Anatomy_Gray

Anatomy_Gray. 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. In the clinic


Anatomy_Gray

Anatomy_Gray. 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.


Anatomy_Gray

Anatomy_Gray. 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. In the clinic 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.


Anatomy_Gray

Anatomy_Gray. 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 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 tend to occur in specific muscle groups and usually are related to a sudden exertion and muscle disruption. They typically occur in athletes.


Anatomy_Gray

Anatomy_Gray. In the clinic 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. In the clinic


Anatomy_Gray

Anatomy_Gray. In the clinic 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. In the clinic


Anatomy_Gray

Anatomy_Gray. In the clinic 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.


Anatomy_Gray

Anatomy_Gray. 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. In the clinic 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.


Anatomy_Gray

Anatomy_Gray. 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. In the clinic


Anatomy_Gray

Anatomy_Gray. In the clinic 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). In the clinic


Anatomy_Gray

Anatomy_Gray. In the clinic 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. In the clinic


Anatomy_Gray

Anatomy_Gray. In the clinic 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.


Anatomy_Gray

Anatomy_Gray. 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. 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. 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.


Anatomy_Gray

Anatomy_Gray. 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.


Anatomy_Gray

Anatomy_Gray. 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). Although appendicitis is common, other disorders, for example of the bowel and pelvis, may produce similar symptoms. The Body In the clinic—cont’d


Anatomy_Gray

Anatomy_Gray. Although appendicitis is common, other disorders, for example of the bowel and pelvis, may produce similar symptoms. The Body In the clinic—cont’d 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.


Anatomy_Gray

Anatomy_Gray. 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 vertebral column is positioned posteriorly in the body at the midline. When viewed laterally, it has a number of curvatures (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 lumbar regions, lower back problems are common.


Anatomy_Gray

Anatomy_Gray. As stresses on the back increase from the cervical to lumbar regions, lower back problems are common. Muscles of the back consist of extrinsic and intrinsic groups: 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). Although the amount of movement between any two vertebrae is limited, the effects between vertebrae are additive along the length of the vertebral column. Also, freedom 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.


Anatomy_Gray

Anatomy_Gray. In the cervical region, the first two vertebrae and associated muscles are specifically modified to support and position 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.


Anatomy_Gray

Anatomy_Gray. The major bones of the back are the 33 vertebrae (Fig. 2.5). The number and specific characteristics of the vertebrae 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 vertebrae. 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. A typical vertebra consists of a vertebral body and a vertebral arch (Fig. 2.6). The vertebral body is anterior and is the major weightbearing component of the bone. It increases in size from vertebra CII to vertebra LV. Fibrocartilaginous intervertebral discs separate the vertebral bodies of adjacent vertebrae.


Anatomy_Gray

Anatomy_Gray. 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: 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 inferiorly from the roof of the vertebral arch.


Anatomy_Gray

Anatomy_Gray. A spinous process projects posteriorly and generally inferiorly from the roof of the vertebral arch. 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. Each vertebra also contains rib elements. In the thorax, these costal elements are large and form ribs, which articulate 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 in the back can be classified as extrinsic or intrinsic based on their embryological origin and type of innervation (Fig. 2.7).


Anatomy_Gray

Anatomy_Gray. Muscles in the back can be classified as extrinsic or intrinsic based on their embryological origin and type of innervation (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 superficial group of these muscles is related to the upper limbs, while the intermediate layer of muscles is associated with 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 vertebral column. The spinal cord lies within a bony canal formed by adjacent vertebrae and soft tissue elements (the vertebral canal) (Fig. 2.8): The anterior wall is formed by the vertebral bodies of the vertebrae, intervertebral discs, and associated ligaments.


Anatomy_Gray

Anatomy_Gray. 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. Within the vertebral canal, the spinal cord is surrounded by a series of three connective tissue membranes (the meninges): The pia mater is the innermost membrane and is intimately associated with the surface of the spinal cord. The second membrane, the arachnoid mater, is separated 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 from surrounding bone by an extradural (epidural) space containing loose connective tissue, fat, and a venous plexus.


Anatomy_Gray

Anatomy_Gray. In the vertebral canal, the dura mater is separated from surrounding bone by an extradural (epidural) space containing loose connective tissue, fat, and a venous plexus. 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). 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: 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 exclusively, by cranial nerves.


Anatomy_Gray

Anatomy_Gray. The anterior rami form the major somatic plexuses (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. 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). 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 cervical vertebrae and pass through the foramen magnum to participate, with the internal carotid arteries, in supplying blood to the brain. Thorax, abdomen, and pelvis


Anatomy_Gray

Anatomy_Gray. 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. 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.


