and, in general, are innervated by anterior rami of spinal nerves. The superfi-cial group of these muscles is related to the upper limbs, while the intermediate layer of muscles is associated with
+
+
+
+
+■     attachments for muscles and ligaments, ■     levers for the action of muscles, and
+■     sites of articulation with adjacent vertebrae.
+
+A spinous process projects posteriorly and generally
+
+the thoracic wall.
+All of  the intrinsic muscles of  the back are deep in position  and  are  innervated  by  the  posterior  rami  of spinal  nerves.  They  support  and  move  the  vertebral column and participate in moving the head. One group of  intrinsic muscles also moves the ribs relative to the
+
+inferiorly from the roof of the vertebral arch.	vertebral column.
+
+
+
+
+
+
+
+Anterior
+
+Pedicle
+
+Transverse process
+
+
+
+
+
+Vertebral body
+
+
+Superior
+
+Superior vertebral notch
+Pedicle
+
+
+Superior articular process
+
+Transverse process
+
+Spinous process
+
+
+Anterior	Posterior
+Fused costal (rib) element
+
+
+Lamina
+
+Spinous process
+
+
+Vertebral arch
+
+
+Inferior Vertebral body
+
+Lamina
+
+Inferior articular process
+
+
+A	Posterior	B	Inferior vertebral notch
+
+Fig. 2.6  A typical vertebra. A. Superior view. B. Lateral view.	55
+Back
+
+
+
+
+
+
+Levator scapulae Trapezius
+Rhomboid minor
+
+Serratus posterior superior
+
+
+
+
+Rhomboid major
+
+
+
+Latissimus dorsi
+
+Serratus posterior inferior
+
+
+
+
+
+
+
+
+
+Superficial group	Intermediate group
+
+
+
+A
+
+Extrinsic muscles
+Innervated by anterior rami of spinal nerves or cranial nerve XI (trapezius)
+
+
+
+
+
+Suboccipital	Splenius
+
+
+
+
+Longissimus
+Erector spinae          Iliocostalis Spinalis
+
+
+
+
+
+
+
+
+
+Deep group
+
+Intrinsic muscles
+B	True back muscles innervated by posterior rami of spinal nerves
+
+Fig. 2.7  Back muscles. A. Extrinsic muscles. B. Intrinsic muscles.
+
+
+
+56
+Conceptual Overview  •  Component Parts	2
+
+Vertebral canal                                                                     ■     The  pia  mater  is  the  innermost  membrane  and  is The spinal cord lies within a bony canal formed by adjacent           intimately   associated   with   the   surface   of    the
+
+vertebrae and soft tissue elements (the vertebral canal) (Fig. 2.8):
+
+spinal cord.
+■     The second membrane, the arachnoid mater, is sepa-
+
+
+■     The anterior wall is formed by the vertebral bodies of  the vertebrae, intervertebral discs, and associated ligaments.
+■     The lateral walls and roof are formed by the vertebral arches and ligaments.
+
+rated from the pia by the subarachnoid space, which contains cerebrospinal fluid.
+■     The thickest and most external of the membranes, the dura mater, lies directly against, but is not attached to, the arachnoid mater.
+
+In  the  vertebral  canal,  the  dura  mater  is  separated
+
+
+
+Within the vertebral canal, the spinal cord is surrounded by a series of  three connective tissue membranes (the meninges):
+
+from surrounding bone by an extradural (epidural) space containing  loose  connective  tissue,  fat,  and  a  venous plexus.
+
+
+
+
+
+Spinal cord
+
+Pia mater
+
+
+
+Anterior internal vertebral venous plexus
+
+Subarachnoid space
+
+Arachnoid mater
+
+Dura mater
+
+
+Posterior longitudinal
+ligament	Position of spinal ganglion
+
+
+
+Posterior ramus
+
+
+Extradural space	Anterior ramus
+
+Extradural fat
+
+
+Vertebral body
+
+
+Transverse Intervertebral disc	process
+
+
+
+Spinous process
+
+
+
+
+
+
+
+Fig. 2.8  Vertebral canal.	57
+Back
+
+
+
+
+
+Spinal nerves
+The 31 pairs of spinal nerves are segmental in distribution and emerge from the vertebral canal between the pedicles of  adjacent vertebrae. There are eight pairs of  cervical nerves (C1 to C8), twelve thoracic (T1 to T12), five lumbar (L1 to L5), five sacral (S1 to S5), and one coccygeal (Co).
+
+■     a posterior ramus—collectively, the small posterior rami innervate the back; and
+■     an  anterior  ramus—the  much  larger  anterior  rami innervate most other regions of  the body except the head, which is innervated predominantly, but not exclu-sively, by cranial nerves.
+
+The anterior rami form the major somatic plexuses
+
+Each nerve is attached to the spinal cord by a posterior root and an anterior root (Fig. 2.9).
+After  exiting  the  vertebral  canal,  each  spinal  nerve branches into:
+
+
+(cervical, brachial, lumbar, and sacral) of the body. Major visceral components of the PNS (sympathetic trunk and prevertebral plexus) of the body are also associated mainly with the anterior rami of spinal nerves.
+
+
+
+
+
+
+
+Prevertebral plexus
+
+
+
+Prevertebral ganglion (sympathetic)
+
+
+Aorta
+
+
+Vertebral body
+
+
+Anterior root
+Sympathetic ganglion
+
+
+Visceral components	Anterior ramus
+
+
+
+
+Posterior ramus
+
+
+Posterior root	Spinal nerve
+
+
+
+Lamina
+Extradural space
+
+
+Spinal cord	   Arachnoid mater Dura mater
+Pia mater	Subarachnoid space
+
+
+Spinous process
+
+
+
+58	Fig. 2.9  Spinal nerves (transverse section).
+Conceptual Overview  •  Relationship to Other Regions	2
+
+
+
+
+RELATIONSHIP TO OTHER REGIONS Head
+Cervical regions of  the back constitute the skeletal and much of the muscular framework of the neck, which in turn supports and moves the head (Fig. 2.10).
+
+
+
+
+
+
+
+
+
+
+
+Vertebral arteries travel in transverse processes of
+C6-C1, then pass through foramen magnum
+
+The brain and cranial meninges are continuous with the spinal cord meninges at the foramen magnum of the skull. The paired vertebral arteries ascend, one on each side, through foramina in the transverse processes of cervi-cal vertebrae and pass through the foramen magnum to participate, with the internal carotid arteries, in supplying blood to the brain.
+
+
+
+
+
+
+
+
+
+Cervical region
+• supports and moves head • transmits spinal cord and
+vertebral arteries between head and neck
+
+
+
+
+Thoracic region
+• support for thorax
+
+
+
+
+
+
+Lumbar region
+• support for abdomen
+
+Sacral region
+• transmits weight to lower limbs through pelvic bones
+• framework for posterior aspect of pelvis
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.10  Relationships of the back to other regions.	59
+Back
+
+
+
+
+Thorax, abdomen, and pelvis
+The different regions of the vertebral column contribute to the skeletal framework of the thorax, abdomen, and pelvis (Fig. 2.10). In addition to providing support for each of these parts of the body, the vertebrae provide attachments for muscles and fascia, and articulation sites for other bones. The anterior rami of spinal nerves associated with the thorax, abdomen, and pelvis pass into these parts of the body from the back.
+
+Limbs
+The bones of the back provide extensive attachments for muscles associated with anchoring and moving the upper limbs on the trunk. This is less true of  the lower limbs, which are firmly anchored to the vertebral column through articulation of  the pelvic bones with the sacrum. The upper and lower limbs are innervated by anterior rami of spinal nerves that emerge from cervical and lumbosacral levels, respectively, of the vertebral column.
+
+KEY FEATURES
+Long vertebral column and short spinal cord
+
+During development, the vertebral column grows much faster than the spinal cord. As a result, the spinal cord does not extend the entire length of  the vertebral canal (Fig. 2.11).
+In the adult, the spinal cord typically ends between vertebrae LI and LII, although it can end as high as vertebra TXII and as low as the disc between vertebrae LII and LIII. Spinal nerves originate from the spinal cord at increas-ingly oblique angles from vertebrae CI to Co, and the nerve roots pass in the vertebral canal for increasingly longer distances.  Their  spinal  cord  level  of   origin  therefore becomes  increasingly  dissociated  from  their  vertebral column level of exit. This is particularly evident for lumbar
+and sacral spinal nerves.
+
+
+Subarachnoid space
+
+
+Cervical enlargement (of spinal cord)
+
+
+
+
+
+Pedicles of vertebrae
+
+
+Spinal ganglion
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Lumbosacral enlargement (of spinal cord)
+
+End of spinal cord at LI–LII vertebrae
+
+
+Arachnoid mater
+
+Dura mater
+
+
+1
+
+2
+
+3
+
+4
+
+5
+
+6
+
+7
+
+8
+
+1
+
+2
+
+3
+
+4
+
+5
+
+6
+
+7
+
+8
+
+9
+
+10
+
+11
+
+12
+
+1
+
+2
+3 4
+5
+1 2
+3 4
+5 1
+
+
+
+C1
+
+C2 C3 C4
+C5 C6 C7 C8
+T1
+T2
+
+T3
+
+T4
+
+T5
+
+T6
+
+T7
+
+
+T8
+
+T9
+
+T10
+
+T11
+
+
+T12
+
+L1
+
+L2
+
+L3
+
+L4
+
+L5
+
+
+
+End of subarachnoid
+space–sacral                                                                      S1 vertebra II                                                                      S2
+S3 S4 S5
+Co
+
+
+60	Fig. 2.11  Vertebral canal, spinal cord, and spinal nerves.
+Conceptual Overview  •  Key Features	2
+
+
+
+
+Intervertebral foramina and spinal nerves
+Each spinal nerve exits the vertebral canal laterally through an  intervertebral  foramen  (Fig.  2.12). The  foramen  is formed between adjacent vertebral arches and is closely related to intervertebral joints:
+
+Any pathology that occludes or reduces the size of an intervertebral foramen, such as bone loss, herniation of the intervertebral disc, or dislocation of the zygapophysial joint (the joint between the articular processes), can affect the function of the associated spinal nerve.
+
+
+
+
+■     The superior and inferior margins are formed by notches in adjacent pedicles.
+■     The posterior margin is formed by the articular processes of the vertebral arches and the associated joint.
+■     The  anterior  border  is  formed  by  the  intervertebral
+
+Innervation of the back
+Posterior branches of spinal nerves innervate the intrinsic muscles of  the back and adjacent skin. The cutaneous distribution of these posterior rami extends into the gluteal region of the lower limb and the posterior aspect of the
+
+
+
+disc  between  the  vertebral  bodies  of   the  adjacent vertebrae.
+
+head. Parts of  dermatomes innervated by the posterior rami of spinal nerves are shown in Fig. 2.13.
+
+
+
+
+
+
+Superior articular process
+
+Joint between superior and inferior articular processes (zygapophysial joint)
+
+Superior vertebral notch Intervertebral
+foramen Spinal nerve
+
+
+C2
+
+
+C3
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Intervertebral disc
+
+Inferior articular process	Inferior vertebral notch
+S5, Co
+
+C4
+T2 T3 T4
+T5 T6 T7
+T8 T9 T10 T11
+T12 L1 L2 L3 L4
+L5
+S1 S2
+S3
+S4
+
+Fig. 2.12  Intervertebral foramina.
+
+
+
+
+
+*The dorsal rami of L4 and L5 may not have cutaneous branches and may therefore not be represented as dermatomes on the back
+
+Fig. 2.13  Dermatomes innervated by posterior rami of spinal nerves.
+
+
+61
+Back
+
+
+
+
+Regional anatomy SKELETAL FRAMEWORK
+
+Skeletal components of  the back consist mainly of  the
+
+Vertebrae
+There are approximately 33 vertebrae, which are subdi-vided into five groups based on morphology and location (Fig. 2.14):
+
+
+
+vertebrae and associated intervertebral discs. The skull, scapulae, pelvic bones, and ribs also contribute to the bony
+
+■     The seven cervical vertebrae between the thorax and skull are characterized mainly by their small size and
+
+
+
+framework  of  the  back  and  provide  sites  for  muscle attachment.
+
+the presence of a foramen in each transverse process (Figs. 2.14 and 2.15).
+
+
+
+
+
+
+
+
+
+Anterior
+
+
+Fused costal (rib) element
+
+
+Foramen transversarium
+
+
+
+7 Cervical vertebrae
+
+Cervical vertebra
+
+
+
+
+12 Thoracic vertebrae
+Rib
+
+
+
+
+Thoracic vertebra	5 Lumbar vertebrae
+
+
+Sacrum
+
+Fused costal	Coccyx (rib) element
+
+
+
+
+Lumbar vertebra
+
+
+Posterior
+
+62	Fig. 2.14  Vertebrae.
+Regional Anatomy  •  Skeletal Framework	2
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+CII
+Vertebral body of CIII
+
+
+Posterior tubercle of CI (atlas)
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A
+
+Rib II	Spinous process of CVII
+
+B
+
+Location of intervertebral disc
+
+
+
+Vertebra prominens (spinous process of CVII)
+
+
+Fig. 2.15  Radiograph of cervical region of vertebral column. A. Anteroposterior view. B. Lateral view.
+
+
+
+
+
+
+
+
+
+
+
+63
+Back
+
+
+
+■     The 12 thoracic vertebrae are characterized by their articulated  ribs  (Figs.  2.14  and  2.16);  although  all vertebrae have rib elements, these elements are small and are incorporated into the transverse processes in regions other than the thorax; but in the thorax, the ribs are separate bones and articulate via synovial joints with the vertebral bodies and transverse processes of the associated vertebrae.
+
+■     Next are five sacral vertebrae fused into one single bone called the sacrum, which articulates on each side with a pelvic bone and is a component of the pelvic wall.
+■     Inferior to the sacrum is a variable number, usually four, of coccygeal vertebrae, which fuse into a single small triangular bone called the coccyx.
+
+In the embryo, the vertebrae are formed intersegmen-
+
+■     Inferior to the thoracic vertebrae are five lumbar verte-brae, which form the skeletal support for the posterior abdominal wall and are characterized by their large size (Figs. 2.14 and 2.17).
+
+
+tally from cells called sclerotomes, which originate from adjacent somites (Fig. 2.18). Each vertebra is derived from the cranial parts of the two somites below, one on each side, and the caudal parts of the two somites above. The
+
+
+
+
+
+
+
+
+Pedicle	Vertebral body
+Location of intervertebral disc
+
+
+
+
+
+
+
+
+
+
+
+
+Rib
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A	B
+
+
+Transverse process
+Spinous process
+Location of intervertebral disc
+
+Vertebral body Intervertebral foramen
+
+
+64	Fig. 2.16  Radiograph of thoracic region of vertebral column. A. Anteroposterior view. B. Lateral view.
+Regional Anatomy  •  Skeletal Framework	2
+
+
+
+
+Transverse process
+
+Location of intervertebral disc
+
+
+
+Rib
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A
+
+Spinous process of LIV	Pedicle
+
+
+B
+
+Intervertebral foramen
+Vertebral body of LIII
+
+
+Fig. 2.17  Radiograph of lumbar region of vertebral column. A. Anteroposterior view. B. Lateral view.
+
+
+
+
+
+Developing Somites	spinal nerve
+
+
+Caudal
+
+
+Developing spinal nerve
+
+
+
+
+
+
+
+
+Neural tube
+
+Cranial
+
+Forming vertebra	Somites
+
+Migrating sclerotome cells
+Sclerotome
+
+Fig. 2.18  Development of the vertebrae.	65
+Back
+
+
+
+spinal nerves develop segmentally and pass between the forming vertebrae.
+
+The vertebral arch of each vertebra consists of pedicles and laminae (Fig. 2.19):
+
+
+
+Typical vertebra
+A typical vertebra consists of a vertebral body and a poste-rior vertebral arch (Fig. 2.19). Extending from the vertebral arch are a number of processes for muscle attachment and articulation with adjacent bone.
+The vertebral body is the weight-bearing part of the vertebra  and  is  linked  to  adjacent  vertebral  bodies  by
+
+
+■     The two pedicles are bony pillars that attach the verte-bral arch to the vertebral body.
+■     The two laminae are flat sheets of  bone that extend from each pedicle to meet in the midline and form the roof of the vertebral arch.
+
+A spinous process projects posteriorly and inferiorly
+
+
+
+intervertebral discs and ligaments. The size of  vertebral bodies increases inferiorly as the amount of weight sup-ported increases.
+The vertebral arch forms the lateral and posterior parts of the vertebral foramen.
+The vertebral foramina of  all the vertebrae together form the vertebral canal, which contains and protects the spinal cord. Superiorly, the vertebral canal is continu-ous, through the foramen magnum of the skull, with the cranial cavity of the head.
+
+from the junction of  the two laminae and is a site for muscle and ligament attachment.
+A transverse process extends posterolaterally from the junction of the pedicle and lamina on each side and is a site for muscle and ligament attachment, and for articu-lation with ribs in the thoracic region.
+Also projecting from the region where the pedicles join the laminae are superior and inferior articular processes (Fig. 2.19), which articulate with the inferior and superior articular processes, respectively, of adjacent vertebrae.
+
+
+
+
+
+
+
+
+
+Superior articular process	Superior vertebral notch
+
+
+Vertebral body
+
+
+Pedicle
+
+
+
+
+Transverse process
+
+Lamina
+
+Spinous process
+
+
+Vertebral arch
+
+
+Inferior articular process	Inferior vertebral notch
+
+
+Superior view	Superolateral oblique view
+
+Fig. 2.19  Typical vertebra.
+
+
+
+
+
+
+
+66
+Regional Anatomy  •  Skeletal Framework	2
+
+
+Between  the  vertebral  body  and  the  origin  of  the	■     The vertebral body is short in height and square shaped
+
+articular processes, each pedicle is notched on its superior and inferior surfaces. These superior and inferior ver-tebral  notches  participate  in  forming  intervertebral foramina.
+
+Cervical vertebrae
+The seven cervical vertebrae are characterized by their small size and by the presence of a foramen in each trans-
+
+when viewed from above and has a concave superior surface and a convex inferior surface.
+■     Each transverse process is trough shaped and perforated by a round foramen transversarium.
+■     The spinous process is short and bifid. ■     The vertebral foramen is triangular.
+
+The  first  and  second  cervical  vertebrae—the  atlas
+
+
+
+verse process. A typical cervical vertebra has the following features (Fig. 2.20A):
+
+
+
+
+
+
+
+
+
+
+
+Superior view
+
+and axis—are specialized to accommodate movement of the head.
+
+
+
+
+
+
+
+
+
+
+
+Anterior view
+
+
+Foramen transversarium	Vertebral body
+
+Uncinate process
+
+
+Transverse process
+
+
+
+
+Vertebral canal
+
+A
+
+
+Foramen
+Spinous process	transversarium	Spinous process
+
+
+
+
+Fig. 2.20  Regional vertebrae. A. Typical cervical vertebra.
+
+Continued
+
+
+
+
+
+
+
+
+
+
+
+
+
+67
+Back
+
+
+
+Atlas (CI vertebra)
+
+Anterior tubercle
+
+Facet for dens
+
+
+
+Impressions for alar ligaments
+
+
+
+
+Anterior arch Lateral mass
+Transverse process
+
+
+Foramen transversarium
+
+Facet for occipital condyle
+
+
+Atlas (CI vertebra) and Axis (CII vertebra)
+
+Transverse ligament of atlas
+
+Posterior arch	Posterior tubercle
+
+
+Superior view	  Tectorial membrane (upper part	Superior view of posterior longitudinal ligament)
+
+
+Apical ligament of dens
+
+
+
+Transverse ligament of atlas
+
+Dens	Inferior longitudinal
+Axis (CII vertebra)	band of cruciform
+ligament
+
+Dens
+
+Facets for attachment of alar ligaments
+
+
+Atlas (CI vertebra) and Axis (CII vertebra) and base of skull
+
+
+Alar ligaments
+
+Posterior longitudinal
+ligament
+B	Superior view	Posterior view	Posterosuperior view
+
+
+Demifacet for articulation	Vertebral body with head of its own rib
+
+
+Facet for articulation with tubercle of
+its own rib
+
+
+
+
+
+
+Transverse process
+
+
+
+Spinous process
+
+
+Demifacet for articulation with head of rib below
+
+
+Transverse process
+
+Mammillary process
+Spinous process
+
+C	Superior view	Lateral view	D	Superior view
+
+Fig. 2.20, cont’d B. Atlas and axis. C. Typical thoracic vertebra. D. Typical lumbar vertebra.
+68
+Regional Anatomy  •  Skeletal Framework	2
+
+
+
+
+
+
+
+
+Posterior sacral foramina
+
+Coccygeal cornu
+
+
+Anterior sacral foramina
+
+Facet for articulation
+with pelvic bone
+
+
+Incomplete sacral canal
+
+
+
+E	Anterior view	Dorsolateral view	F   Posterior view
+
+Fig. 2.20, cont’dE. Sacrum. F. Coccyx.
+
+
+
+
+Atlas and axis
+Vertebra CI (the atlas) articulates with the head (Fig. 2.21). Its major distinguishing feature is that it lacks a vertebral body (Fig. 2.20B). In fact, the vertebral body of CI fuses onto the body of CII during development to become the dens of CII. As a result, there is no intervertebral disc
+
+Inferior articular facet on lateral mass of CI
+
+between CI and CII. When viewed from above, the atlas is ring shaped and composed of two lateral masses inter-connected by an anterior arch and a posterior arch.
+Each lateral mass articulates above with an occipital condyle of the skull and below with the superior articular process of vertebra CII (the axis). The superior articular surfaces are bean shaped and concave, whereas the infe-rior articular surfaces are almost circular and flat.
+The atlanto-occipital joint allows the head to nod up and down on the vertebral column.
+The posterior surface of the anterior arch has an articu-lar facet for the dens, which projects superiorly from the vertebral body of the axis. The dens is held in position by a strong transverse ligament of atlas posterior to it and spanning the distance between the oval attachment facets on the medial surfaces of the lateral masses of the atlas.
+The  dens  acts  as  a  pivot  that  allows  the  atlas  and attached head to rotate on the axis, side to side.
+The transverse processes of  the atlas are large and protrude further laterally than those of the other cervical vertebrae and act as levers for muscle action, particularly for  muscles  that  move  the  head  at  the  atlanto-axial joints.
+
+The  axis  is  characterized  by  the  large  tooth-like
+
+
+
+
+
+
+
+Superior articular facet of CII
+
+dens, which extends superiorly from the vertebral body (Figs. 2.20B and 2.21). The anterior surface of the dens has an oval facet for articulation with the anterior arch of the atlas.
+The two superolateral surfaces of the dens possess cir-cular impressions that serve as attachment sites for strong
+Dens                                       alar ligaments, one on each side, which connect the dens to the medial surfaces of the occipital condyles. These alar
+
+Fig. 2.21  Radiograph showing CI (atlas) and CII (axis) vertebrae. Open mouth, anteroposterior (odontoid peg) view.
+
+
+ligaments check excessive rotation of the head and atlas relative to the axis.	69
+Back
+
+
+
+Thoracic vertebrae
+The twelve thoracic vertebrae are all characterized by their articulation with ribs. A typical thoracic vertebra has two partial facets (superior and inferior costal facets) on each side of the vertebral body for articulation with the head of its own rib and the head of the rib below (Fig. 2.20C). The superior costal facet is much larger than the inferior costal facet.
+Each transverse process also has a facet (transverse costal facet) for articulation with the tubercle of its own rib. The vertebral body of the vertebra is somewhat heart shaped when viewed from above, and the vertebral foramen is circular.
+
+Lumbar vertebrae
+The five lumbar vertebrae are distinguished from vertebrae in other regions by their large size (Fig. 2.20D). Also, they lack facets for articulation with ribs. The transverse proc-esses are generally thin and long, with the exception of those on vertebra LV, which are massive and somewhat cone shaped for the attachment of iliolumbar ligaments to connect the transverse processes to the pelvic bones.
+The vertebral body of a typical lumbar vertebra is cylin-drical and the vertebral foramen is triangular in shape and larger than in the thoracic vertebrae.
+
+Sacrum
+The sacrum is a single bone that represents the five fused sacral vertebrae (Fig. 2.20E). It is triangular in shape with the apex pointed inferiorly, and is curved so that it has a
+
+
+and below with the coccyx. It has two large L-shaped facets, one on each lateral surface, for articulation with the pelvic bones.
+The posterior surface of the sacrum has four pairs of posterior sacral foramina, and the anterior surface has four pairs of anterior sacral foramina for the passage of the posterior and anterior rami, respectively, of S1 to S4 spinal nerves.
+The posterior wall of the vertebral canal may be incom-plete near the inferior end of the sacrum.
+
+Coccyx
+The coccyx is a small triangular bone that articulates with the inferior end of the sacrum and represents three to four fused coccygeal vertebrae (Fig. 2.20F). It is characterized by its small size and by the absence of vertebral arches and therefore a vertebral canal.
+
+
+Intervertebral foramina
+Intervertebral foramina are formed on each side between adjacent parts of vertebrae and associated intervertebral discs (Fig. 2.22). The foramina allow structures, such as spinal nerves and blood vessels, to pass in and out of the vertebral canal.
+An intervertebral foramen is formed by the inferior vertebral notch on the pedicle of the vertebra above and the superior vertebral notch on the pedicle of the vertebra below. The foramen is bordered:
+
+
+
+concave anterior surface and a correspondingly convex posterior surface. It articulates above with vertebra LV
+
+■     posteriorly  by  the  zygapophysial  joint  between  the articular processes of the two vertebrae, and
+
+
+
+
+Inferior vertebral notch
+
+
+
+
+Intervertebral foramen
+
+Zygapophysial joint	Intervertebral disc
+
+
+
+
+
+
+
+Superior vertebral notch
+
+70	Fig. 2.22  Intervertebral foramen.
+Regional Anatomy  •  Skeletal Framework	2
+
+
+
+■     anteriorly by the intervertebral disc and adjacent verte-bral bodies.
+
+Each intervertebral foramen is a confined space sur-
+
+reasonably complete bony dorsal wall for the vertebral canal. However, in the lumbar region, large gaps exist between the posterior components of  adjacent vertebral arches (Fig. 2.23). These gaps between adjacent laminae
+
+
+
+rounded by bone and ligament, and by joints. Pathology in any of these structures, and in the surrounding muscles, can affect structures within the foramen.
+
+Posterior spaces between vertebral arches
+In most regions of the vertebral column, the laminae and spinous processes of adjacent vertebrae overlap to form a
+
+and  spinous  processes  become  increasingly  wide  from vertebra LI to vertebra LV. The spaces can be widened further by flexion of  the vertebral column. These gaps allow relatively easy access to the vertebral canal for clini-cal procedures.
+
+
+
+
+
+
+
+
+
+
+Thoracic vertebrae
+
+
+Lamina
+
+
+Spinous process
+
+
+
+
+
+
+Lumbar vertebrae
+Spinous process
+
+Lamina
+
+
+Space between adjacent laminae
+
+
+Fig. 2.23  Spaces between adjacent vertebral arches in the lumbar region.
+
+
+
+
+
+
+
+
+
+
+
+71
+Back
+
+
+
+In the clinic
+
+Spina bifida
+Spina bifida is a disorder in which the two sides of vertebral arches, usually in lower vertebrae, fail to fuse during development, resulting in an “open” vertebral canal (Fig. 2.24). There are two types of spina bifida.
+
+
+
+Fourth ventricle
+Thoracic aorta Brain
+
+
+
+
+Vertebral
+spinous process
+
+
+
+■     The commonest type is spina bifida occulta, in which there is a defect in the vertebral arch of LV or SI. This defect occurs in as many as 10% of individuals and results in failure of the posterior arch to fuse in the midline. Clinically, the patient is asymptomatic, although physical examination may reveal a tuft of hair over the spinous processes.
+■     The more severe form of spina bifida involves complete failure of fusion of the posterior arch at the lumbosacral junction, with a large outpouching of the meninges. This may contain cerebrospinal fluid (a meningocele) or a portion of the spinal cord (a myelomeningocele). These abnormalities may result in a variety of neurological deficits, including problems with walking and bladder function.
+
+
+
+
+
+
+Spinal
+cord
+
+
+
+Vertebral
+body
+
+Myelomeningocele
+
+
+Fig. 2.24  T1-weighted MR image in the sagittal plane demonstrating a lumbosacral myelomeningocele. There is an absence of laminae and spinous processes in the lumbosacral region.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+72
+Regional Anatomy  •  Skeletal Framework	2
+
+
+
+In the clinic
+
+Vertebroplasty
+Vertebroplasty is a relatively new technique in which the body of a vertebra can be filled with bone cement (typically methyl methacrylate). The indications for the technique include vertebral body collapse and pain from the vertebral body, which may be secondary to tumor infiltration. The procedure is most commonly performed for osteoporotic wedge fractures, which are a considerable cause of morbidity and pain in older patients.
+Osteoporotic wedge fractures (Fig. 2.25) typically occur in the thoracolumbar region, and the approach to performing vertebroplasty is novel and relatively straightforward. The procedure is performed under sedation or light general
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Wedge fracture
+
+Fig. 2.25  Radiograph of the lumbar region of the vertebral column demonstrating a wedge fracture of the L1 vertebra. This condition is typically seen in patients with osteoporosis.
+
+
+
+anesthetic. Using X-ray guidance the pedicle is identified on the anteroposterior image. A metal cannula is placed through the pedicle into the vertebral body. Liquid bone cement is injected via the cannula into the vertebral body (Fig. 2.26). The function of the bone cement is two-fold. First, it increases the strength of the vertebral body and prevents further loss of height. Furthermore, as the bone cement sets, there is a degree of heat generated that is believed to disrupt pain nerve endings. Kyphoplasty is a similar technique that aims to restore some or all of the lost vertebral body height from the wedge fracture by injecting liquid bone cement into the vertebral body.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.26  Radiograph of the lumbar region of the vertebral column demonstrating three intrapedicular needles, all of which have been placed into the middle of the vertebral bodies. The high-density material is radiopaque bone cement, which has been injected as a liquid that will harden.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+73
+Back
+
+
+
+In the clinic
+
+Scoliosis
+Scoliosis is an abnormal lateral curvature of the vertebral column (Fig. 2.27).
+A true scoliosis involves not only the curvature (right- or left-sided) but also a rotational element of one vertebra upon another.
+The commonest types of scoliosis are those for which we have little understanding about how or why they occur and are termed idiopathic scoliosis. It is thought that there is some initial axial rotation of the vertebrae, which then alters the locations of the mechanical compressive and distractive forces applied through the vertebral growth plates, leading to changes in speed of bone growth and ultimately changes to spinal curvature. These are never present at birth and tend to occur in either the infantile, juvenile, or adolescent age
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A
+
+
+
+groups. The vertebral bodies and posterior elements (pedicles and laminae) are normal in these patients.
+When a scoliosis is present from birth (congenital scoliosis) it is usually associated with other developmental abnormalities. In these patients, there is a strong association with other abnormalities of the chest wall, genitourinary tract, and heart disease. This group of patients needs careful evaluation by many specialists.
+A rare but important group of scoliosis is that in which the muscle is abnormal. Muscular dystrophy is the commonest example. The abnormal muscle does not retain the normal alignment of the vertebral column, and curvature develops as a result. A muscle biopsy is needed to make the diagnosis.
+Other disorders that can produce scoliosis include bone tumors, spinal cord tumors, and localized disc protrusions.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+B
+
+
+Fig. 2.27  Severe scoliosis. A. Radiograph, anteroposterior view. B. Volume-rendered CT, anterior view.
+
+
+
+
+
+
+
+
+
+
+74
+Regional Anatomy  •  Skeletal Framework	2
+
+
+In the clinic
+
+Kyphosis
+Kyphosis is abnormal curvature of the vertebral column in the thoracic region, producing a “hunchback” deformity. This condition occurs in certain disease states, the most dramatic of which is usually secondary to tuberculosis infection of a thoracic vertebral body, where the kyphosis becomes angulated at the site of the lesion. This produces the gibbus deformity, a deformity that was prevalent before the use of antituberculous medication (Fig. 2.28).
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.28  Sagittal CT showing kyphosis.
+
+
+
+
+
+In the clinic
+
+Lordosis
+Lordosis is abnormal curvature of the vertebral column in the lumbar region, producing a swayback deformity.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+75
+Back
+
+
+
+In the clinic
+
+Variation in vertebral numbers
+There are usually seven cervical vertebrae, although in certain diseases these may be fused. Fusion of cervical vertebrae (Fig. 2.29A) can be associated with
+other abnormalities, for example Klippel-Feil syndrome, in which there is fusion of vertebrae CI and CII or CV and CVI, and may be associated with a high-riding scapula (Sprengel’s shoulder) and cardiac abnormalities.
+Variations in the number of thoracic vertebrae also are well described.
+
+
+
+One of the commonest abnormalities in the lumbar vertebrae is a partial fusion of vertebra LV with the sacrum (sacralization of the lumbar vertebra). Partial separation of vertebra SI from the sacrum (lumbarization of first sacral vertebra) may also occur (Fig. 2.29B). The LV vertebra can usually be identified by the iliolumbar ligament, which is a band of connective tissue that runs from the tip of the transverse process of LV to the iliac crest bilaterally
+(Fig. 2.29C).
+A hemivertebra occurs when a vertebra develops only on one side (Fig. 2.29B).
+
+
+Hemivertebra
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A
+
+Fused bodies of cervical vertebrae
+Iliolumbar ligament
+
+
+B
+
+Partial lumbarization of first sacral vertebra
+
+
+
+
+
+C
+
+Fig. 2.29  Variations in vertebral number. A. Fused vertebral bodies of cervical vertebrae. B. Hemivertebra. C. Axial slice MRI through the LV vertebra. The iliolumbar ligament runs from the tip of the LV vertebra transverse process to the iliac crest.
+
+
+
+
+
+
+76
+Regional Anatomy  •  Skeletal Framework	2
+
+
+
+In the clinic
+
+The vertebrae and cancer
+The vertebrae are common sites for metastatic disease (secondary spread of cancer cells). When cancer cells grow within the vertebral bodies and the posterior elements, they interrupt normal bone cell turnover, leading to either bone destruction or formation and destroying the mechanical properties of the bone. A minor injury may therefore lead to vertebral collapse (Fig. 2.30A). Cancer cells have a much
+
+
+
+higher glucose metabolism compared with normal adjacent bone cells. These metastatic cancer cells can therefore be detected by administering radioisotope-labeled glucose to a patient and then tracing where the labeled glucose has been metabolized (Fig. 2.30B). Importantly, vertebrae that contain extensive metastatic disease may extrude fragments of tumor into the vertebral canal, compressing nerves and the spinal cord.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+B1
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A	B2
+
+Fig. 2.30  A. MRI of a spine with multiple collapsed vertebrae due to diffuse metastatic myeloma infiltration. B1, B2. Positron emission tomography CT (PETCT) study detecting cancer cells in the spine that have high glucose metabolism.
+
+
+
+
+
+
+
+
+
+
+
+77
+Back
+
+
+
+In the clinic
+
+Osteoporosis
+Osteoporosis is a pathophysiologic condition in which bone quality is normal but the quantity of bone is deficient. It is a metabolic bone disorder that commonly occurs in women in their 50s and 60s and in men in their 70s.