Anatomy_Gray

Anatomy_Gray. 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 increasingly 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. 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:


Anatomy_Gray

Anatomy_Gray. 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 disc between the vertebral bodies of the adjacent vertebrae. 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. 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 head. Parts of dermatomes innervated by the posterior rami of spinal nerves are shown in Fig. 2.13.


Anatomy_Gray

Anatomy_Gray. Skeletal components of the back consist mainly of the vertebrae and associated intervertebral discs. The skull, scapulae, pelvic bones, and ribs also contribute to the bony framework of the back and provide sites for muscle attachment. There are approximately 33 vertebrae, which are subdivided into five groups based on morphology and location (Fig. 2.14): The seven cervical vertebrae between the thorax and skull are characterized mainly by their small size and the presence of a foramen in each transverse process (Figs. 2.14 and 2.15). 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.


Anatomy_Gray

Anatomy_Gray. Inferior to the thoracic vertebrae are five lumbar vertebrae, which form the skeletal support for the posterior abdominal wall and are characterized by their large size (Figs. 2.14 and 2.17). 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 intersegmentally 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 spinal nerves develop segmentally and pass between the forming vertebrae.


Anatomy_Gray

Anatomy_Gray. A typical vertebra consists of a vertebral body and a posterior 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 intervertebral discs and ligaments. The size of vertebral bodies increases inferiorly as the amount of weight supported 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 continuous, through the foramen magnum of the skull, with the cranial cavity of the head. The vertebral arch of each vertebra consists of pedicles and laminae (Fig. 2.19): The two pedicles are bony pillars that attach the vertebral arch to the vertebral body.


Anatomy_Gray

Anatomy_Gray. The vertebral arch of each vertebra consists of pedicles and laminae (Fig. 2.19): The two pedicles are bony pillars that attach the vertebral 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 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 articulation 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.


Anatomy_Gray

Anatomy_Gray. Between the vertebral body and the origin of the articular processes, each pedicle is notched on its superior and inferior surfaces. These superior and inferior vertebral notches participate in forming intervertebral foramina. The seven cervical vertebrae are characterized by their small size and by the presence of a foramen in each transverse process. A typical cervical vertebra has the following features (Fig. 2.20A): The vertebral body is short in height and square shaped 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 and axis—are specialized to accommodate movement of the head.


Anatomy_Gray

Anatomy_Gray. The spinous process is short and bifid. The vertebral foramen is triangular. The first and second cervical vertebrae—the atlas and axis—are specialized to accommodate movement of the head. 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 between CI and CII. When viewed from above, the atlas is ring shaped and composed of two lateral masses interconnected 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 inferior articular surfaces are almost circular and flat.


Anatomy_Gray

Anatomy_Gray. 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 articular 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.


Anatomy_Gray

Anatomy_Gray. The axis is characterized by the large tooth-like 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 circular impressions that serve as attachment sites for strong alar ligaments, one on each side, which connect the dens to the medial surfaces of the occipital condyles. These alar ligaments check excessive rotation of the head and atlas relative to the axis. 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.


Anatomy_Gray

Anatomy_Gray. 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. 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 processes 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 cylindrical and the vertebral foramen is triangular in shape and larger than in the thoracic vertebrae.


Anatomy_Gray

Anatomy_Gray. The vertebral body of a typical lumbar vertebra is cylindrical and the vertebral foramen is triangular in shape and larger than in the thoracic vertebrae. 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 concave anterior surface and a correspondingly convex posterior surface. It articulates above with vertebra LV 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 incomplete near the inferior end of the sacrum.


Anatomy_Gray

Anatomy_Gray. The posterior wall of the vertebral canal may be incomplete near the inferior end of the sacrum. 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 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: posteriorly by the zygapophysial joint between the articular processes of the two vertebrae, and anteriorly by the intervertebral disc and adjacent vertebral bodies.


Anatomy_Gray

Anatomy_Gray. Each intervertebral foramen is a confined space surrounded by bone and ligament, and by joints. Pathology in any of these structures, and in the surrounding muscles, can affect structures within the foramen. In most regions of the vertebral column, the laminae and spinous processes of adjacent vertebrae overlap to form a 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 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 clinical procedures. 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).


Anatomy_Gray

Anatomy_Gray. 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 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.


Anatomy_Gray

Anatomy_Gray. 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. 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). The anulus fibrosus consists of an outer ring of collagen 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 intervertebral disc, is gelatinous, and absorbs compression forces between vertebrae.


Anatomy_Gray

Anatomy_Gray. The nucleus pulposus fills the center of the intervertebral disc, is gelatinous, and absorbs compression forces between vertebrae. Degenerative changes in the anulus fibrosus can lead to herniation of the nucleus pulposus. Posterolateral herniation can impinge on the roots of a spinal nerve in the intervertebral foramen. 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.


Anatomy_Gray

Anatomy_Gray. In cervical regions, the zygapophysial joints slope inferiorly 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 extension, 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. The lateral margins of the upper surfaces of typical cervical vertebrae are elevated into crests or lips termed uncinate processes. These may articulate with the body of the vertebra above to form small “uncovertebral” synovial joints (Fig. 2.33). Joints between vertebrae are reinforced and supported by numerous ligaments, which pass between vertebral bodies and interconnect components of the vertebral arches.


Anatomy_Gray

Anatomy_Gray. Joints between vertebrae are reinforced and supported by numerous ligaments, which pass between vertebral bodies and interconnect components of the vertebral arches. 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 intervertebral discs.


Anatomy_Gray

Anatomy_Gray. The posterior longitudinal ligament is on the posterior surfaces of the vertebral bodies and lines the anterior surface of the vertebral canal. Like the anterior longitudinal ligament, it is attached along its length to the vertebral bodies and intervertebral discs. The upper part of the posterior longitudinal ligament that connects CII to the intracranial aspect of the base of the skull is termed the tectorial membrane (see Fig. 2.20B). 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 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.


Anatomy_Gray

Anatomy_Gray. The supraspinous ligament connects and passes along the tips of the vertebral spinous processes from vertebra 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: 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. The ligamentum nuchae supports the head. It resists flexion and facilitates returning the head to the anatomical position. The broad lateral surfaces and the posterior edge of the ligament provide attachment for adjacent muscles.


Anatomy_Gray

Anatomy_Gray. 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 supraspinous ligament posteriorly and the ligamenta flava anteriorly on each side. Muscles of the back are organized into superficial, intermediate, 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: 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 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. Superficial group of back muscles


Anatomy_Gray

Anatomy_Gray. 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 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 trapezius muscle in the superior part of the back.


Anatomy_Gray

Anatomy_Gray. 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 of the scapula. Contraction of these fibers elevates the scapula. In addition, the superior and inferior fibers work 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.


Anatomy_Gray

Anatomy_Gray. The blood supply to the trapezius is from the superficial branch of the transverse cervical artery, the acromial branch of the suprascapular artery, and the dorsal branches of posterior intercostal arteries. 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 innervates 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.


Anatomy_Gray

Anatomy_Gray. 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 rotating 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. 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.


Anatomy_Gray

Anatomy_Gray. 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 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


Anatomy_Gray

Anatomy_Gray. 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.


Anatomy_Gray

Anatomy_Gray. 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 segmental branches of anterior rami of intercostal nerves. Their vascular supply is provided by a similar segmental pattern through the intercostal arteries. Deep group of back muscles


Anatomy_Gray

Anatomy_Gray. Deep group of back muscles 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: 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 intertransversarii. The vascular supply to this deep group of muscles is through branches of the vertebral, deep cervical, occipital, transverse cervical, posterior intercostal, subcostal, lumbar, and lateral sacral arteries. 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: Superiorly, it passes anteriorly to the serratus posterior muscle and is continuous with deep fascia in the neck.


Anatomy_Gray

Anatomy_Gray. 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 serratus posterior inferior muscles blend into the thoracolumbar fascia. In the lumbar region, the thoracolumbar fascia consists of three layers: 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 attachments, it extends laterally to cover the erector spinae.


Anatomy_Gray

Anatomy_Gray. The middle layer is attached medially to the tips of the transverse processes of the lumbar vertebrae and intertransverse ligaments—inferiorly, it is attached to the 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 abdominal wall) and is attached medially to the transverse 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. 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.


Anatomy_Gray

Anatomy_Gray. The two spinotransversales muscles run from the spinous processes and ligamentum nuchae upward and laterally (Fig. 2.49 and Table 2.3): 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 backward, extending the neck. Individually, each muscle rotates the head to one side—the same side as the contracting muscle.


Anatomy_Gray

Anatomy_Gray. Together the spinotransversales muscles draw the head backward, extending the neck. Individually, each muscle rotates the head to one side—the same side as the contracting muscle. 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, thoracis, cervicis, and capitis), depending on where the muscles attach superiorly.