+Many factors influence the development of osteoporosis, including genetic predetermination, level of activity and nutritional status, and, in particular, estrogen levels in women.
+Typical complications of osteoporosis include “crush” vertebral body fractures, distal fractures of the radius, and hip fractures.
+
+
+
+With increasing age and poor-quality bone, patients are more susceptible to fracture. Healing tends to be impaired in these elderly patients, who consequently require long hospital stays and prolonged rehabilitation.
+Patients likely to develop osteoporosis can be identified by dual-photon X-ray absorptiometry (DXA) scanning.
+Low-dose X-rays are passed through the bone, and by counting the number of photons detected and knowing the dose given, the number of X-rays absorbed by the bone can be calculated. The amount of X-ray absorption can be directly correlated with the bone mass, and this can be used to predict whether a patient is at risk for osteoporotic fractures.
+
+
+
+
+
+
+JOINTS	Anulus fibrosus	Nucleus pulposus Joints between vertebrae in the back
+The two major types of joints between vertebrae are:
+
+■     symphyses between vertebral bodies (Fig. 2.31), and
+■     synovial joints between articular processes (Fig. 2.32).
+
+
+A typical vertebra has a total of six joints with adjacent vertebrae: four synovial joints (two above and two below) and  two  symphyses  (one  above  and  one  below).  Each symphysis includes an intervertebral disc.
+Although the movement between any two vertebrae is
+limited, the summation of movement among all vertebrae	Fig. 2.31  Intervertebral joints. results in a large range of  movement by the vertebral
+column.
+Movements by the vertebral column include flexion, extension, lateral flexion, rotation, and circumduction.
+Movements by vertebrae in a specific region (cervical, thoracic, and lumbar) are determined by the shape and orientation of joint surfaces on the articular processes and on the vertebral bodies.
+
+Layer of hyaline cartilage
+
+
+
+
+
+
+
+
+
+
+
+
+
+78
+Regional Anatomy  •  Joints	2
+
+
+
+Cervical
+
+“Sloped from anterior to posterior”
+
+Zygapophysial joint
+
+
+
+Lateral view
+
+
+Symphyses between vertebral bodies (intervertebral discs)
+The symphysis between adjacent vertebral bodies is formed by a layer of hyaline cartilage on each vertebral body and an intervertebral disc, which lies between the layers.
+The intervertebral disc consists of an outer anulus fibrosus, which surrounds a central nucleus pulposus (Fig. 2.31).
+
+
+
+
+Thoracic
+
+“Vertical”
+
+Zygapophysial joint
+
+■     The anulus fibrosus consists of an outer ring of col-lagen  surrounding  a  wider  zone  of   fibrocartilage arranged in a lamellar configuration. This arrangement of fibers limits rotation between vertebrae.
+■     The nucleus pulposus fills the center of the interver-tebral disc, is gelatinous, and absorbs compression forces between vertebrae.
+
+
+
+
+
+Lateral view
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Lateral view
+
+
+
+
+
+
+
+
+Lumbar
+
+“Wrapped”
+
+
+
+
+
+
+
+Zygapophysial joint
+
+Degenerative changes in the anulus fibrosus can lead to herniation of the nucleus pulposus. Posterolateral hernia-tion can impinge on the roots of  a spinal nerve in the intervertebral foramen.
+
+Joints between vertebral arches (zygapophysial joints)
+The synovial joints between superior and inferior articular processes  on  adjacent  vertebrae  are  the  zygapophysial joints (Fig. 2.32). A thin articular capsule attached to the margins of the articular facets encloses each joint.
+In cervical regions, the zygapophysial joints slope infe-riorly from anterior to posterior and their shape facilitates flexion and extension. In thoracic regions, the joints are oriented vertically and their shape limits flexion and exten-sion, but facilitates rotation. In lumbar regions, the joint surfaces  are  curved  and  adjacent  processes  interlock, thereby limiting range of movement, though flexion and extension are still major movements in the lumbar region.
+
+“Uncovertebral” joints
+The lateral margins of the upper surfaces of typical cervi-cal vertebrae are elevated into crests or lips termed uncinate processes. These may articulate with the body of the ver-tebra above to form small “uncovertebral” synovial joints (Fig. 2.33).
+
+
+Superior view
+
+Fig. 2.32  Zygapophysial joints.
+
+
+
+79
+Back
+
+
+
+
+
+
+
+CIV
+
+
+
+CV
+
+
+
+Uncovertebral joint
+
+Uncinate process
+
+In the clinic
+
+Back pain
+Back pain is an extremely common disorder. It can be related to mechanical problems or to disc protrusion impinging on a nerve. In cases involving discs, it may be necessary to operate and remove the disc that is pressing on the nerve.
+Not infrequently, patients complain of pain and no immediate cause is found; the pain is therefore attributed to mechanical discomfort, which may be caused by degenerative disease. One of the treatments is to pass a needle into the facet joint and inject it with local anesthetic and corticosteroid.
+
+
+
+
+
+Fig. 2.33  Uncovertebral joint.
+
+
+
+
+In the clinic
+
+Herniation of intervertebral discs
+The discs between the vertebrae are made up of a central portion (the nucleus pulposus) and a complex series of fibrous rings (anulus fibrosus). A tear can occur within
+the anulus fibrosus through which the material of the nucleus pulposus can track. After a period of time, this material may track into the vertebral canal or into the intervertebral foramen to impinge on neural structures
+
+
+
+(Fig. 2.34). This is a common cause of back pain. A disc may protrude posteriorly to directly impinge on the cord or the roots of the lumbar nerves, depending on the level, or may protrude posterolaterally adjacent to the pedicle and impinge on the descending root.
+In cervical regions of the vertebral column, cervical disc protrusions often become ossified and are termed disc osteophyte bars.
+
+
+
+
+
+Vertebral canal containing CSF
+and cauda equina	Psoas
+
+Meningeal sac containing CSF and cauda equina
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A
+
+LIV vertebra
+
+
+B
+
+Disc protrusion	Disc protrusion	Facet
+
+
+Fig. 2.34  Disc protrusion. T2-weighted magnetic resonance images of the lumbar region of the vertebral column. A. Sagittal plane. B. Axial plane.
+80
+Regional Anatomy  •  Ligaments	2
+
+
+In the clinic	Posterior longitudinal ligament
+
+Joint diseases
+Some diseases have a predilection for synovial joints rather than symphyses. A typical example is rheumatoid arthritis, which primarily affects synovial joints and synovial bursae, resulting in destruction of the joint and its lining. Symphyses are usually preserved.
+
+
+
+
+
+
+
+LIGAMENTS
+
+Joints between vertebrae are reinforced and supported by numerous ligaments, which pass between vertebral bodies and interconnect components of the vertebral arches.
+
+
+
+Anterior and posterior longitudinal ligaments
+
+The anterior and posterior longitudinal ligaments are on the anterior and posterior surfaces of the vertebral bodies and extend along most of the vertebral column (Fig. 2.35). The  anterior  longitudinal  ligament  is  attached superiorly to the base of the skull and extends inferiorly to attach to the anterior surface of  the sacrum. Along its length it is attached to the vertebral bodies and interverte-
+bral discs.
+The posterior longitudinal ligament is on the poste-rior surfaces of the vertebral bodies and lines the anterior surface of the vertebral canal. Like the anterior longitudi-nal ligament, it is attached along its length to the vertebral bodies and intervertebral discs. The upper part of the pos-terior longitudinal ligament that connects CII to the intra-cranial aspect of the base of the skull is termed the tectorial membrane (see Fig. 2.20B).
+
+Ligamenta flava
+The ligamenta  flava, on each side, pass between the laminae  of  adjacent  vertebrae  (Fig.  2.36). These  thin, broad ligaments consist predominantly of  elastic tissue and form part of  the posterior surface of  the vertebral
+
+
+
+
+
+
+
+
+
+Anterior longitudinal ligament
+
+Fig. 2.35  Anterior and posterior longitudinal ligaments of vertebral column.
+
+
+
+canal. Each ligamentum flavum runs between the posterior surface of the lamina on the vertebra below to the anterior surface of the lamina of the vertebra above. The ligamenta flava resist separation of the laminae in flexion and assist in extension back to the anatomical position.
+
+
+Supraspinous ligament and ligamentum nuchae
+
+The  supraspinous  ligament  connects  and  passes  along the tips of the vertebral spinous processes from vertebra
+
+
+
+
+
+
+
+81
+Back
+
+
+Superior	Superior
+
+Ligamenta flava
+
+Ligamenta flava
+
+
+
+
+
+
+
+
+Posterior
+
+
+
+
+
+
+
+Inferior	Inferior	Vertebral canal
+
+Fig. 2.36  Ligamenta flava.
+
+
+
+
+CVII to the sacrum (Fig. 2.37). From vertebra CVII to the  skull,  the  ligament  becomes  structurally  distinct from more caudal parts of the ligament and is called the ligamentum nuchae.
+The ligamentum nuchae is a triangular, sheet-like structure in the median sagittal plane:
+
+
+
+External occipital protuberance
+
+
+
+Ligamentum nuchae
+
+
+
+■     The base of the triangle is attached to the skull, from the external occipital protuberance to the foramen magnum.
+■     The apex is attached to the tip of the spinous process of vertebra CVII.
+■     The deep side of the triangle is attached to the posterior tubercle of vertebra CI and the spinous processes of the other cervical vertebrae.
+
+
+Spinous process of vertebra CVII
+
+
+The ligamentum nuchae supports the head. It resists	Supraspinous ligament flexion and facilitates returning the head to the anatomi-
+cal position. The broad lateral surfaces and the posterior edge  of  the  ligament  provide  attachment  for  adjacent muscles.
+
+
+
+Interspinous ligaments
+Interspinous ligaments pass between adjacent vertebral spinous processes (Fig. 2.38). They attach from the base to the apex of each spinous process and blend with the supra-spinous  ligament  posteriorly  and  the  ligamenta  flava
+82	anteriorly on each side.
+
+
+
+
+
+
+
+Fig. 2.37  Supraspinous ligament and ligamentum nuchae.
+Regional Anatomy  •  Ligaments	2
+
+
+In the clinic
+
+Ligamenta flava
+The ligamenta flava are important structures associated with the vertebral canal (Fig. 2.39). In degenerative conditions of the vertebral column, the ligamenta flava may hypertrophy. This is often associated with hypertrophy and arthritic change of the zygapophysial joints. In combination, zygapophysial joint hypertrophy, ligamenta flava hypertrophy, and a mild disc protrusion can reduce the dimensions of the vertebral canal,
+Ligamentum flavum	producing the syndrome of spinal stenosis.
+
+Supraspinous ligament
+
+Interspinous ligament
+
+
+
+
+
+
+Ligamentum flavum
+
+
+
+
+
+Fig. 2.39  Axial slice MRI through the lumbar spine demonstrating bilateral hypertrophy of the ligamentum flavum.
+Ligamentum flavum	Supraspinous ligament
+
+Fig. 2.38  Interspinous ligaments.
+
+
+
+
+In the clinic
+
+Vertebral fractures
+Vertebral fractures can occur anywhere along the vertebral column. In most instances, the fracture will heal under appropriate circumstances. At the time of injury, it is not the fracture itself but related damage to the contents of the vertebral canal and the surrounding tissues that determines the severity of the patient’s condition.
+Vertebral column stability is divided into three arbitrary clinical “columns”: the anterior column consists of the vertebral bodies and the anterior longitudinal ligament; the middle column comprises the vertebral body and the posterior longitudinal ligament; and the posterior column is made up of the ligamenta flava, interspinous ligaments, supraspinous ligaments, and the ligamentum nuchae in the cervical vertebral column.
+Destruction of one of the clinical columns is usually a stable injury requiring little more than rest and appropriate
+
+
+
+analgesia. Disruption of two columns is highly likely to be unstable and requires fixation and immobilization. A
+three-column spinal injury usually results in a significant neurological event and requires fixation to prevent further extension of the neurological defect and to create vertebral column stability.
+At the craniocervical junction, a complex series of ligaments create stability. If the traumatic incident disrupts craniocervical stability, the chances of a significant spinal cord injury are extremely high. The consequences are quadriplegia. In addition, respiratory function may be compromised by paralysis of the phrenic nerve (which arises from spinal nerves C3 to C5), and severe hypotension (low blood pressure) may result from central disruption of the sympathetic part of the autonomic division of the nervous system.
+(continues)	83
+Back
+
+
+
+In the clinic—cont’d
+
+Mid and lower cervical vertebral column disruption may produce a range of complex neurological problems involving the upper and lower limbs, although below the level of C5, respiratory function is unlikely to be compromised.
+Lumbar vertebral column injuries are rare. When they occur, they usually involve significant force. Knowing that a significant force is required to fracture a vertebra, one must assess the abdominal organs and the rest of the axial skeleton for further fractures and visceral rupture.
+Vertebral injuries may also involve the soft tissues and supporting structures between the vertebrae. Typical examples of this are the unifacetal and bifacetal cervical vertebral dislocations that occur in hyperflexion injuries.
+Pars interarticularis fractures
+The pars interarticularis is a clinical term to describe the specific region of a vertebra between the superior and
+
+
+
+inferior facet (zygapophysial) joints (Fig. 2.40A). This region is susceptible to trauma, especially in athletes.
+If a fracture occurs around the pars interarticularis, the vertebral body may slip anteriorly and compress the vertebral canal.
+The most common sites for pars interarticularis fractures are the LIV and LV levels (Fig. 2.40B,C). (Clinicians often refer to parts of the back in shorthand terms that are not strictly anatomical; for example, facet joints and apophyseal joints are terms used instead of zygapophysial joints, and spinal column is used instead of vertebral column.)
+It is possible for a vertebra to slip anteriorly upon its inferior counterpart without a pars interarticularis fracture. Usually this is related to abnormal anatomy of the facet joints, facet joint degenerative change. This disorder is termed spondylolisthesis.
+
+
+Superior articular process
+Pars fracture
+
+
+
+
+
+
+
+
+
+
+
+
+B
+
+
+
+
+
+
+
+
+
+Pars interarticularis fracture
+
+
+A
+
+Pedicle	Pars interarticularis	C
+
+Fig. 2.40  Radiograph of lumbar region of vertebral column, oblique view (“Scottie dog”). A. Normal radiograph of lumbar region of vertebral column, oblique view. In this view, the transverse process (nose), pedicle (eye), superior articular process (ear), inferior articular process (front leg), and pars interarticularis (neck) resemble a dog. A fracture of the pars interarticularis is visible as a break in the neck of the dog, or the appearance of a collar. B. Fracture of pars interarticularis. C. CT of lumbar spine shows fracture of the LV pars interarticularis.
+84
+Regional Anatomy  •  Ligaments	2
+
+
+
+In the clinic
+
+Surgical procedures on the back Discectomy/laminectomy
+A prolapsed intervertebral disc may impinge upon the meningeal (thecal) sac, cord, and most commonly the nerve root, producing symptoms attributable to that level. In some instances the disc protrusion will undergo a degree of involution that may allow symptoms to resolve without intervention. In some instances pain, loss of function, and failure to resolve may require surgery to remove the disc protrusion.
+It is of the utmost importance that the level of the disc protrusion is identified before surgery. This may require MRI scanning and on-table fluoroscopy to prevent operating on the wrong level. A midline approach to the right or to the left of the spinous processes will depend upon the most prominent site of the disc bulge. In some instances removal of the lamina will increase the potential space and may relieve symptoms. Some surgeons perform a small fenestration (windowing) within the ligamentum flavum. This provides access to the canal. The meningeal sac and its
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A
+
+
+
+contents are gently retracted, exposing the nerve root and the offending disc. The disc is dissected free, removing its effect on the nerve root and the canal.
+Spinal Fusion
+Spinal fusion is performed when it is necessary to fuse one vertebra with the corresponding superior or inferior vertebra, and in some instances multilevel fusion may be necessary. Indications are varied, though they include stabilization after fracture, stabilization related to tumor infiltration, and stabilization when mechanical pain is produced either from the disc or from the posterior elements.
+There are a number of surgical methods in which a fusion can be performed, through either a posterior approach and fusing the posterior elements, an anterior approach by removal of the disc and either disc replacement or anterior fusion, or in some instances a 360° fusion where the posterior elements and the vertebral bodies are fused
+(Fig. 2.41A,B).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+B
+
+
+Fig. 2.41  A. Anterior lumbar interbody fusion (ALIF). B. Posterior lumbar interbody fusion (PLIF).
+
+
+
+
+
+
+85
+Back
+
+
+
+BACK MUSCULATURE
+
+Muscles of the back are organized into superficial, interme-diate, and deep groups.
+Muscles in the superficial and intermediate groups are extrinsic muscles because they originate embryologically from locations other than the back. They are innervated by anterior rami of spinal nerves:
+
+
+Superficial group of back muscles
+The muscles in the superficial group are immediately deep to the skin and superficial fascia (Figs. 2.42 to 2.45). They attach  the  superior  part  of  the  appendicular  skeleton (clavicle,  scapula,  and  humerus)  to  the  axial  skeleton (skull, ribs, and vertebral column). Because these muscles are primarily involved with movements of this part of the
+
+
+
+
+■     The superficial group consists of muscles related to and involved in movements of the upper limb.
+■     The intermediate group consists of muscles attached to the ribs and may serve a respiratory function.
+
+Muscles of the deep group are intrinsic muscles because
+
+appendicular skeleton, they are sometimes referred to as the appendicular group.
+Muscles in the superficial group include the trapezius, latissimus dorsi, rhomboid major, rhomboid minor, and levator scapulae. The rhomboid major, rhomboid minor, and levator scapulae muscles are located deep to the trape-zius muscle in the superior part of the back.