Anatomy_Gray

Anatomy_Gray. 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 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.


Anatomy_Gray

Anatomy_Gray. The muscles in the erector spinae group are the primary extensors of the vertebral column and head. Acting bilaterally, 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 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 semispinalis, multifidus, and rotatores muscles.


Anatomy_Gray

Anatomy_Gray. The semispinalis muscles are the most superficial collection 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 processes and spanning between two and four vertebrae. The multifidus muscles are present throughout the length of the vertebral column but are best developed in the lumbar region.


Anatomy_Gray

Anatomy_Gray. The small rotatores muscles are the deepest of the transversospinales group. They are present throughout the length of the vertebral column but are best developed 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). 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.


Anatomy_Gray

Anatomy_Gray. One muscle in the transversospinales group, the semispinalis 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. The two groups of segmental muscles (Fig. 2.51 and Table 2.6) are deeply placed in the back and innervated by posterior rami of spinal nerves. The first group of segmental muscles are the levatores costarum muscles, which arise from the transverse 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.


Anatomy_Gray

Anatomy_Gray. The second group of segmental muscles are the true segmental muscles of the back—the interspinales, which pass between adjacent spinous processes, and the intertransversarii, which pass between adjacent transverse processes. These postural muscles stabilize adjoining vertebrae during movements of the vertebral column to allow more effective action of the large muscle groups. 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 suboccipital muscles (Figs. 2.51 and 2.52 and Table 2.7). They include, on each side: rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis inferior, and obliquus capitis superior.


Anatomy_Gray

Anatomy_Gray. Contraction of the suboccipital muscles extends and 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 atlas (Fig. 2.52). The vascular supply to the muscles in 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): 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. The contents of the suboccipital triangle include: posterior ramus of CI, vertebral artery, and veins


Anatomy_Gray

Anatomy_Gray. The obliquus capitis inferior muscle forms the inferior border. The contents of the suboccipital triangle include: posterior ramus of CI, vertebral artery, and veins 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 approximately to vertebra LIII but can reach as low as vertebra LIV. The distal end of the cord (the conus medullaris) is cone shaped. A fine filament of connective tissue (the pial part of the filum terminale) continues inferiorly from the apex of the conus medullaris.


Anatomy_Gray

Anatomy_Gray. 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 enlargement 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 associated with the origins of spinal nerves L1 to S3, which innervate the lower limbs. The external surface of the spinal cord is marked by a number of fissures and sulci (Fig. 2.54): The anterior median fissure extends the length of the anterior surface. The posterior median sulcus extends along the posterior surface. The posterolateral sulcus on each side of the posterior surface marks where the posterior rootlets of spinal nerves enter the cord. Internally, the cord has a small central canal surrounded by gray and white matter:


Anatomy_Gray

Anatomy_Gray. Internally, the cord has a small central canal surrounded by gray and white matter: 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 tracts that ascend and descend in the cord to other spinal cord levels or carry information to and from the brain.


Anatomy_Gray

Anatomy_Gray. The arterial supply to the spinal cord comes from two sources (Fig. 2.55). It consists of: 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 predominantly from the vertebral and deep cervical arteries in the neck, the posterior intercostal arteries in the thorax, and the lumbar arteries in the abdomen.


Anatomy_Gray

Anatomy_Gray. After entering an intervertebral foramen, the segmental spinal arteries give rise to anterior and posterior radicular 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 segmental spinal arteries also give off segmental medullary arteries (Fig. 2.55). These vessels pass directly to the longitudinally oriented vessels, reinforcing these.


Anatomy_Gray

Anatomy_Gray. 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 terminal branch of each vertebral artery (the posterior inferior 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.


Anatomy_Gray

Anatomy_Gray. The anterior and posterior spinal arteries are reinforced along their length by eight to ten segmental medullary arteries (Fig. 2.55). The largest of these is the arteria radicularis magna or the artery of Adamkiewicz (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. Veins that drain the spinal cord form a number of longitudinal channels (Fig. 2.56): Two pairs of veins on each side bracket the connections of the posterior and anterior roots to the cord. One midline channel parallels the anterior median fissure. One midline channel passes along the posterior median sulcus.


Anatomy_Gray

Anatomy_Gray. One midline channel parallels the anterior median fissure. One midline channel passes along the posterior median sulcus. These longitudinal channels drain into an extensive internal vertebral plexus in the extradural (epidural) space of the vertebral canal, which then drains into segmentally arranged vessels that connect with major systemic veins, such as the azygos system in the thorax. The internal vertebral plexus also communicates with intracranial veins.


Anatomy_Gray

Anatomy_Gray. The spinal dura mater is the outermost meningeal membrane 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.


Anatomy_Gray

Anatomy_Gray. 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. The arachnoid mater is a thin delicate membrane against, but not adherent to, the deep surface of the dura 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). 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).


Anatomy_Gray

Anatomy_Gray. 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 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 a consequence, CSF can be withdrawn from the subarachnoid space in the lower lumbar region without endangering the spinal cord.


Anatomy_Gray

Anatomy_Gray. 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 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). 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.


Anatomy_Gray

Anatomy_Gray. 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 generally occur between the exit points of adjacent posterior and anterior rootlets. The ligaments function to position the spinal cord in the center of the subarachnoid space. Arrangement of structures in the vertebral canal The vertebral canal is bordered: 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.


Anatomy_Gray

Anatomy_Gray. Between the walls of the vertebral canal and the dural 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 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. Each spinal nerve is connected to the spinal cord by posterior and anterior roots (Fig. 2.61):


Anatomy_Gray

Anatomy_Gray. Each spinal nerve is connected to the spinal cord by posterior and anterior roots (Fig. 2.61): 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. 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 rootlets, which attach to the spinal cord. 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 posterior and anterior roots on each side join to form a spinal nerve.


Anatomy_Gray

Anatomy_Gray. 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 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 of the skin, except for certain regions of the head. 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.


Anatomy_Gray

Anatomy_Gray. All major somatic plexuses (cervical, brachial, lumbar, and sacral) are formed by anterior rami. Because the spinal cord is much shorter than the vertebral 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 approximately 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. Nomenclature of spinal nerves


Anatomy_Gray

Anatomy_Gray. 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. The first cervical nerve (C1) emerges from the vertebral canal between the skull and vertebra CI (Fig. 2.63). Therefore 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 vertebrae CVII and TI. As a consequence, all remaining spinal nerves, beginning with T1, emerge from the vertebral canal below their respective vertebrae.


Anatomy_Gray

Anatomy_Gray. 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). 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.


Anatomy_Gray

Anatomy_Gray. A number of readily palpable bony features provide useful landmarks for defining muscles and for locating structures associated with the vertebral column. Among these features 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. How to identify specific vertebral


Anatomy_Gray

Anatomy_Gray. How to identify specific vertebral 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 protuberance 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. The spinous process of CVII is usually visible as a prominent 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 protuberance of the skull is the ligamentum nuchae, which is readily apparent as a longitudinal ridge when the neck is flexed (Fig. 2.67C).


Anatomy_Gray

Anatomy_Gray. Extending between CVII and the external occipital protuberance 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).


Anatomy_Gray

Anatomy_Gray. 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 posterior superior iliac spine are level with the SII vertebral spinous process (Fig. 2.67A). The tip of the coccyx is palpable at the base of the vertebral column between the gluteal masses (Fig. 2.67A).


Anatomy_Gray

Anatomy_Gray. The tip of the coccyx is palpable at the base of the vertebral 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


Anatomy_Gray

Anatomy_Gray. 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).


Anatomy_Gray

Anatomy_Gray. 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.


Anatomy_Gray

Anatomy_Gray. 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 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. 2.1 Skeletal framework of the back. Fig. 2.2 Curvatures of the vertebral column. Cervical curvature(secondary curvature)Thoracic curvature(primary curvature)Lumbar curvature(secondary curvature)Sacral/coccygeal curvature(primary curvature)Gravity lineConcave primarycurvature of backEarly embryoAdultSomites Fig. 2.3 Back movements. Fig. 2.4 Nervous system. Fig. 2.5 Vertebrae. Fig. 2.6 A typical vertebra. A. Superior view. B. Lateral view. Fig. 2.7 Back muscles. A. Extrinsic muscles. B. Intrinsic muscles.