+
+they develop in the back. They are innervated by posterior rami of spinal nerves and are directly related to movements of the vertebral column and head.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+86
+Regional Anatomy  •  Back Musculature	2
+
+
+
+
+
+
+
+
+
+Greater occipital nerve (posterior ramus of C2)
+
+Spinous process of CVII
+Third occipital nerve (posterior ramus of C3)
+
+Medial branches of posterior rami
+
+Acromion	Trapezius
+
+
+
+Spine of scapula
+
+
+
+
+
+
+
+
+
+
+Latissimus dorsi
+
+
+
+Lateral branches of posterior rami
+Iliac crest
+
+
+
+Thoracolumbar fascia
+
+
+
+
+
+
+
+
+Fig. 2.42  Superficial group of back muscles—trapezius and latissimus dorsi.
+
+
+
+
+
+
+87
+Back
+
+
+
+
+
+
+
+
+
+
+
+Ligamentum nuchae
+
+
+
+Trapezius	Levator scapulae
+
+
+Rhomboid minor
+
+
+
+
+
+
+Rhomboid major
+
+
+
+
+
+
+
+Latissimus dorsi
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.43  Superficial group of back muscles—trapezius and latissimus dorsi, with rhomboid major, rhomboid minor, and levator scapulae located deep to trapezius in the superior part of the back.
+
+88
+Regional Anatomy  •  Back Musculature	2
+
+
+
+
+Trapezius
+Each trapezius muscle is flat and triangular, with the base of  the triangle situated along the vertebral column (the muscle’s origin) and the apex pointing toward the tip of the shoulder (the muscle’s insertion) (Fig. 2.43 and Table 2.1). The muscles on both sides together form a trapezoid.
+The superior fibers of the trapezius, from the skull and upper portion of the vertebral column, descend to attach to the lateral third of  the clavicle and to the acromion
+
+together to rotate the lateral aspect of the scapula upward, which needs to occur when raising the upper limb above the head.
+Motor innervation of the trapezius is by the accessory nerve [XI], which descends from the neck onto the deep surface of the muscle (Fig. 2.44). Proprioceptive fibers from the trapezius pass in the branches of the cervical plexus and enter the spinal cord at spinal cord levels C3 and C4.
+The blood supply to the trapezius is from the superficial branch  of  the  transverse  cervical  artery,  the  acromial
+
+of  the scapula. Contraction of  these fibers elevates the	branch  of   the  suprascapular  artery,  and  the  dorsal scapula. In addition, the superior and inferior fibers work	branches of posterior intercostal arteries.
+
+
+
+
+
+
+
+
+
+
+
+Levator scapulae
+
+
+Trapezius	Superficial branch of transverse cervical artery
+
+
+Accessory nerve [XI]
+
+
+
+Rhomboid minor
+
+
+Rhomboid major
+
+
+
+
+
+Latissimus dorsi
+
+
+
+
+
+
+
+
+
+Fig. 2.44  Innervation and blood supply of trapezius.
+
+
+
+89
+Back
+
+
+
+
+
+
+
+
+
+
+
+/LJDPHQWXPQXFKDH
+
+
+
+
+/HYDWRUVFDSXODH	7UDSH]LXV
+
+
+
+
+5KRPERLGPLQRU
+
+
+
+5KRPERLGPDMRU
+
+
+
+
+
+/DWLVVLPXVGRUVL
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.45  Rhomboid muscles and levator scapulae.
+
+
+90
+Regional Anatomy  •  Back Musculature	2
+
+
+Table 2.1    Superficial (appendicular) group of back muscles
+
+
+Muscle Trapezius
+
+
+
+
+Latissimus dorsi
+
+
+Levator scapulae
+
+Rhomboid major
+
+
+Rhomboid minor
+
+Origin
+Superior nuchal line, external occipital protuberance, ligamentum nuchae, spinous processes of CVII to TXII
+
+
+Spinous processes of TVII to LV and sacrum, iliac crest, ribs X to XII
+Transverse processes of CI to CIV
+Spinous processes of TII to TV
+
+
+Lower portion of ligamentum nuchae, spinous processes of CVII and TI
+
+Insertion
+Lateral one third of clavicle, acromion, spine of scapula
+
+
+
+Floor of intertubercular sulcus of humerus
+
+Upper portion medial border of scapula
+Medial border of scapula between spine and inferior angle
+Medial border of scapula at spine of scapula
+
+Innervation
+Motor—accessory nerve [XI]; proprioception—C3 and C4
+
+
+
+Thoracodorsal nerve (C6 to C8)
+
+C3 to C4 and dorsal scapular nerve (C4, C5)
+Dorsal scapular nerve (C4, C5)
+
+Dorsal scapular nerve (C4, C5)
+
+Function
+Assists in rotating the scapula during abduction of humerus above horizontal; upper fibers elevate, middle fibers adduct, and lower fibers depress scapula
+Extends, adducts, and medially rotates humerus
+
+Elevates scapula
+
+Retracts (adducts) and elevates scapula
+
+Retracts (adducts) and elevates scapula
+
+
+
+
+
+
+
+
+Latissimus dorsi
+Latissimus dorsi is a large, flat triangular muscle that begins in the lower portion of  the back and tapers as it ascends to a narrow tendon that attaches to the humerus anteriorly (Figs. 2.42 to 2.45 and Table 2.1). As a result, movements associated with this muscle include extension, adduction, and medial rotation of  the upper limb. The latissimus dorsi can also depress the shoulder, preventing its upward movement.
+The thoracodorsal nerve of the brachial plexus inner-vates the latissimus dorsi muscle. Associated with this nerve is the thoracodorsal artery, which is the primary blood supply of the muscle. Additional small arteries come from dorsal branches of posterior intercostal and lumbar arteries.
+
+Levator scapulae
+Levator scapulae is a slender muscle that descends from the transverse processes of the upper cervical vertebrae to the upper portion of the scapula on its medial border at the superior angle (Figs. 2.43 and 2.45 and Table 2.1). It
+
+elevates the scapula and may assist other muscles in rotat-ing the lateral aspect of the scapula inferiorly.
+The levator scapulae is innervated by branches from the anterior rami of spinal nerves C3 and C4 and the dorsal scapular nerve, and its arterial supply consists of branches primarily  from  the  transverse  and  ascending  cervical arteries.
+
+Rhomboid minor and rhomboid major
+The two rhomboid muscles are inferior to levator scapulae (Fig. 2.45 and Table 2.1). Rhomboid minor is superior to rhomboid major, and is a small, cylindrical muscle that arises from the ligamentum nuchae of the neck and the spinous processes of vertebrae CVII and TI and attaches to the medial scapular border opposite the root of the spine of the scapula.
+The  larger  rhomboid  major  originates  from  the spinous processes of  the upper thoracic vertebrae and attaches to the medial scapular border inferior to rhomboid minor.
+The two rhomboid muscles work together to retract or pull the scapula toward the vertebral column. With other
+
+
+
+
+
+
+
+
+
+91
+Back
+
+
+
+muscles they may also rotate the lateral aspect of  the scapula inferiorly.
+The dorsal scapular nerve, a branch of  the brachial plexus, innervates both rhomboid muscles (Fig. 2.46).
+
+Intermediate group of back muscles
+The muscles in the intermediate group of  back muscles consist of  two thin muscular sheets in the superior and inferior  regions  of  the  back,  immediately  deep  to  the muscles in the superficial group (Fig. 2.47 and Table 2.2). Fibers from these two serratus posterior muscles (serratus posterior superior and serratus posterior inferior) pass obliquely outward from the vertebral column to attach to the ribs. This positioning suggests a respiratory function,
+
+and at times, these muscles have been referred to as the respiratory group.
+Serratus  posterior  superior  is  deep  to  the  rhomboid muscles,  whereas  serratus  posterior  inferior  is  deep  to the latissimus dorsi. Both serratus posterior muscles are attached to the vertebral column and associated structures medially, and either descend (the fibers of  the serratus posterior superior) or ascend (the fibers of  the serratus posterior inferior) to attach to the ribs. These two muscles therefore elevate and depress the ribs.
+The serratus posterior muscles are innervated by seg-mental branches of  anterior rami of  intercostal nerves. Their vascular supply is provided by a similar segmental pattern through the intercostal arteries.
+
+
+
+
+
+
+
+
+
+Levator scapulae
+
+Dorsal scapular nerve
+
+Superficial branch of transverse cervical artery
+
+Trapezius
+
+
+
+
+Rhomboid minor
+
+
+
+Rhomboid major
+
+
+Deep branch of transverse cervical artery
+
+
+
+Latissimus dorsi
+
+
+
+
+Fig. 2.46  Innervation and blood supply of the rhomboid muscles.
+
+
+
+
+
+
+92
+Regional Anatomy  •  Back Musculature	2
+
+
+
+
+
+
+
+
+
+
+
+
+
+Levator scapulae	Serratus posterior superior
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Serratus posterior inferior
+
+
+Posterior layer of thoracolumbar fascia
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.47  Intermediate group of back muscles—serratus posterior muscles.
+
+
+
+Table 2.2    Intermediate (respiratory) group of back muscles
+
+
+Muscle
+Serratus posterior superior
+
+
+Serratus posterior inferior
+
+Origin
+Lower portion of ligamentum nuchae, spinous processes of CVII to TIII, and supraspinous ligaments
+Spinous processes of TXI to LIII and supraspinous ligaments
+
+Insertion
+Upper border of ribs II to V just lateral to their angles
+
+Lower border of ribs IX to XII just lateral to their angles
+
+Innervation
+Anterior rami of upper thoracic nerves (T2 to T5)
+
+Anterior rami of lower thoracic nerves (T9 to T12)
+
+Function
+Elevates ribs II to V
+
+
+
+Depresses ribs IX to XII and may prevent lower ribs from being elevated when the
+diaphragm contracts	93
+Back
+
+
+
+Deep group of back muscles	Psoas major muscle
+The deep or intrinsic muscles of  the back extend from the pelvis to the skull and are innervated by segmental branches  of  the  posterior  rami  of  spinal  nerves. They include:
+
+Transversus abdominis muscle
+
+Quadratus lumborum muscle
+
+
+
+■     the extensors and rotators of  the head and neck— the  splenius  capitis  and  cervicis  (spinotransversales muscles),
+■     the extensors and rotators of the vertebral column—the erector spinae and transversospinales, and
+■     the  short  segmental  muscles—the  interspinales  and	Erector spinae muscles intertransversarii.
+
+The  vascular  supply  to  this  deep  group  of  muscles
+
+
+
+
+
+Latissimus dorsi muscle
+Thoracolumbar fascia Anterior layer
+Middle layer
+Posterior layer
+
+
+
+is through branches of the vertebral, deep cervical, occipi-tal, transverse cervical, posterior intercostal, subcostal, lumbar, and lateral sacral arteries.
+
+Thoracolumbar fascia
+The thoracolumbar fascia covers the deep muscles of the back and trunk (Fig. 2.48). This fascial layer is critical to the overall organization and integrity of the region:
+
+
+Fig. 2.48  Thoracolumbar fascia and the deep back muscles (transverse section).
+
+
+abdominal wall) and is attached medially to the trans-verse processes of the lumbar vertebrae—inferiorly, it is attached to the iliac crest and, superiorly, it forms the  lateral  arcuate  ligament  for  attachment  of  the diaphragm.
+
+
+
+■     Superiorly, it passes anteriorly to the serratus posterior muscle and is continuous with deep fascia in the neck.
+■     In the thoracic region, it covers the deep muscles and separates them from the muscles in the superficial and intermediate groups.
+■     Medially, it attaches to the spinous processes of  the thoracic vertebrae and, laterally, to the angles of the ribs.
+
+The medial attachments of  the latissimus dorsi and
+
+
+The posterior and middle layers of the thoracolumbar fascia come together at the lateral margin of the erector spinae (Fig. 2.48). At the lateral border of the quadratus lumborum, the anterior layer joins them and forms the aponeurotic origin for the transversus abdominis muscle of the abdominal wall.
+
+Spinotransversales muscles
+
+
+
+serratus posterior inferior muscles blend into the thoraco-lumbar fascia. In the lumbar region, the thoracolumbar fascia consists of three layers:
+
+The two spinotransversales muscles run from the spinous processes and ligamentum nuchae upward and laterally (Fig. 2.49 and Table 2.3):
+
+
+
+■     The posterior layer is thick and is attached to the spinous processes of the lumbar vertebrae and sacral vertebrae and to the supraspinous ligament—from these attach-ments, it extends laterally to cover the erector spinae.
+■     The middle layer is attached medially to the tips of the transverse processes of the lumbar vertebrae and inter-transverse ligaments—inferiorly, it is attached to the
+
+■     The splenius capitis is a broad muscle attached to the occipital bone and mastoid process of  the temporal bone.
+■     The splenius cervicis is a narrow muscle attached to the transverse processes of the upper cervical vertebrae.
+
+Together the spinotransversales muscles draw the head
+
+iliac crest and, superiorly, to the lower border of rib XII. ■     The anterior layer covers the anterior surface of  the
+quadratus lumborum muscle (a muscle of the posterior
+
+backward, extending the neck. Individually, each muscle rotates the head to one side—the same side as the contract-ing muscle.
+
+
+
+
+94
+Regional Anatomy  •  Back Musculature	2
+
+
+
+
+
+
+
+
+
+
+
+Ligamentum nuchae
+
+Splenius capitis
+
+
+Levator scapulae
+
+
+
+
+
+Splenius cervicis
+
+
+
+
+
+
+
+
+
+
+Fig. 2.49  Deep group of back muscles—spinotransversales muscles (splenius capitis and splenius cervicis).
+
+
+
+
+Table 2.3
+
+Muscle
+
+Spinotransversales muscles
+
+Origin	Insertion	Innervation	Function
+
+
+
+Splenius capitis
+
+
+
+
+Splenius cervicis
+
+Lower half of ligamentum nuchae, spinous processes of CVII to TIV
+
+
+Spinous processes of TIII to TVI
+
+Mastoid process, skull below lateral one third of superior nuchal line
+
+
+Transverse processes of CI to CIII
+
+Posterior rami of middle cervical nerves
+
+
+
+Posterior rami of lower cervical nerves
+
+Together—draw head backward, extending neck; individually—draw and rotate head to one side (turn face to same side)
+Together—extend neck; individually—draw and rotate head to one side (turn face to same side)
+
+
+
+
+
+Erector spinae muscles
+The erector spinae is the largest group of  intrinsic back muscles. The muscles lie posterolaterally to the vertebral column  between  the  spinous  processes  medially  and the angles of  the ribs laterally. They are covered in the thoracic and lumbar regions by thoracolumbar fascia and the  serratus  posterior  inferior,  rhomboid,  and  splenius muscles.  The  mass  arises  from  a  broad,  thick  tendon
+
+
+
+attached  to  the  sacrum,  the  spinous  processes  of  the lumbar and lower thoracic vertebrae, and the iliac crest (Fig. 2.50 and Table 2.4). It divides in the upper lumbar region  into  three  vertical  columns  of  muscle,  each  of which is further subdivided regionally (lumborum, thora-cis, cervicis, and capitis), depending on where the muscles
+attach superiorly.	95
+Back
+
+
+
+
+
+
+
+
+
+
+
+Ligamentum nuchae
+
+Splenius capitis
+
+Longissimus capitis
+
+
+
+Spinous process of CVII	Iliocostalis cervicis
+
+Longissimus cervicis
+
+
+
+
+
+Spinalis
+
+Longissimus
+
+Spinalis thoracis
+
+
+Longissimus thoracis
+
+
+Iliocostalis thoracis Iliocostalis
+
+
+
+
+
+Iliocostalis lumborum
+
+
+
+
+Iliac crest
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.50  Deep group of back muscles—erector spinae muscles.
+
+96
+Regional Anatomy  •  Back Musculature	2
+
+
+
+Table 2.4
+
+Muscle
+
+Erector spinae group of back muscles
+
+Origin	Insertion
+
+
+
+Iliocostalis lumborum
+
+
+Iliocostalis thoracis
+
+Iliocostalis cervicis Longissimus thoracis
+
+Longissimus cervicis
+
+Longissimus capitis
+
+
+Spinalis thoracis Spinalis cervicis
+
+Spinalis capitis
+
+Sacrum, spinous processes of lumbar and lower two thoracic vertebrae and their supraspinous ligaments, and the iliac crest
+Angles of the lower six ribs
+
+Angles of ribs III to VI
+Blends with iliocostalis in lumbar region and is attached to transverse processes of lumbar vertebrae
+Transverse processes of upper four or five thoracic vertebrae
+Transverse processes of upper four or five thoracic vertebrae and articular processes of lower three or four cervical vertebrae
+Spinous processes of TX or TXI to LII
+Lower part of ligamentum nuchae and spinous process of CVII (sometimes TI to TII)
+Usually blends with semispinalis capitis
+
+Angles of the lower six or seven ribs
+
+
+Angles of the upper six ribs and the transverse process of CVII
+Transverse processes of CIV to CVI
+Transverse processes of all thoracic vertebrae and just lateral to the tubercles of the lower nine or ten ribs
+Transverse processes of CII to CVI
+
+Posterior margin of the mastoid process
+
+
+Spinous processes of TI to TVIII (varies) Spinous process of CII (axis)
+
+With semispinalis capitis
+
+
+
+
+■     The outer or most laterally placed column of the erector spinae muscles is the iliocostalis, which is associated with the costal elements and passes from the common tendon of origin to multiple insertions into the angles of  the ribs and the transverse processes of  the lower cervical vertebrae.
+■     The middle or intermediate column is the longissimus, which is the largest of  the erector spinae subdivision
+
+Transversospinales muscles
+The transversospinales muscles run obliquely upward and medially from transverse processes to spinous processes, filling the groove between these two vertebral projections (Fig. 2.51 and Table 2.5). They are deep to the erector spinae and consist of three major subgroups—the semispi-nalis, multifidus, and rotatores muscles.