Anatomy_Gray

Anatomy_Gray. Fig. 2.4 Nervous system. Fig. 2.5 Vertebrae. Fig. 2.6 A typical vertebra. A. Superior view. B. Lateral view. Fig. 2.7 Back muscles. A. Extrinsic muscles. B. Intrinsic muscles. Deep groupSerratus posteriorinferiorSerratus posteriorsuperiorSuboccipitalLevator scapulaeSpleniusRhomboid minorSuperficial groupABIntermediate groupIntrinsic musclesTrue back muscles innervated by posterior rami of spinal nervesRhomboid majorSpinalisIliocostalisErector spinaeLongissimusLatissimusdorsiTrapeziusExtrinsic musclesInnervated by anterior rami of spinal nerves or cranial nerve XI (trapezius) Fig. 2.8 Vertebral canal. Spinal cordPia materSubarachnoid spaceDura materArachnoid materAnterior ramusPosterior ramusPosition of spinal ganglionTransverseprocessSpinousprocessPosterior longitudinalligamentAnterior internal vertebralvenous plexusIntervertebral discExtradural spaceExtradural fatVertebral body Fig. 2.9 Spinal nerves (transverse section). Fig. 2.10 Relationships of the back to other regions.


Anatomy_Gray

Anatomy_Gray. Fig. 2.9 Spinal nerves (transverse section). Fig. 2.10 Relationships of the back to other regions. Cervical region• supports and moves head• transmits spinal cord and vertebral arteries between head and neck Thoracic region• support for thoraxLumbar region• support for abdomenSacral region• transmits weight to lower limbs through pelvic bones• framework for posterior aspect of pelvisVertebral arteries travelin transverse processes ofC6-C1, then pass throughforamen magnum Fig. 2.11 Vertebral canal, spinal cord, and spinal nerves. 1121110112233445595678412345678123C8T1T2T3T4T5T6T7T8T9T10T11T12L1L2L3L4L5S1S2S3S4S5CoC7C6C5C4Cervicalenlargement(of spinal cord)C2C3C1SubarachnoidspaceLumbosacralenlargement(of spinal cord)Arachnoid materEnd of spinalcord at LI–LIIvertebraeEnd ofsubarachnoidspace–sacralvertebra IIDura materPedicles ofvertebraeSpinalganglion Fig. 2.12 Intervertebral foramina. Fig. 2.13 Dermatomes innervated by posterior rami of spinal nerves.


Anatomy_Gray

Anatomy_Gray. Fig. 2.12 Intervertebral foramina. Fig. 2.13 Dermatomes innervated by posterior rami of spinal nerves. C2C3C4T2T3T4T5T6T7T8T9L5S1S2S4S3S5, Co*The dorsal rami of L4 and L5 may not have cutaneousbranches and may therefore not be represented asdermatomes on the backL4L3L2L1T11T12T10 Fig. 2.14 Vertebrae. Fig. 2.15 Radiograph of cervical region of vertebral column. A. Anteroposterior view. B. Lateral view. ARib IICIISpinous process of CVII Vertebralbody of CIIILocation ofintervertebral discVertebra prominens(spinous process of CVII)Posterior tubercleof CI (atlas)B Fig. 2.16 Radiograph of thoracic region of vertebral column. A. Anteroposterior view. B. Lateral view. RibPedicleLocation of intervertebral discSpinous processTransverse processVertebral bodyA BIntervertebral foramenVertebral bodyLocation of intervertebral disc Fig. 2.17 Radiograph of lumbar region of vertebral column. A. Anteroposterior view. B. Lateral view. RibTransverse processPedicleSpinous process of LIVA


Anatomy_Gray

Anatomy_Gray. Fig. 2.17 Radiograph of lumbar region of vertebral column. A. Anteroposterior view. B. Lateral view. RibTransverse processPedicleSpinous process of LIVA Location ofintervertebral discVertebral body of LIIIIntervertebral foramenB Fig. 2.18 Development of the vertebrae. Fig. 2.19 Typical vertebra. Fig. 2.20 Regional vertebrae. A. Typical cervical vertebra. B. Atlas and axis. C. Typical thoracic vertebra. D. Typical lumbar vertebra. E. Sacrum. F. Coccyx.


Anatomy_Gray

Anatomy_Gray. E. Sacrum. F. Coccyx. Transverse processDensDensForamen transversariumSuperior viewSuperior viewSuperior viewPosterior viewPosterosuperior viewBAnterior tuberclePosterior tubercleAnterior archLateral massPosterior archFacet for densFacet for occipital condyleImpressionsfor alarligamentsAlarligamentsTectorial membrane (upper partof posterior longitudinal ligament)PosteriorlongitudinalligamentFacets forattachment ofalar ligamentsAtlas (CI vertebra)Atlas (CI vertebra) and Axis (CII vertebra)Atlas (CIvertebra)and Axis(CII vertebra)and baseof skullAxis (CII vertebra)Transverse ligament of atlasTransverse ligament of atlasVertebral bodyTransverse processTransverseprocessSpinousprocessMammillaryprocessSpinousprocessSuperior viewLateral viewSuperior viewFacet for articulationwith tubercle ofits own ribDemifacet for articulationwith head of rib belowDemifacet for articulationwith head of its own ribCDApical ligamentof densInferior longitudinalband of cruciformligament