+
+
+
+extending from the common tendon of  origin to the base of  the skull. Throughout this vast expanse, the lateral  positioning  of  the  longissimus  muscle  is  in the  area  of  the  transverse  processes  of  the  various vertebrae.
+■     The most medial muscle column is the spinalis, which is the smallest of the subdivisions and interconnects the spinous processes of adjacent vertebrae. The spinalis is most constant in the thoracic region and is generally absent in the cervical region. It is associated with a deeper muscle (the semispinalis capitis) as the erector spinae group approaches the skull.
+
+The muscles in the erector spinae group are the primary
+
+
+■     The semispinalis muscles are the most superficial col-lection of muscle fibers in the transversospinales group. These muscles begin in the lower thoracic region and end by attaching to the skull, crossing between four and six vertebrae from their point of origin to point of attachment.  Semispinalis  muscles  are  found  in  the thoracic and cervical regions, and attach to the occipital bone at the base of the skull.
+■     Deep to the semispinalis is the second group of muscles, the multifidus. Muscles in this group span the length of the vertebral column, passing from a lateral point of origin upward and medially to attach to spinous proc-esses and spanning between two and four vertebrae. The multifidus muscles are present throughout the length of
+
+
+
+extensors of the vertebral column and head. Acting bilat-erally, they straighten the back, returning it to the upright position from a flexed position, and pull the head posteriorly. They  also  participate  in  controlling  vertebral  column flexion  by  contracting  and  relaxing  in  a  coordinated fashion.  Acting  unilaterally,  they  bend  the  vertebral column laterally. In addition, unilateral contractions of muscles attached to the head turn the head to the actively contracting side.
+
+the  vertebral  column  but  are  best  developed  in  the lumbar region.
+■     The small rotatores muscles are the deepest of  the transversospinales group. They are present throughout the length of the vertebral column but are best devel-oped in the thoracic region. Their fibers pass upward and  medially  from  transverse  processes  to  spinous processes  crossing  two  vertebrae  (long  rotators)  or
+attaching to an adjacent vertebra (short rotators).	97
+Back
+
+
+
+
+
+
+
+
+Rectus capitis posterior minor
+
+
+Obliquus capitis superior
+
+
+Rectus capitis posterior major Semispinalis capitis	Obliquus capitis inferior
+
+
+Spinous process of CVII
+
+
+
+
+
+Semispinalis thoracis
+Rotatores thoracis (short, long)
+
+
+
+Levatores costarum (short, long)
+
+
+
+
+Multifidus
+
+
+
+
+Intertransversarius
+
+
+
+
+Erector spinae
+
+
+
+
+
+
+
+
+
+Fig. 2.51  Deep group of back muscles—transversospinales and segmental muscles.
+
+98
+Regional Anatomy  •  Back Musculature	2
+
+
+
+Table 2.5
+
+Muscle
+
+Transversospinales group of back muscles
+
+Origin	Insertion
+
+
+
+Semispinalis thoracis
+
+Semispinalis cervicis Semispinalis capitis
+
+Multifidus
+
+
+
+Rotatores lumborum Rotatores thoracis
+Rotatores cervicis
+
+Transverse processes of TVI to TX
+
+Transverse processes of upper five or six thoracic vertebrae
+Transverse processes of TI to TVI (or TVII) and CVII and articular processes of CIV to CVI
+Sacrum, origin of erector spinae, posterior superior iliac spine, mammillary processes of lumbar vertebrae, transverse processes of thoracic vertebrae, and articular processes of lower four cervical vertebrae
+Transverse processes of lumbar vertebrae Transverse processes of thoracic vertebrae
+Articular processes of cervical vertebrae
+
+Spinous processes of upper four thoracic and lower two cervical vertebrae
+Spinous processes of CII (axis) to CV
+Medial area between the superior and inferior nuchal lines of occipital bone
+Base of spinous processes of all vertebrae from LV to CII (axis)
+
+
+Spinous processes of lumbar vertebrae Spinous processes of thoracic vertebrae
+Spinous processes of cervical vertebrae
+
+
+
+
+When muscles in the transversospinales group contract bilaterally, they extend the vertebral column, an action similar to that of the erector spinae group. However, when muscles on only one side contract, they pull the spinous processes toward the transverse processes on that side, causing  the  trunk  to  turn  or  rotate  in  the  opposite direction.
+
+processes of vertebrae CVII and TI to TXI. They have an oblique lateral and downward direction and insert into the rib below the vertebra of origin in the area of the tubercle. Contraction elevates the ribs.
+■     The second group of  segmental muscles are the true segmental muscles of  the back—the interspinales, which pass between adjacent spinous processes, and the
+
+One muscle in the transversospinales group, the semi-	intertransversarii,  which  pass  between  adjacent
+
+spinalis capitis, has a unique action because it attaches to the skull. Contracting bilaterally, this muscle pulls the head posteriorly, whereas unilateral contraction pulls the head posteriorly and turns it, causing the chin to move superiorly and turn toward the side of  the contracting muscle. These actions are similar to those of  the upper erector spinae.
+
+Segmental muscles
+The two groups of segmental muscles (Fig. 2.51 and Table 2.6) are deeply placed in the back and innervated by pos-terior rami of spinal nerves.
+
+transverse processes. These postural muscles stabilize adjoining vertebrae during movements of the vertebral column  to  allow  more  effective  action  of  the  large muscle groups.
+
+
+
+Suboccipital muscles
+A small group of deep muscles in the upper cervical region at the base of  the occipital bone move the head. They connect vertebra CI (the atlas) to vertebra CII (the axis) and connect both vertebrae to the base of the skull. Because of their location they are sometimes referred to as suboc-
+
+■     The first group of segmental muscles are the levatores costarum muscles, which arise from the transverse
+
+cipital muscles (Figs. 2.51 and 2.52 and Table 2.7). They include, on each side:
+
+
+
+
+Table 2.6
+
+Muscle
+
+Segmental back muscles
+
+Origin	Insertion	Function
+
+
+
+Levatores costarum
+
+Interspinales
+
+
+
+Intertransversarii
+
+Short paired muscles arising from transverse processes of CVII to TXI
+Short paired muscles attached to the spinous processes of contiguous vertebrae, one on each side of the interspinous ligament
+Small muscles between the transverse processes of contiguous vertebrae
+
+The rib below vertebra of origin near tubercle
+
+Contraction elevates rib
+
+Postural muscles that stabilize adjoining vertebrae during movements of vertebral column
+
+Postural muscles that stabilize adjoining vertebrae during
+movements of vertebral column	99
+Back
+
+
+
+
+Splenius capitis
+
+Semispinalis capitis
+Obliquus capitis superior
+
+
+Vertebral artery
+
+Rectus capitis posterior minor	Posterior ramus of C1
+
+Rectus capitis posterior major
+
+Obliquus capitis inferior
+
+Spinous process of CII
+
+
+Semispinalis cervicis
+
+Semispinalis capitis
+Longissimus capitis
+
+
+Splenius capitis
+
+
+Fig. 2.52  Deep group of back muscles—suboccipital muscles. This also shows the borders of the suboccipital triangle.
+
+
+
+Table 2.7
+
+Muscle
+
+Suboccipital group of back muscles
+
+Origin	Insertion	Innervation	Function
+
+
+
+Rectus capitis posterior major
+
+Rectus capitis posterior minor
+
+Obliquus capitis superior
+
+
+Obliquus capitis inferior
+
+Spinous process of axis (CII)
+
+Posterior tubercle of atlas (CI)
+
+Transverse process of atlas (CI)
+
+Spinous process of axis (CII)
+
+Lateral portion of occipital bone below inferior nuchal line
+Medial portion of occipital bone below inferior nuchal line
+Occipital bone between superior and inferior nuchal lines
+Transverse process of atlas (CI)
+
+Posterior ramus of C1
+
+
+Posterior ramus of C1
+
+
+Posterior ramus of C1
+
+
+Posterior ramus of C1
+
+Extension of head; rotation of face to same side as muscle
+
+Extension of head
+
+
+Extension of head and bends it to same side
+
+Rotation of face to same side
+
+
+
+
+■     rectus capitis posterior major, ■     rectus capitis posterior minor, ■     obliquus capitis inferior, and
+■     obliquus capitis superior.
+
+Contraction of  the suboccipital muscles extends and
+
+
+this area is from branches of the vertebral and occipital arteries.
+The suboccipital muscles form the boundaries of  the suboccipital  triangle,  an  area  that  contains  several important structures (Fig. 2.52):
+
+
+
+rotates the head at the atlanto-occipital and atlanto-axial joints, respectively.
+The suboccipital muscles are innervated by the posterior ramus of  the first cervical nerve, which enters the area between the vertebral artery and the posterior arch of the
+100	atlas (Fig. 2.52). The vascular supply to the muscles in
+
+■     The rectus capitis posterior major muscle forms the medial border of the triangle.
+■     The obliquus capitis superior muscle forms the lateral border.
+■     The obliquus capitis inferior muscle forms the inferior border.
+Regional Anatomy  •  Spinal Cord	2
+
+
+The contents of the suboccipital triangle include:
+
+■     posterior ramus of CI, ■     vertebral artery, and
+
+■     veins
+
+
+In the clinic
+
+Nerve injuries affecting superficial back muscles Weakness in the trapezius, caused by an interruption of the accessory nerve [XI], may appear as drooping of the shoulder, inability to raise the arm above the head because of impaired rotation of the scapula, or weakness in attempting to raise the shoulder (i.e., shrug the shoulder against resistance).
+A weakness in, or an inability to use, the latissimus dorsi, resulting from an injury to the thoracodorsal nerve, diminishes the capacity to pull the body upward while climbing or doing a pull-up.
+An injury to the dorsal scapular nerve, which innervates the rhomboids, may result in a lateral shift in the position of the scapula on the affected side (i.e., the normal position of the scapula is lost because of the affected muscle’s inability to prevent antagonistic muscles from pulling the scapula laterally).
+
+
+Cervical enlargement (of spinal cord)
+
+
+
+
+Pedicles of vertebrae
+
+
+
+
+SPINAL CORD
+
+
+The spinal cord extends from the foramen magnum to approximately the level of the disc between vertebrae LI and LII in adults, although it can end as high as vertebra TXII or as low as the disc between vertebrae LII and LIII (Fig. 2.53). In neonates, the spinal cord extends approxi-mately to vertebra LIII but can reach as low as vertebra LIV. The distal end of the cord (the conus medullaris) is cone
+
+
+Lumbosacral enlargement (of spinal cord)
+
+
+Conus medullaris
+
+
+
+End of spinal cord LI–LII
+
+
+
+shaped. A fine filament of connective tissue (the pial part of the filum terminale) continues inferiorly from the apex of the conus medullaris.
+The spinal cord is not uniform in diameter along its length. It has two major swellings or enlargements in regions associated with the origin of  spinal nerves that innervate the upper and lower limbs. A cervical enlarge-ment occurs in the region associated with the origins of spinal nerves C5 to T1, which innervate the upper limbs. A lumbosacral enlargement occurs in the region associ-ated with the origins of  spinal nerves L1 to S3, which innervate the lower limbs.
+
+
+
+
+
+Filum terminale
+
+
+Pial part
+
+
+
+
+
+
+Dural part
+
+
+
+Inferior part of arachnoid mater
+
+
+
+End of subarachnoid space SII
+
+
+
+The external surface of the spinal cord is marked by a number of fissures and sulci (Fig. 2.54):
+
+
+Fig. 2.53  Spinal cord.
+
+
+■     The anterior median fissure extends the length of the
+anterior surface.	101
+Back
+
+
+Central canal
+
+
+
+Posterior spinal artery
+
+Gray matter	Anterior spinal artery
+
+
+White matter
+
+Anterior median fissure
+
+
+
+Posterior median sulcus
+Posterolateral sulcus
+
+
+Segmental medullary arteries
+
+Vertebral artery
+Ascending cervical artery
+Deep cervical artery
+Costocervical trunk
+Thyrocervical trunk
+Subclavian artery
+
+
+
+
+
+
+
+
+
+Anterior median fissure
+
+Fig. 2.54  Features of the spinal cord.
+
+Segmental medullary arteries (branch from segmental spinal artery)
+
+Segmental spinal artery
+
+
+
+
+
+■     The posterior median sulcus extends along the pos-terior surface.
+■     The posterolateral sulcus on each side of the poste-rior surface marks where the posterior rootlets of spinal nerves enter the cord.
+
+Posterior intercostal artery
+
+
+
+Artery of Adamkiewicz (branch from segmental
+spinal artery)
+
+
+
+Internally, the cord has a small central canal surrounded by gray and white matter:
+
+
+Segmental spinal artery
+
+
+■     The gray matter is rich in nerve cell bodies, which form longitudinal  columns  along  the  cord,  and  in  cross section these columns form a characteristic H-shaped appearance in the central regions of the cord.
+■     The white matter surrounds the gray matter and is rich
+in nerve cell processes, which form large bundles or	Lateral sacral artery tracts that ascend and descend in the cord to other
+spinal cord levels or carry information to and from the brain.
+
+
+Vasculature Arteries
+The arterial supply to the spinal cord comes from two 102	sources (Fig. 2.55). It consists of:
+
+
+A
+
+Fig. 2.55  Arteries that supply the spinal cord. A. Anterior view of spinal cord (not all segmental spinal arteries are shown).
+Regional Anatomy  •  Spinal Cord	2
+
+
+
+Anterior radicular artery
+
+Segmental spinal artery	Posterior radicular artery
+
+
+Posterior spinal arteries
+
+Posterior radicular artery
+
+Anterior radicular artery
+
+
+
+
+
+
+Posterior branch of right posterior intercostal artery
+
+
+
+Segmental medullary artery
+
+Segmental medullary artery
+
+Segmental spinal artery
+
+
+Posterior branch of left posterior intercostal artery
+
+
+
+
+
+Anterior spinal artery
+
+Segmental spinal artery
+
+
+
+
+Left posterior intercostal artery
+
+
+
+Aorta
+
+
+
+B
+
+Fig. 2.55, cont’d  B. Segmental supply of spinal cord.
+
+
+
+
+■     longitudinally oriented vessels, arising superior to the cervical portion of  the cord, which descend on the surface of the cord; and
+■     feeder arteries that enter the vertebral canal through the intervertebral foramina at every level; these feeder vessels, or segmental spinal arteries, arise predomi-nantly from the vertebral and deep cervical arteries in the neck, the posterior intercostal arteries in the thorax, and the lumbar arteries in the abdomen.
+
+
+The longitudinal vessels consist of:
+
+■     a  single  anterior  spinal  artery,  which  originates within the cranial cavity as the union of two vessels that arise from the vertebral arteries—the resulting single anterior spinal artery passes inferiorly, approximately parallel to the anterior median fissure, along the surface of the spinal cord; and
+■     two posterior spinal arteries, which also originate in the cranial cavity, usually arising directly from a termi-
+
+
+
+After entering an intervertebral foramen, the segmental spinal arteries give rise to anterior and posterior radicu-lar arteries (Fig. 2.55). This occurs at every vertebral level. The radicular arteries follow, and supply, the anterior and posterior roots. At various vertebral levels, the seg-mental spinal arteries also give off segmental medul-lary arteries (Fig. 2.55). These vessels pass directly to the longitudinally oriented vessels, reinforcing these.
+
+nal branch of each vertebral artery (the posterior infe-rior  cerebellar  artery)—the  right  and  left  posterior spinal arteries descend along the spinal cord, each as two branches that bracket the posterolateral sulcus and the connection of posterior roots with the spinal cord.
+
+The anterior and posterior spinal arteries are reinforced
+along their length by eight to ten segmental medullary	103
+Back
+
+
+arteries (Fig. 2.55). The largest of  these is the arteria	■     One  midline  channel  parallels  the  anterior  median radicularis  magna  or  the  artery  of   Adamkiewicz           fissure.
+
+(Fig. 2.55). This vessel arises in the lower thoracic or upper lumbar region, usually on the left side, and reinforces the arterial supply to the lower portion of  the spinal cord, including the lumbar enlargement.
+
+■     One midline channel passes along the posterior median sulcus.
+
+These longitudinal channels drain into an extensive
+
+
+Veins
+Veins that drain the spinal cord form a number of longitu-dinal channels (Fig. 2.56):
+
+internal  vertebral  plexus  in  the  extradural  (epidural) space of the vertebral canal, which then drains into seg-mentally arranged vessels that connect with major sys-temic veins, such as the azygos system in the thorax. The internal vertebral plexus also communicates with intra-
+
+■     Two pairs of veins on each side bracket the connections	cranial veins. of the posterior and anterior roots to the cord.
+
+
+
+
+
+
+Posterior spinal vein
+
+
+
+
+
+
+
+Anterior spinal vein
+
+
+
+
+
+
+Dura mater Extradural fat
+
+
+
+
+
+
+Internal vertebral plexus
+
+
+
+Fig. 2.56  Veins that drain the spinal cord.
+
+
+
+
+
+
+
+
+104
+Regional Anatomy  •  Spinal Cord	2
+
+
+
+In the clinic
+
+Discitis
+The intervertebral discs are poorly vascularized; however, infection within the bloodstream can spread to the discs from the terminal branches of the spinal arteries within the vertebral body endplates, which lie immediately adjacent to the discs (Fig. 2.57). Common sources of infection include the lungs and urinary tract.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.57  MRI of the spine. There is discitis of the T10-T11 intervertebral disc with destruction of the adjacent endplates. There is also a prevertebral abscess and an epidural abscess, which impinges the cord.
+
+
+In the clinic
+
+Paraplegia and tetraplegia
+An injury to the spinal cord in the cervical portion of the vertebral column can lead to varying degrees of impairment of sensory and motor function (paralysis) in all 4 limbs, termed quadriplegia or tetraplegia. An injury in upper levels
+
+In the clinic
+
+Fractures of the atlas and axis
+Fractures of vertebra CI (the atlas) and vertebra CII (the axis) can potentially lead to the worst types of spinal cord injury including death and paralysis due to injury of the brainstem, which contains the cardiac and respiratory centers. The atlas is a closed ring with no vertebral body. Axial-loading injuries, such as hitting the head while diving into shallow water or hitting the head on the roof of a car in a motor vehicle accident, can cause a “burst” type of fracture, where the ring breaks at more than one site (Fig. 2.58). The British neurosurgeon, Geoffrey Jefferson, first described this fracture pattern in 1920, so these types of fractures are often called Jefferson fractures.
+Fractures of the axis usually occur due to severe hyperextension and flexion, which can result in fracture of the tip of the dens, base of the dens, or through the body of the atlas. In judicial hangings, there is hyperextension and distraction injury causing fracture through the atlas pedicles and spondylolisthesis of C2 on C3. This type of fracture is often called a hangman’s fracture.
+In many cases of upper neck injuries, even in the absence of fractures to the atlas or axis, there may be injury to the atlanto-axial ligaments, which can render the neck unstable and pose severe risk to the brainstem and upper spinal cord.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.58  CT at the level of CI demonstrates two breaks in the closed ring of the atlas following an axial-loading injury.
+
+
+
+
+of the cervical vertebral column can result in death because of loss of innervation to the diaphragm. An injury to the spinal cord below the level of TI can lead to varying degrees of impairment in motor and sensory function (paralysis) in the lower limbs, termed paraplegia.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+105
+Back
+
+
+
+
+Meninges
+Spinal dura mater
+The spinal dura mater is the outermost meningeal mem-brane and is separated from the bones forming the vertebral canal by an extradural space (Fig. 2.59). Superiorly, it is continuous with the inner meningeal layer of cranial dura mater at the foramen magnum of the skull. Inferiorly, the dural sac dramatically narrows at the level of the lower border of vertebra SII and forms an investing sheath for the pial part of  the filum terminale of  the spinal cord. This terminal cord-like extension of dura mater (the dural part of the filum terminale) attaches to the posterior surface of the vertebral bodies of the coccyx.
+As spinal nerves and their roots pass laterally, they are surrounded by tubular sleeves of dura mater, which merge with and become part of the outer covering (epineurium) of the nerves.
+
+Arachnoid mater
+The  arachnoid  mater  is  a  thin  delicate  membrane against, but not adherent to, the deep surface of the dura
+
+
+Posterior spinal artery
+
+mater (Fig. 2.59). It is separated from the pia mater by the subarachnoid space. The arachnoid mater ends at the level of vertebra SII (see Fig. 2.53).
+
+Subarachnoid space
+The subarachnoid space between the arachnoid and pia mater contains CSF (Fig. 2.59). The subarachnoid space around  the  spinal  cord  is  continuous  at  the  foramen magnum with the subarachnoid space surrounding the brain.  Inferiorly,  the  subarachnoid  space  terminates  at approximately the level of the lower border of vertebra SII (see Fig. 2.53).
+Delicate strands of tissue (arachnoid trabeculae) are continuous with the arachnoid mater on one side and the pia mater on the other; they span the subarachnoid space and  interconnect  the  two  adjacent  membranes.  Large blood vessels are suspended in the subarachnoid space by similar strands of material, which expand over the vessels to form a continuous external coat.
+The subarachnoid space extends farther inferiorly than the spinal cord. The spinal cord ends at approximately the  disc  between  vertebrae  LI  and  LII,  whereas  the
+
+Subarachnoid space
+
+Pia mater
+
+
+
+
+
+Recurrent meningeal nerves
+
+
+Denticulate ligament
+
+
+
+
+
+
+Arachnoid mater
+
+
+
+
+
+Anterior spinal artery
+
+
+
+
+
+Dura mater
+
+106	Fig. 2.59  Meninges.
+Regional Anatomy  •  Spinal Cord	2
+
+
+
+subarachnoid space extends to approximately the lower border of vertebra SII (see Fig. 2.53). The subarachnoid space is largest in the region inferior to the terminal end of the spinal cord, where it surrounds the cauda equina. As
+
+
+Arrangement of structures in the vertebral canal
+
+The vertebral canal is bordered:
+
+
+
+a consequence, CSF can be withdrawn from the subarach-noid space in the lower lumbar region without endanger-ing the spinal cord.
+
+Pia mater
+The spinal pia mater is a vascular membrane that firmly adheres to the surface of  the spinal cord (Fig. 2.59). It extends into the anterior median fissure and reflects as sleeve-like coatings onto posterior and anterior rootlets and roots as they cross the subarachnoid space. As the
+
+
+■     anteriorly by the bodies of the vertebrae, intervertebral discs, and posterior longitudinal ligament (Fig. 2.60);
+■     laterally, on each side by the pedicles and intervertebral foramina; and
+■     posteriorly by the laminae and ligamenta flava, and in the median plane the roots of the interspinous ligaments and vertebral spinous processes.
+
+Between the walls of the vertebral canal and the dural
+
+
+
+roots exit the space, the sleeve-like coatings reflect onto the arachnoid mater.
+On each side of the spinal cord, a longitudinally oriented sheet of  pia mater (the denticulate ligament) extends laterally from the cord toward the arachnoid and dura mater (Fig. 2.59).
+
+sac is an extradural space containing a vertebral plexus of veins embedded in fatty connective tissue.
+The vertebral spinous processes can be palpated through the skin in the midline in thoracic and lumbar regions of the back. Between the skin and spinous processes is a layer of superficial fascia. In lumbar regions, the adjacent
+
+
+
+
+■     Medially, each denticulate ligament is attached to the spinal cord in a plane that lies between the origins of the posterior and anterior rootlets.
+■     Laterally, each denticulate ligament forms a series of triangular extensions along its free border, with the apex of  each extension being anchored through the arachnoid mater to the dura mater.
+
+The lateral attachments of  the denticulate ligaments
+
+spinous processes and the associated laminae on either side of the midline do not overlap, resulting in gaps between adjacent vertebral arches.
+When carrying out a lumbar puncture (spinal tap), the needle passes between adjacent vertebral spinous processes, through the supraspinous and interspinous ligaments, and enters the extradural space. The needle continues through the dura and arachnoid mater and enters the subarachnoid space, which contains CSF.
+
+generally occur between the exit points of adjacent poste-rior and anterior rootlets. The ligaments function to posi-tion the spinal cord in the center of  the subarachnoid space.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+107
+Back
+
+
+Crura of diaphragm	Posterior longitudinal ligament
+
+Psoas
+
+
+
+
+
+Pedicle
+
+Aorta
+Cauda equina
+
+
+
+
+Vein
+
+Dura
+
+Internal vertebral plexus of veins in extradural space
+
+Ligamenta flava Interspinous ligament
+Supraspinous ligament Quadratus lumborum
+Erector spinae muscles
+
+
+
+
+
+Lumbar artery
+
+
+
+
+
+
+Intervertebral foramen
+
+Intervertebral disc
+
+
+Vertebra	Skin
+
+
+Lamina
+
+Fig. 2.60  Arrangement of structures in the vertebral canal and the back (lumbar region).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+108
+Regional Anatomy  •  Spinal Cord	2
+
+
+
+In the clinic
+
+Lumbar cerebrospinal fluid tap
+A lumbar tap (puncture) is carried out to obtain a sample of CSF for examination. In addition, passage of a needle or conduit into the subarachnoid space (CSF space) is used to inject antibiotics, chemotherapeutic agents, and anesthetics.
+The lumbar region is an ideal site to access the subarachnoid space because the spinal cord terminates around the level of the disc between vertebrae LI and LII in the adult. The subarachnoid space extends to the region of the lower border of the SII vertebra. There is therefore a large CSF-filled space containing lumbar and sacral nerve roots but no spinal cord.
+Depending on the clinician’s preference, the patient is placed in the lateral or prone position. A needle is passed in the midline in between the spinous processes into the extradural space. Further advancement punctures the dura and arachnoid mater to enter the subarachnoid space. Most needles push the roots away from the tip without causing the patient any symptoms. Once the needle is in the subarachnoid space, fluid can be
+
+
+
+
+
+
+Spinal nerves
+Each spinal nerve is connected to the spinal cord by poste-rior and anterior roots (Fig. 2.61):
+
+
+
+aspirated. In some situations, it is important to measure CSF pressure.
+Local anesthetics can be injected into the extradural space or the subarachnoid space to anesthetize the sacral and lumbar nerve roots. Such anesthesia is useful for operations on the pelvis and the legs, which can then be carried out without the need for general anesthesia. When procedures are carried out, the patient must be in the erect position and not lying on his or her side or in the head-down position. If a patient lies on his or her side, the anesthesia is likely to be unilateral. If the patient is placed in the head-down position, the anesthetic can pass cranially and potentially depress respiration.
+In some instances, anesthesiologists choose to carry out extradural anesthesia. A needle is placed through the skin, supraspinous ligament, interspinous ligament, and ligamenta flava into the areolar tissue and fat around the dura mater. Anesthetic agent is introduced and diffuses around the vertebral canal to anesthetize the exiting nerve roots and diffuse into the subarachnoid space.
+
+
+
+
+
+
+A spinal segment is the area of the spinal cord that gives rise to the posterior and anterior rootlets, which will form a single pair of spinal nerves. Laterally, the pos-
+
+
+
+
+■     The posterior root contains the processes of sensory neurons  carrying  information  to  the  CNS—the  cell bodies  of  the  sensory  neurons,  which  are  derived embryologically from neural crest cells, are clustered in a spinal ganglion at the distal end of  the posterior root, usually in the intervertebral foramen.
+
+terior and anterior roots on each side join to form a spinal nerve.
+Each  spinal  nerve  divides,  as  it  emerges  from  an intervertebral foramen, into two major branches: a small posterior  ramus  and  a  much  larger  anterior  ramus (Fig. 2.61):
+
+
+
+■     The anterior root contains motor nerve fibers, which carry signals away from the CNS—the cell bodies of the primary motor neurons are in anterior regions of the spinal cord.
+
+Medially, the posterior and anterior roots divide into
+
+
+■     The  posterior  rami  innervate  only  intrinsic  back muscles (the epaxial muscles) and an associated narrow strip of skin on the back.
+■     The  anterior  rami  innervate  most  other  skeletal muscles (the hypaxial muscles) of the body, including those of the limbs and trunk, and most remaining areas
+
+rootlets, which attach to the spinal cord.	of the skin, except for certain regions of the head.
+
+
+
+
+
+
+
+
+
+109
+Back
+
+
+
+
+Somatic motor	Intrinsic back muscles nerve fiber
+
+
+
+Somatic sensory nerve ending in skin
+
+
+Posterior root
+
+Spinal ganglion
+
+
+Spinal nerve
+
+Posterior ramus
+
+Posterior rootlets
+
+
+
+Anterior root
+
+Anterior ramus
+
+
+
+Somatic motor Anterior rootlets	nerve fiber
+
+
+All muscles except intrinsic back muscles
+
+Somatic sensory nerve ending in skin
+
+Fig. 2.61  Basic organization of a spinal nerve.
+
+
+
+
+
+Near the point of division into anterior and posterior rami, each spinal nerve gives rise to two to four small recurrent meningeal (sinuvertebral) nerves (see Fig. 2.59). These nerves reenter the intervertebral foramen to supply dura, ligaments, intervertebral discs, and blood vessels.
+All major somatic plexuses (cervical, brachial, lumbar, and sacral) are formed by anterior rami.
+Because the spinal cord is much shorter than the verte-bral column, the roots of spinal nerves become longer and pass more obliquely from the cervical to coccygeal regions of the vertebral canal (Fig. 2.62).
+
+In adults, the spinal cord terminates at a level approxi-mately between vertebrae LI and LII, but this can range between vertebra TXII and the disc between vertebrae LII and LIII. Consequently, posterior and anterior roots forming spinal nerves emerging between vertebrae in the lower regions of the vertebral column are connected to the spinal cord at higher vertebral levels.
+Below the end of  the spinal cord, the posterior and anterior roots of lumbar, sacral, and coccygeal nerves pass inferiorly to reach their exit points from the vertebral canal. This terminal cluster of roots is the cauda equina.
+
+
+
+
+
+
+
+110
+Regional Anatomy  •  Spinal Cord	2
+
+
+
+
+1
+
+2
+
+3
+
+4
+Cervical enlargement	5
+(of spinal cord)
+6
+
+7
+
+8
+
+1
+
+Pedicles of vertebrae	2
+3
+
+4 Spinal ganglion
+
+5
+
+
+C1
+
+C2 C3 C4
+C5 C6 C7 C8
+T1
+T2
+
+T3
+
+T4
+
+
+6	T5
+
+7	T6
+
+8	T7
+
+
+
+
+
+
+
+
+
+
+Lumbosacral enlargement (of spinal cord)
+
+9
+
+10
+
+11
+
+12
+
+1
+2
+3 4
+5 1 2 3
+4
+5
+1
+
+
+T8
+
+T9
+
+T10
+
+T11
+
+
+T12
+
+L1
+
+
+L2
+
+Cauda equina	L3
+
+L4
+
+L5
+
+
+
+S1
+S2 S3 S4 S5 Co
+
+
+Fig. 2.62  Course of spinal nerves in the vertebral canal.	111
+Back
+
+
+
+Nomenclature of spinal nerves
+There are approximately 31 pairs of  spinal nerves (Fig. 2.62), named according to their position with respect to associated vertebrae:
+
+■     eight cervical nerves—C1 to C8,
+■     twelve thoracic nerves—T1 to T12, ■     five lumbar nerves—L1 to L5,
+■     five sacral nerves—S1 to S5, ■     one coccygeal nerve—Co.
+
+In the clinic
+
+Herpes zoster
+Herpes zoster is the virus that produces chickenpox in children. In some patients the virus remains dormant in the cells of the spinal ganglia. Under certain circumstances, the virus becomes activated and travels
+along the neuronal bundles to the areas supplied by that nerve (the dermatome). A rash ensues, which is characteristically exquisitely painful. Importantly, this typical dermatomal distribution is characteristic of
+this disorder.
+
+
+The first cervical nerve (C1) emerges from the vertebral canal between the skull and vertebra CI (Fig. 2.63). There-fore cervical nerves C2 to C7 also emerge from the vertebral canal above their respective vertebrae. Because there are only seven cervical vertebrae, C8 emerges between verte-brae CVII and TI. As a consequence, all remaining spinal nerves,  beginning  with T1,  emerge  from  the  vertebral canal below their respective vertebrae.
+
+
+
+
+
+
+
+
+
+
+CI	C1
+
+Nerve C1 emerges between skull and CI vertebra
+
+
+C2
+
+C3
+
+C4	Nerves C2 to C7 emerge superior to pedicles
+C5
+
+C6
+
+
+
+Transition in	CVII nomenclature
+of nerves	TI
+
+
+Pedicle
+
+C7
+
+
+C8
+
+T1
+
+
+T2
+
+
+
+Nerve C8 emerges inferior to pedicle of CVII vertebra
+
+
+Nerves T1 to Co emerge inferior to pedicles of their respective vertebrae
+
+
+
+
+112	Fig. 2.63  Nomenclature of the spinal nerves.
+Regional Anatomy  •  Spinal Cord	2
+
+
+
+In the clinic
+
+Back pain—alternative explanations
+Back pain is an extremely common condition affecting almost all individuals at some stage during their life. It is of key clinical importance to identify whether the back pain relates to the vertebral column and its attachments or relates to other structures.
+The failure to consider other potential structures that may produce back pain can lead to significant mortality and morbidity. Pain may refer to the back from a number of organs situated in the retroperitoneum. Pancreatic pain in particular refers to the back and may be associated with pancreatic cancer and pancreatitis. Renal pain, which may be produced by stones in the renal collecting system or renal tumors, also typically refers to the back. More often than not this is usually unilateral; however, it can produce central
+
+
+
+posterior back pain. Enlarged lymph nodes in the pre- and para-aortic region may produce central posterior back pain and may be a sign of solid tumor malignancy, infection, or Hodgkin’s lymphoma. An enlarging abdominal aorta (abdominal aortic aneurysm) may cause back pain as it enlarges without rupture. Therefore it is critical to think of this structure as a potential cause of back pain, because treatment will be lifesaving. Moreover, a ruptured abdominal aortic aneurysm may also cause acute back pain in the first instance.
+In all patients back pain requires careful assessment not only of the vertebral column but also of the chest and abdomen in order not to miss other important anatomical structures that may produce signs and symptoms radiating to the back.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+113
+Back
+
+
+
+Surface anatomy Back surface anatomy
+Surface features of  the back are used to locate muscle groups for testing peripheral nerves, to determine regions of the vertebral column, and to estimate the approximate position of the inferior end of the spinal cord. They are also used to locate organs that occur posteriorly in the thorax and abdomen.
+
+
+
+Absence of lateral curvatures
+When viewed from behind, the normal vertebral column has no lateral curvatures. The vertical skin furrow between muscle masses on either side of  the midline is straight (Fig. 2.64).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A	B
+
+Fig. 2.64  Normal appearance of the back. A. In women. B. In men.
+
+
+
+
+
+
+
+
+
+
+
+
+
+114
+Surface Anatomy  •  Useful Nonvertebral Skeletal Landmarks	2
+
+
+
+
+Primary and secondary curvatures in the sagittal plane
+
+When viewed from the side, the normal vertebral column has  primary  curvatures  in  the  thoracic  and  sacral/ coccygeal regions and secondary curvatures in the cervical and lumbar regions (Fig. 2.65). The primary curvatures are  concave  anteriorly.  The  secondary  curvatures  are concave posteriorly.