Anatomy_Gray

Anatomy_Gray. Anterior viewDorsolateral viewPosterior viewFacet for articulation with pelvic boneEFAnterior sacral foraminaPosterior sacral foraminaCoccygeal cornuIncomplete sacral canal Fig. 2.21 Radiograph showing CI (atlas) and CII (axis) vertebrae. Open mouth, anteroposterior (odontoid peg) view. Superior articularfacet of CIIDensInferior articular faceton lateral mass of CI Fig. 2.22 Intervertebral foramen. Fig. 2.23 Spaces between adjacent vertebral arches in the lumbar region. 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. 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.


Anatomy_Gray

Anatomy_Gray. 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. 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. Fig. 2.27 Severe scoliosis. A. Radiograph, anteroposterior view. B. Volume-rendered CT, anterior view. Fig. 2.28 Sagittal CT showing kyphosis. 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. Fused bodies of cervical vertebraeA HemivertebraPartial lumbarization of first sacral vertebraB


Anatomy_Gray

Anatomy_Gray. Fused bodies of cervical vertebraeA HemivertebraPartial lumbarization of first sacral vertebraB 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. Fig. 2.31 Intervertebral joints. Anulus fibrosusNucleus pulposusLayer of hyalinecartilage Fig. 2.32 Zygapophysial joints. Fig. 2.33 Uncovertebral joint. Fig. 2.34 Disc protrusion. T2-weighted magnetic resonance images of the lumbar region of the vertebral column. A. Sagittal plane. B. Axial plane. Fig. 2.35 Anterior and posterior longitudinal ligaments of vertebral column. Fig. 2.36 Ligamenta flava. Fig. 2.37 Supraspinous ligament and ligamentum nuchae. Fig. 2.38 Interspinous ligaments. Fig. 2.39 Axial slice MRI through the lumbar spine demonstrating bilateral hypertrophy of the ligamentum flavum.


Anatomy_Gray

Anatomy_Gray. Fig. 2.38 Interspinous ligaments. Fig. 2.39 Axial slice MRI through the lumbar spine demonstrating bilateral hypertrophy of the ligamentum flavum. 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. Fig. 2.41 A. Anterior lumbar interbody fusion (ALIF). B. Posterior lumbar interbody fusion (PLIF). Fig. 2.42 Superficial group of back muscles—trapezius and latissimus dorsi.


Anatomy_Gray

Anatomy_Gray. Fig. 2.41 A. Anterior lumbar interbody fusion (ALIF). B. Posterior lumbar interbody fusion (PLIF). Fig. 2.42 Superficial group of back muscles—trapezius and latissimus dorsi. Spinous process of CVIIAcromionSpine of scapulaIliac crestGreater occipital nerve(posterior ramus of C2)Third occipital nerve(posterior ramus of C3)Medial branches of posterior ramiLateral branches of posterior ramiTrapeziusLatissimus dorsiThoracolumbar fascia 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. Fig. 2.44 Innervation and blood supply of trapezius. TrapeziusLatissimus dorsiRhomboid minorRhomboid majorLevator scapulaeAccessory nerve [XI]Superficial branch of transverse cervical artery Fig. 2.45 Rhomboid muscles and levator scapulae. Fig. 2.46 Innervation and blood supply of the rhomboid muscles.


Anatomy_Gray

Anatomy_Gray. Fig. 2.45 Rhomboid muscles and levator scapulae. Fig. 2.46 Innervation and blood supply of the rhomboid muscles. Dorsal scapular nerveTrapeziusLatissimus dorsiRhomboid minorRhomboid majorLevator scapulaeSuperficial branch of transverse cervical arteryDeep branch of transverse cervical artery Fig. 2.47 Intermediate group of back muscles—serratus posterior muscles. Fig. 2.48 Thoracolumbar fascia and the deep back muscles (transverse section). Fig. 2.49 Deep group of back muscles—spinotransversales muscles (splenius capitis and splenius cervicis). Fig. 2.50 Deep group of back muscles—erector spinae muscles. Spinous process of CVIIIliac crestSplenius capitisLongissimus capitis Ligamentum nuchaeLongissimus thoracisLongissimus cervicisSpinalis thoracisSpinalisIliocostalis lumborum Iliocostalis thoracisIliocostalis cervicisIliocostalisLongissimus Fig. 2.51 Deep group of back muscles—transversospinales and segmental muscles.