+
+
+Useful nonvertebral skeletal landmarks
+A number of readily palpable bony features provide useful landmarks for defining muscles and for locating structures
+
+associated with the vertebral column. Among these fea-tures are the external occipital protuberance, the scapula, and the iliac crest (Fig. 2.66).
+The external occipital protuberance is palpable in the midline  at  the  back  of  the  head  just  superior  to  the hairline.
+The  spine,  medial  border,  and  inferior  angle  of  the scapula are often visible and are easily palpable.
+The iliac crest is palpable along its entire length, from the anterior superior iliac spine at the lower lateral margin of  the anterior abdominal wall to the posterior superior iliac spine near the base of the back. The position of the posterior superior iliac spine is often visible as a “sacral dimple” just lateral to the midline.
+
+
+
+
+
+
+
+
+
+Cervical region secondary curvature
+
+
+
+
+
+Thoracic region primary curvature
+
+
+
+
+
+
+Lumbar region secondary curvature
+
+
+
+Sacral/coccygeal region primary curvature
+
+
+Fig. 2.65  Normal curvatures of the vertebral column.
+
+
+
+
+
+
+
+
+115
+Back
+
+
+
+
+Position of external occipital protuberance
+
+
+
+
+Spine of scapula
+
+
+
+Medial border of scapula
+
+
+Inferior angle of scapula
+
+
+
+
+
+
+Iliac crest
+
+
+Posterior superior iliac spine
+
+
+
+
+
+
+Fig. 2.66  Back of a woman with major palpable bony landmarks indicated.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+116
+Surface Anatomy  •  How To Identify Specific Vertebral Spinous Processes	2
+
+
+
+
+How to identify specific vertebral spinous processes
+
+Identification of vertebral spinous processes (Fig. 2.67A) can be used to differentiate between regions of the vertebral column and facilitate visualizing the position of  deeper structures, such as the inferior ends of the spinal cord and subarachnoid space.
+
+The spinous process of  vertebra CII can be identified through deep palpation as the most superior bony protu-berance in the midline inferior to the skull.
+Most of the other spinous processes, except for that of vertebra CVII, are not readily palpable because they are obscured by soft tissue.
+
+
+
+
+Position of external occipital protuberance
+
+CII vertebral spinous process
+
+Root of spine of scapula	CVII vertebral spinous process TI vertebral spinous process
+
+TIII vertebral spinous process
+
+
+
+Inferior angle of scapula	TVII vertebral spinous process
+
+
+TXII vertebral spinous process
+
+
+Highest point of iliac crest
+
+Iliac crest
+
+Sacral dimple
+
+
+A
+
+
+LIV vertebral spinous process
+
+SII vertebral spinous process
+
+
+Tip of coccyx
+
+
+
+
+
+
+
+
+
+CVII vertebral spinous process
+TI vertebral
+spinous process	Ligamentum nuchae
+
+
+
+
+
+
+B	C
+
+Fig. 2.67  The back with the positions of vertebral spinous processes and associated structures indicated. A. In a man. B. In a woman with neck flexed. The prominent CVII and TI vertebral spinous processes are labeled. C. In a woman with neck flexed to accentuate the ligamentum
+nuchae.	117
+Back
+
+
+
+The spinous process of CVII is usually visible as a promi-nent eminence in the midline at the base of the neck (Fig. 2.67B), particularly when the neck is flexed.
+Extending between CVII and the external occipital pro-tuberance of the skull is the ligamentum nuchae, which is readily apparent as a longitudinal ridge when the neck is flexed (Fig. 2.67C).
+Inferior to the spinous process of  CVII is the spinous process of TI, which is also usually visible as a midline protuberance. Often it is more prominent than the spinous process of CVII (Fig. 2.67A,B).
+The root of the spine of the scapula is at the same level as the spinous process of  vertebra TIII, and the inferior angle of the scapula is level with the spinous process of vertebra TVII (Fig. 2.67A).
+The spinous process of vertebra TXII is level with the midpoint of a vertical line between the inferior angle of the scapula and the iliac crest (Fig. 2.67A).
+A horizontal line between the highest point of the iliac crest on each side crosses through the spinous process of vertebra LIV. The LIII and LV vertebral spinous processes can be palpated above and below the LIV spinous process, respectively (Fig. 2.67A).
+The sacral dimples that mark the position of the poste-rior superior iliac spine are level with the SII vertebral spinous process (Fig. 2.67A).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Inferior end of spinal cord (normally between
+LI and LII vertebra)
+
+
+Inferior end of subarachnoid space
+
+The tip of the coccyx is palpable at the base of the ver-tebral column between the gluteal masses (Fig. 2.67A).
+The tips of the vertebral spinous processes do not always lie in the same horizontal plane as their corresponding vertebral bodies. In thoracic regions, the spinous processes are long and sharply sloped downward so that their tips lie at the level of the vertebral body below. In other words, the tip of  the TIII vertebral spinous process lies at vertebral level TIV.
+In lumbar and sacral regions, the spinous processes are generally shorter and less sloped than in thoracic regions, and their palpable tips more closely reflect the position of their corresponding vertebral bodies. As a consequence, the palpable end of the spinous process of vertebra LIV lies at approximately the LIV vertebral level.
+
+
+Visualizing the inferior ends of the spinal cord and subarachnoid space
+
+The  spinal  cord  does  not  occupy  the  entire  length  of the  vertebral  canal.  Normally  in  adults,  it  terminates at  the  level  of  the  disc  between  vertebrae  LI  and  LII; however, it may end as high as TXII or as low as the disc between vertebrae LII and LIII. The subarachnoid space  ends  at  approximately  the  level  of  vertebra  SII (Fig. 2.68A).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+TXII vertebral spinous process
+
+
+LIV vertebral spinous process
+
+SII vertebral spinous process
+
+
+Tip of coccyx A
+
+118	Fig. 2.68  Back with the ends of the spinal cord and subarachnoid space indicated. A. In a man.
+Surface Anatomy  •  Identifying Major Muscles	2
+
+
+LIV vertebral spinous process	LV  vertebral spinous process
+
+
+
+
+
+
+Tip of coccyx
+
+
+
+Needle
+
+
+
+
+B
+
+Fig. 2.68, cont’d  Back with the ends of the spinal cord and subarachnoid space indicated. B. In a woman lying on her side in a fetal position, which accentuates the lumbar vertebral spinous processes and opens the spaces between adjacent vertebral arches. Cerebrospinal fluid can be withdrawn from the subarachnoid space in lower lumbar regions without endangering the spinal cord.
+
+
+
+
+
+
+Because the subarachnoid space can be accessed in the lower lumbar region without endangering the spinal cord, it is important to be able to identify the position of  the lumbar  vertebral  spinous  processes.  The  LIV  vertebral spinous process is level with a horizontal line between the highest points on the iliac crests. In the lumbar region, the palpable ends of the vertebral spinous processes lie opposite their corresponding vertebral bodies. The subarachnoid space can be accessed between vertebral levels LIII and LIV and between LIV and LV without endangering the spinal cord (Fig. 2.68B). The subarachnoid space ends at vertebral level SII, which is level with the sacral dimples marking the posterior superior iliac spines.
+
+Identifying major muscles
+A number of intrinsic and extrinsic muscles of the back can readily be observed and palpated. The largest of these are the trapezius and latissimus dorsi muscles (Fig. 2.69A
+
+
+Trapezius
+
+
+
+
+
+
+
+
+
+
+
+Latissimus dorsi
+
+
+
+A	Erector spinae muscles
+
+
+
+and 2.69B). Retracting the scapulae toward the midline can accentuate the rhomboid muscles (Fig. 2.69C), which lie deep to the trapezius muscle. The erector spinae muscles are visible as two longitudinal columns separated by a furrow in the midline (Fig. 2.69A).
+
+
+Fig. 2.69  Back muscles. A. In a man with latissimus dorsi, trapezius, and erector spinae muscles outlined.
+
+Continued
+
+
+
+
+
+
+119
+Back
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Latissimus dorsi
+
+
+
+B
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Rhomboid minor
+
+
+Rhomboid major
+
+
+
+C
+
+Fig. 2.69, cont’d Back muscles. B. In a man with arms abducted to accentuate the lateral margins of the latissimus dorsi muscles. C. In a woman with scapulae externally rotated and forcibly retracted to accentuate the rhomboid muscles.
+
+
+
+
+
+
+
+
+120
+Clinical Cases  •  Case 1	2
+
+
+Clinical cases
+
+
+
+Case 1
+
+CAUDA EQUINA SYNDROME
+
+A 50-year-old man was brought to the emergency department with severe lower back pain that had started several days ago. In the past 24 hours he has had two episodes of fecal incontinence and inability to pass urine and now reports numbness and weakness in both his legs.
+
+The attending physician performed a physical examination and found that the man had reduced strength during knee extension and when dorsiflexing his feet and toes. He also had reduced reflexes in his knees and ankles, numbness in the perineal (saddle) region, as well as reduced anal sphincter tone.
+
+The patient’s symptoms and physical examination findings raised serious concern for compression of multiple lumbar and sacral nerve roots in the spine, affecting both motor and sensory pathways. His reduced power in extending his knees and reduced knee reflexes was suggestive of compression of the L4 nerve roots. His reduced ability to dorsiflex his feet and toes was suggestive of compression of the L5 nerve roots. His reduced ankle reflexes was suggestive of compression of the S1 and S2 nerve roots, and his perineal numbness was suggestive of compression of the S3, S4, and S5 nerve roots.
+
+A diagnosis of cauda equina syndrome was made, and the patient was transferred for an urgent MRI scan, which confirmed the presence of a severely herniating L2-3 disc compressing the cauda equina, giving rise to the cauda equina syndrome (Fig. 2.70). The patient underwent surgical decompression of the cauda equina and made a full recovery.
+
+The collection of lumbar and sacral nerve roots beyond the conus medullaris has a horsetail-like appearance, from which
+
+
+
+it derives its name “cauda equina.” Compression of the cauda equina may be caused by a herniating disc (as in this case), fracture fragments following traumatic injury, tumor, abscess, or severe degenerative stenosis of the central canal.
+
+Cauda equina syndrome is classed as a surgical emergency to prevent permanent and irreversible damage to the compressed nerve roots.
+
+
+
+
+
+
+
+
+
+
+
+L2-3 intervertebral disc
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 2.70  MRI of the lumbar spine reveals posterior herniation of the L2-3 disc resulting in compression of the cauda equina filaments.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+121
+Back
+
+
+
+Case 2
+
+CERVICAL SPINAL CORD INJURY
+
+A 45-year-old man was involved in a serious car accident. On examination he had a severe injury to the cervical region of his vertebral column with damage to the spinal cord. In fact, his breathing became erratic and stopped.
+
+If the cervical spinal cord injury is above the level of C5, breathing is likely to stop. The phrenic nerve takes origin from C3, C4, and C5 and supplies the diaphragm. Breathing may not cease immediately if the lesion is just below C5, but does so as the cord becomes edematous and damage progresses superiorly. In addition, some respiratory and ventilatory exchange may occur by using neck muscles plus the sternocleidomastoid and trapezius muscles, which are innervated by the accessory nerve [XI].
+
+
+
+The patient was unable to sense or move his upper and lower limbs.
+
+The patient has paralysis of the upper and lower limbs and is therefore quadriplegic. If breathing is unaffected, the lesion is below the level of C5 or at the level of C5. The nerve supply to the upper limbs is via the brachial plexus, which begins at the C5 level. The site of the spinal cord injury is at or above the C5 level.
+
+It is important to remember that although the cord has been transected in the cervical region, the cord below this level is intact. Reflex activity may therefore occur below the injury, but communication with the brain is lost.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+122
+Clinical Cases  •  Case 4	2
+
+
+
+Case 3 PSOAS ABSCESS
+A 25-year-old woman complained of increasing lumbar back pain. Over the ensuing weeks she was noted to have an enlarging lump in the right groin, which was mildly tender to touch. On direct questioning, the patient also complained of a productive cough with sputum containing mucus and blood, and she had a mild temperature.
+
+The chest radiograph revealed a cavitating apical lung mass, which explains the pulmonary history.
+
+Given the age of the patient a primary lung cancer is unlikely. The hemoptysis (coughing up blood in the sputum) and the rest of the history suggest the patient has a lung infection. Given the chest radiographic findings of a cavity in the apex of the lung, a diagnosis of tuberculosis (TB) was made. This was confirmed by bronchoscopy and aspiration of pus, which was cultured.
+
+During the patient’s pulmonary infection, the tuberculous bacillus had spread via the blood to vertebra LI. The bone destruction began in the cancellous bone of the vertebral
+
+
+
+
+
+Case 4
+
+DISSECTING THORACIC ANEURYSM
+
+A 72-year-old fit and healthy man was brought to the emergency department with severe back pain beginning at the level of the shoulder blades and extending to the midlumbar region. The pain was of relatively acute onset and was continuous. The patient was able to walk to the gurney as he entered the ambulance; however, at the emergency department the patient complained of inability to use both legs.
+
+The attending physician examined the back thoroughly and found no significant abnormality. He noted that there was reduced sensation in both legs, and there was virtually no power in extensor or flexor groups. The patient was tachycardic, which was believed to be due to pain, and the blood pressure obtained in the ambulance measured
+120/80 mm Hg. It was noted that the patient’s current blood pressure was 80/40 mm Hg; however, the patient did not complain of typical clinical symptoms of hypotension.
+
+On first inspection, it is difficult to “add up” these clinical symptoms and signs. In essence we have a progressive paraplegia associated with severe back pain and an anomaly
+
+
+
+body close to the intervertebral discs. This disease progressed and eroded into the intervertebral disc, which became infected. The disc was destroyed, and the infected disc material extruded around the disc anteriorly and passed into the psoas muscle sheath. This is not an uncommon finding for a tuberculous infection of the lumbar portion of the vertebral column.
+
+As the infection progressed, the pus spread within the psoas muscle sheath beneath the inguinal ligament to produce a hard mass in the groin. This is a typical finding for a psoas abscess.
+
+Fortunately for the patient, there was no evidence of any damage within the vertebral canal.
+
+The patient underwent a radiologically guided drainage of the psoas abscess and was treated for over 6 months with a long-term antibiotic regimen. She made an excellent recovery with no further symptoms, although the cavities within the lungs remain. It healed with sclerosis.
+
+
+
+
+
+
+
+
+
+in blood pressure measurements, which are not compatible with the clinical state of the patient.
+
+It was deduced that the blood pressure measurements were obtained in different arms, and both were reassessed.
+
+The blood pressure measurements were true. In the right arm the blood pressure measured 120/80 mm Hg and in the left arm the blood pressure measured 80/40 mm Hg. This would imply a deficiency of blood to the left arm.
+
+The patient was transferred from the emergency department to the CT scanner, and a scan was performed that included the chest, abdomen, and pelvis.
+
+The CT scan demonstrated a dissecting thoracic aortic aneurysm. Aortic dissection occurs when the tunica intima and part of the tunica media of the wall of the aorta become separated from the remainder of the tunica media and the tunica adventitia of the aorta wall. This produces a false lumen. Blood passes not only in the true aortic lumen but also through a small hole into the wall of the aorta and into the false lumen. It often reenters the true aortic lumen
+
+(continues)
+
+
+
+122.e1
+Back
+
+
+
+Case 4—cont’d
+
+inferiorly. This produces two channels through which blood may flow. The process of the aortic dissection produces considerable pain for the patient and is usually of rapid onset. Typically the pain is felt between the shoulder blades and radiating into the back, and although the pain is not from the back musculature or the vertebral column, careful consideration of structures other than the back should always be sought.
+
+The difference in the blood pressure between the two arms indicates the level at which the dissection has begun. The “point of entry” is proximal to the left subclavian artery. At this level a small flap has been created, which limits the blood flow to the left upper limb, giving the low blood pressure recording. The brachiocephalic trunk has not been affected by the aortic dissection, and hence blood flow remains appropriate to the right upper limb.
+
+
+
+
+
+Case 5 SACRAL TUMOR
+A 55-year-old woman came to her physician with sensory alteration in the right gluteal (buttock) region and in the intergluteal (natal) cleft. Examination also demonstrated low-grade weakness of the muscles of the foot and subtle weakness of the extensor hallucis longus, extensor digitorum longus, and fibularis tertius on the right. The patient also complained of some mild pain symptoms posteriorly in the right gluteal region.
+
+A lesion was postulated in the left sacrum.
+
+Pain in the right sacro-iliac region could easily be attributed to the sacro-iliac joint, which is often very sensitive to pain. The weakness of the intrinsic muscles of the foot and the extensor hallucis longus, extensor digitorum longus, and fibularis tertius muscles raises the possibility of an abnormality affecting the nerves exiting the sacrum and possibly the lumbosacral junction. The altered sensation around the gluteal region toward the anus would also support these anatomical localizing features.
+
+An X-ray was obtained of the pelvis.
+
+The X-ray appeared on first inspection unremarkable. However, the patient underwent further investigation, including CT and MRI, which demonstrated a large
+
+
+
+The paraplegia was caused by ischemia to the spinal cord.
+
+The blood supply to the spinal cord is from a single anterior spinal artery and two posterior spinal arteries. These arteries are fed via segmental spinal arteries at every vertebral level. There are a number of reinforcing arteries (segmental medullary arteries) along the length of the spinal cord—the largest of which is the artery of Adamkiewicz. This artery of Adamkiewicz, a segmental medullary artery, typically arises from the lower thoracic or upper lumbar region, and unfortunately during this patient’s aortic dissection, the origin of this vessel was disrupted. This produces acute spinal cord ischemia and has produced the paraplegia in the patient.
+
+Unfortunately, the dissection extended, the aorta ruptured, and the patient succumbed.
+
+
+
+
+
+
+
+destructive lesion involving the whole of the left sacrum extending into the anterior sacral foramina at the S1, S2, and S3 levels. Interestingly, plain radiographs of the sacrum may often appear normal on first inspection, and further imaging should always be sought in patients with a suspected sacral abnormality.
+
+The lesion was expansile and lytic.
+
+Most bony metastases are typically nonexpansile. They may well erode the bone, producing lytic type of lesions, or may become very sclerotic (prostate metastases and breast metastases). From time to time we see a mixed pattern of lytic and sclerotic.
+
+There are a number of uncommon instances in which certain metastases are expansile and lytic. These typically occur in renal metastases and may be seen in multiple myeloma. The anatomical importance of these specific tumors is that they often expand and impinge upon other structures. The expansile nature of this patient’s tumor within the sacrum was the cause for compression of the sacral nerve roots, producing her symptoms.
+
+The patient underwent a course of radiotherapy, had the renal tumor excised, and is currently undergoing a course of chemoimmunotherapy.
+
+
+
+
+
+122.e2
+Conceptual Overview  •  General Description	3
+
+
+Conceptual overview GENERAL DESCRIPTION
+
+The thoraxis an irregularly shaped cylinder with a narrow	The  thoracic  cavity  enclosed  by  the  thoracic  wall opening (superior thoracic aperture) superiorly and a rela-       and   the   diaphragm   is   subdivided   into   three   major tively large opening (inferior thoracic aperture) inferiorly       compartments:
+
+(Fig. 3.1). The superior thoracic aperture is open, allowing continuity with the neck; the inferior thoracic aperture is closed by the diaphragm.
+The musculoskeletal wall of the thorax is flexible and
+
+
+■     a left and a right pleural cavity, each surrounding a lung, and
+■     the mediastinum.
+
+consists  of  segmentally  arranged  vertebrae,  ribs,  and muscles and the sternum.
+
+
+Superior thoracic aperture
+Vertebral column
+
+Mediastinum
+
+
+Right pleural cavity	Left pleural cavity
+Rib I
+
+
+Manubrium of sternum
+
+
+Sternal angle
+
+
+
+
+
+
+Body of sternum
+
+
+
+
+Ribs
+
+
+
+
+Xiphoid process
+
+Diaphragm
+
+
+Inferior thoracic aperture
+
+
+
+
+
+
+
+Fig. 3.1  Thoracic wall and cavity.	125
+Thorax
+
+
+
+The mediastinum is a thick, flexible soft tissue partition oriented longitudinally in a median sagittal position. It contains the heart, esophagus, trachea, major nerves, and major systemic blood vessels.
+The pleural cavities are completely separated from each other by the mediastinum. Therefore abnormal events in one pleural cavity do not necessarily affect the other cavity. This also means that the mediastinum can be entered surgically without opening the pleural cavities.
+Another important feature of the pleural cavities is that they extend above the level of rib I. The apex of each lung actually extends into the root of  the neck. As a conse-
+
+
+Conduit
+The mediastinum acts as a conduit for structures that pass completely through the thorax from one body region to another and for structures that connect organs in the thorax to other body regions.
+The esophagus, vagus nerves, and thoracic duct pass through  the  mediastinum  as  they  course  between  the abdomen and neck.
+The phrenic nerves, which originate in the neck, also pass through the mediastinum to penetrate and supply the diaphragm.
+
+quence, abnormal events in the root of the neck can involve	Other   structures   such   as   the   trachea,   thoracic
+
+the adjacent pleura and lung, and events in the adjacent pleura and lung can involve the root of the neck.
+
+
+FUNCTIONS
+Breathing
+
+aorta, and superior vena cava course within the media-stinum en route to and from major visceral organs in the thorax.
+
+COMPONENT PARTS
+Thoracic wall
+
+
+
+One of  the most important functions of  the thorax is breathing. The thorax not only contains the lungs but also
+
+The  thoracic  wall  consists  of  skeletal  elements  and muscles (Fig. 3.1):
+
+
+
+provides the machinery necessary—the diaphragm, tho-racic wall, and ribs—for effectively moving air into and out of the lungs.
+Up  and  down  movements  of   the  diaphragm  and changes in the lateral and anterior dimensions of  the thoracic  wall,  caused  by  movements  of  the  ribs,  alter the volume of  the thoracic cavity and are key elements in breathing.
+
+Protection of vital organs
+The thorax houses and protects the heart, lungs, and great vessels. Because of the upward domed shape of the dia-
+
+
+■     Posteriorly, it is made up of twelve thoracic vertebrae and their intervening intervertebral discs;
+■     Laterally, the wall is formed by ribs (twelve on each side) and three layers of flat muscles, which span the inter-costal spaces between adjacent ribs, move the ribs, and provide support for the intercostal spaces;
+■     Anteriorly, the wall is made up of the sternum, which consists of the manubrium of sternum, body of sternum, and xiphoid process.
+
+The manubrium of sternum, angled posteriorly on the
+
+
+
+phragm, the thoracic wall also offers protection to some important abdominal viscera.
+Much of the liver lies under the right dome of the dia-phragm, and the stomach and spleen lie under the left. The posterior aspects of the superior poles of the kidneys lie on the diaphragm and are anterior to rib XII, on the right, and to ribs XI and XII, on the left.
+
+body of sternum at the manubriosternal joint, forms the sternal angle, which is a major surface landmark used by clinicians  in  performing  physical  examinations  of  the thorax.
+The anterior (distal) end of  each rib is composed of costal cartilage, which contributes to the mobility and elasticity of the wall.
+
+
+
+
+
+
+
+
+
+
+
+
+126
+Conceptual Overview  •  Component Parts	3
+
+
+
+All ribs articulate with thoracic vertebrae posteriorly. Most ribs (from rib II to IX) have three articulations with the vertebral column. The head of  each rib articulates with the body of its own vertebra and with the body of the
+
+XI and XII are called floating ribs because they do not articulate with other ribs, costal cartilages, or the sternum. Their costal cartilages are small, only covering their tips.
+The skeletal framework of  the thoracic wall provides
+
+
+
+vertebra above (Fig. 3.2). As these ribs curve posteriorly, each also articulates with the transverse process of  its
+
+extensive  attachment  sites  for  muscles  of   the  neck, abdomen, back, and upper limbs.
+
+
+
+vertebra.
+Anteriorly, the costal cartilages of ribs I to VII articulate with the sternum.
+The costal cartilages of ribs VIII to X articulate with the inferior margins of the costal cartilages above them. Ribs
+
+A number of these muscles attach to ribs and function as accessory respiratory muscles; some of them also stabi-lize the position of the first and last ribs.
+
+
+
+
+
+
+
+Superior articular process	Superior costal facet
+
+
+Costal facet of transverse process
+
+
+
+
+
+
+
+
+
+Inferior articular process
+
+Intervertebral disc	Sternum
+
+Vertebral body
+
+
+Rib V	Inferior costal facet
+
+
+
+
+
+Costal cartilage
+
+
+Fig. 3.2  Joints between ribs and vertebrae.
+
+
+
+
+
+
+
+
+
+
+
+
+127
+Thorax
+
+
+
+
+Superior thoracic aperture
+Completely surrounded by skeletal elements, the superior thoracic aperture consists of  the body of  vertebra TI posteriorly, the medial margin of rib I on each side, and the manubrium anteriorly.
+The superior margin of the manubrium is in approxi-mately the same horizontal plane as the intervertebral disc
+
+Inferior thoracic aperture
+The inferior thoracic aperture is large and expandable. Bone, cartilage, and ligaments form its margin (Fig. 3.4A). The  inferior  thoracic  aperture  is  closed  by  the  dia-phragm, and structures passing between the abdomen and
+thorax pierce or pass posteriorly to the diaphragm. Skeletal elements of the inferior thoracic aperture are:
+
+
+
+between vertebrae TII and TIII.
+The first ribs slope inferiorly from their posterior articu-lation with vertebra TI to their anterior attachment to the manubrium. Consequently, the plane of the superior thoracic aperture is at an oblique angle, facing somewhat anteriorly.
+At the superior thoracic aperture, the superior aspects of the pleural cavities, which surround the lungs, lie on
+
+
+■     the body of vertebra TXII posteriorly,
+■     rib XII and the distal end of rib XI posterolaterally,
+■     the distal cartilaginous ends of ribs VII to X, which unite to form the costal margin anterolaterally, and
+■     the xiphoid process anteriorly.
+
+The joint between the costal margin and sternum lies
+
+
+
+either side of the entrance to the mediastinum (Fig. 3.3). Structures that pass between the upper limb and thorax
+pass over rib I and the superior part of the pleural cavity as they enter and leave the mediastinum. Structures that pass between the neck and head and the thorax pass more vertically through the superior thoracic aperture.
+
+roughly in the same horizontal plane as the intervertebral disc between vertebrae TIX and TX. In other words, the posterior margin of the inferior thoracic aperture is inferior to the anterior margin.
+When viewed anteriorly, the inferior thoracic aperture is tilted superiorly.
+
+
+
+
+
+
+
+Esophagus	Trachea	Veins Common carotid artery                                                                                                                            Nerves
+
+Vertebra TI	Arteries
+
+
+Superior thoracic aperture
+
+Rib I
+
+
+Apex of right lung
+
+
+
+
+Subclavian artery
+and vein
+
+
+
+
+
+
+Internal jugular vein
+
+
+
+
+
+
+Manubrium of sternum
+
+
+Pleaural cavity (lung)
+
+Trachea
+
+Esophagus
+
+
+Rib II
+
+
+
+
+
+128	Fig. 3.3  Superior thoracic aperture.
+Conceptual Overview  •  Component Parts	3
+
+
+
+
+
+
+
+Right dome
+
+
+
+
+Xiphoid process
+
+Inferior thoracic aperture
+
+Distal cartilaginous ends of ribs VII to X; costal margins
+
+Rib XI Rib XII
+Vertebra TXII
+
+A
+
+Central tendon
+
+
+Left dome
+
+
+
+Esophageal hiatus
+
+Aortic hiatus
+
+B
+
+
+Fig. 3.4  A. Inferior thoracic aperture. B. Diaphragm.
+
+
+
+
+
+Diaphragm
+The musculotendinous diaphragm seals the inferior tho-racic aperture (Fig. 3.4B).
+Generally, muscle fibers of the diaphragm arise radially, from the margins of  the inferior thoracic aperture, and converge into a large central tendon.
+Because of  the oblique angle of  the inferior thoracic aperture, the posterior attachment of  the diaphragm is inferior to the anterior attachment.
+
+
+The diaphragm is not flat; rather, it “balloons” superi-orly, on both the right and left sides, to form domes. The right dome is higher than the left, reaching as far as rib V. As the diaphragm contracts, the height of the domes
+decreases and the volume of the thorax increases.
+The esophagus and inferior vena cava penetrate the diaphragm; the aorta passes posterior to the diaphragm.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+129
+Thorax
+
+
+
+
+Mediastinum
+The mediastinum is a thick midline partition that extends from  the  sternum  anteriorly  to  the  thoracic  vertebrae posteriorly, and from the superior thoracic aperture to the inferior thoracic aperture.
+A horizontal plane passing through the sternal angle and the intervertebral disc between vertebrae TIV and TV separates the mediastinum into superior and inferior parts (Fig. 3.5). The inferior part is further subdivided by the pericardium, which encloses the pericardial cavity sur-rounding the heart. The pericardium and heart constitute the middle mediastinum.
+The anterior mediastinum lies between the sternum and the pericardium; the posterior mediastinum lies between the pericardium and thoracic vertebrae.
+
+
+Pleural cavities
+The two pleural cavities are situated on either side of the mediastinum (Fig. 3.6).
+
+Each pleural cavity is completely lined by a mesothelial membrane called the pleura.
+During development, the lungs grow out of the media-stinum, becoming surrounded by the pleural cavities. As a result, the outer surface of each organ is covered by pleura. Each lung remains attached to the mediastinum by a root formed by the airway, pulmonary blood vessels, lym-
+phatic tissues, and nerves.
+The pleura lining the walls of the cavity is the parietal pleura, whereas that reflected from the mediastinum at the roots and onto the surfaces of  the lungs is the visceral pleura. Only a potential space normally exists between the visceral pleura covering lung and the parietal pleura lining the wall of the thoracic cavity.
+The lung does not completely fill the potential space of the  pleural  cavity,  resulting  in  recesses,  which  do  not contain  lung  and  are  important  for  accommodating changes in lung volume during breathing. The costodia-phragmatic recess, which is the largest and clinically most important recess, lies inferiorly between the thoracic wall and diaphragm.
+
+
+
+
+
+
+
+
+
+
+
+Sternal angle	I	Rib I
+
+
+Superior mediastinum
+IV
+
+V	Anterior mediastinum
+
+
+Middle mediastinum
+
+
+Posterior mediastinum Inferior mediastinum
+X
+
+Diaphragm
+XII
+
+
+
+
+
+130	Fig. 3.5  Subdivisions of the mediastinum.
+Conceptual Overview  •  Component Parts	3
+
+
+
+
+
+
+
+
+
+
+
+
+Apex of right lung
+
+
+
+
+Right main bronchus
+
+Trachea
+
+
+Left pleural cavity surrounding left lung
+
+
+
+
+
+Parietal pleura
+
+
+Visceral pleura	Mediastinum
+
+Right pleural cavity
+
+
+
+
+
+
+
+
+Costodiaphragmatic recess
+
+
+Diaphragm
+
+
+
+
+
+
+
+
+
+Fig. 3.6  Pleural cavities.
+
+
+
+
+
+
+
+
+131
+Thorax
+
+
+
+RELATIONSHIP TO OTHER REGIONS Neck
+The superior thoracic aperture opens directly into the root of the neck (Fig. 3.7).
+The  superior  aspect  of  each  pleural  cavity  extends
+
+which extends anteriorly from the superior margin of the scapula.
+The base of the axillary inlet’s triangular opening is the lateral margin of rib I.
+Large blood vessels passing between the axillary inlet and superior thoracic aperture do so by passing over rib I.
+
+approximately 2 to 3 cm above rib I and the costal cartilage	Proximal   parts   of   the   brachial   plexus   also   pass
+
+into the neck. Between these pleural extensions, major visceral structures pass between the neck and superior mediastinum. In the midline, the trachea lies immediately anterior to the esophagus. Major blood vessels and nerves pass in and out of  the thorax at the superior thoracic aperture anteriorly and laterally to these structures.
+
+Upper limb
+
+between the neck and upper limb by passing through the axillary inlet.
+
+Abdomen
+The diaphragm separates the thorax from the abdomen. Structures that pass between the thorax and abdomen either penetrate the diaphragm or pass posteriorly to it (Fig. 3.8):
+
+
+
+An axillary inlet, or gateway to the upper limb, lies on each side of the superior thoracic aperture. These two axil-lary inlets and the superior thoracic aperture communicate superiorly with the root of the neck (Fig. 3.7).
+Each axillary inlet is formed by:
+
+
+■     The inferior vena cava pierces the central tendon of the diaphragm to enter the right side of the media-stinum near vertebral level TVIII.
+■     The esophagus penetrates the muscular part of  the diaphragm  to  leave  the  mediastinum  and  enter  the
+
+
+
+■     the superior margin of the scapula posteriorly, ■     the clavicle anteriorly, and
+■     the lateral margin of rib I medially.
+
+abdomen just to the left of  the midline at vertebral level TX.
+
+
+
+The apex of  each triangular inlet is directed laterally and is formed by the medial margin of the coracoid process,
+
+
+Inferior vena cava
+
+Esophagus
+
+
+
+Caval opening (vertebral level TVIII)
+
+
+Aorta
+Central tendon of diaphragm
+
+
+
+
+Superior thoracic aperture
+
+Esophagus
+
+Brachial plexus
+
+Rib I
+
+Scapula
+
+Axillary inlet
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Subclavian artery and vein
+
+
+
+Trachea
+Clavicle
+
+
+
+Coracoid process
+
+LI
+Aortic hiatus (vertebral level TXII)
+
+
+Esophageal hiatus (vertebral level TX)
+
+
+132	Fig. 3.7  Superior thoracic aperture and axillary inlet.	Fig. 3.8  Major structures passing between abdomen and thorax.
+Conceptual Overview  •  Relationship to Other Regions	3
+
+
+
+■     The aorta passes posteriorly to the diaphragm at the midline at vertebral level TXII.
+■     Numerous  other  structures  that  pass  between  the thorax and abdomen pass through or posterior to the diaphragm.
+
+sternum to supply anterior aspects of the thoracic wall. Those branches associated mainly with the second to fourth intercostal spaces also supply the anteromedial parts of each breast.
+■     Lymphatic vessels from the medial part of  the breast
+
+
+
+
+Breast
+The breasts, consisting of  mammary glands, superficial fascia, and overlying skin, are in the pectoral region on each side of the anterior thoracic wall (Fig. 3.9).
+Vessels,  lymphatics,  and  nerves  associated  with  the breast are as follows:
+
+accompany  the  perforating  arteries  and  drain  into the parasternal nodes on the deep surface of the thoracic wall.
+■     Vessels and lymphatics associated with lateral parts of the breast emerge from or drain into the axillary region of the upper limb.
+■     Lateral and anterior branches of  the fourth to sixth
+
+
+■     Branches from the internal thoracic arteries and veins perforate the anterior chest wall on each side of  the
+
+intercostal nerves carry general sensation from the skin of the breast.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Axillary process
+
+
+
+Axillary lymph nodes
+
+
+
+Internal
+thoracic artery	Pectoralis major
+
+
+
+Second, third, and fourth anterior perforating branches of internal thoracic artery
+
+
+Parasternal lymph nodes
+
+
+
+
+
+
+Fourth thoracic intercostal nerve
+
\ No newline at end of file