Anatomy_Gray

Anatomy_Gray. Fig. 2.51 Deep group of back muscles—transversospinales and segmental muscles. Spinous process of CVIIObliquus capitis inferiorObliquus capitis superiorRectus capitis posterior minorRectus capitis posterior majorSemispinalis thoracisIntertransversariusErector spinaeRotatores thoracis(short, long)Levatores costarum(short, long)Semispinalis capitisMultifidus Fig. 2.52 Deep group of back muscles—suboccipital muscles. This also shows the borders of the suboccipital triangle. Spinous process of CIIPosterior ramus of C1Obliquus capitis superior Rectus capitis posterior minorObliquus capitis inferiorRectus capitis posterior majorSplenius capitisSplenius capitisLongissimus capitisSemispinalis cervicisSemispinalis capitisSemispinalis capitisVertebral artery Fig. 2.53 Spinal cord.


Anatomy_Gray

Anatomy_Gray. Fig. 2.53 Spinal cord. End of spinalcord LI–LIIConus medullarisInferior part ofarachnoid materEnd of subarachnoidspace SIICervicalenlargement(of spinal cord)Lumbosacralenlargement(of spinal cord)FilumterminalePial partDural partPedicles ofvertebrae Fig. 2.54 Features of the spinal cord. Fig. 2.55 Arteries that supply the spinal cord. A. Anterior view of spinal cord (not all segmental spinal arteries are shown). B. Segmental supply of spinal cord. Posterior spinal arteryADeep cervical arteryCostocervical trunkThyrocervical trunkSubclavian arteryPosterior intercostalarterySegmentalspinal arteryArtery of Adamkiewicz(branch fromsegmentalspinal artery)Ascending cervicalarteryVertebral arterySegmental medullaryarteriesAnterior spinal arterySegmental medullaryarteries (branch fromsegmental spinalartery)Lateral sacral arterySegmentalspinal artery Fig. 2.56 Veins that drain the spinal cord.


Anatomy_Gray

Anatomy_Gray. Fig. 2.56 Veins that drain the spinal cord. 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. Fig. 2.58 CT at the level of CI demonstrates two breaks in the closed ring of the atlas following an axial-loading injury. Fig. 2.59 Meninges. Fig. 2.60 Arrangement of structures in the vertebral canal and the back (lumbar region). Crura of diaphragmAortaPsoasDuraQuadratus lumborumInternal vertebral plexus of veinsin extradural spaceErector spinae musclesLigamenta flavaSupraspinous ligamentInterspinous ligamentLumbar arteryVeinCauda equinaSkinVertebraIntervertebral discIntervertebral foramenLaminaPediclePosterior longitudinal ligament Fig. 2.61 Basic organization of a spinal nerve. Fig. 2.62 Course of spinal nerves in the vertebral canal.


Anatomy_Gray

Anatomy_Gray. Fig. 2.61 Basic organization of a spinal nerve. Fig. 2.62 Course of spinal nerves in the vertebral canal. 1121110112233445595678412345678123C8T1T2T3T4T5T6T7T8T9T10T11T12L1L2L3L4L5S1S2S3S4S5CoC7C6C5C4Cervical enlargement(of spinal cord)C2C3C1Lumbosacral enlargement(of spinal cord)Cauda equinaPedicles of vertebraeSpinal ganglion Fig. 2.63 Nomenclature of the spinal nerves. Nerve C1 emerges betweenskull and CI vertebraNerve C8 emerges inferior topedicle of CVII vertebraNerves C2 to C7 emergesuperior to pediclesNerves T1 to Co emergeinferior to pedicles oftheir respective vertebraeC2C1C3C4C5C6C7C8T1CICVIITIPedicleTransition innomenclatureof nervesT2 Fig. 2.64 Normal appearance of the back. A. In women. B. In men. Fig. 2.65 Normal curvatures of the vertebral column. Fig. 2.66 Back of a woman with major palpable bony landmarks indicated.


Anatomy_Gray

Anatomy_Gray. Fig. 2.64 Normal appearance of the back. A. In women. B. In men. Fig. 2.65 Normal curvatures of the vertebral column. Fig. 2.66 Back of a woman with major palpable bony landmarks indicated. Spine of scapulaInferior angle of scapulaMedial border of scapulaPosition of externaloccipital protuberancePosterior superior iliac spineIliac crest 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.


Anatomy_Gray

Anatomy_Gray. Tip of coccyxSII vertebral spinous processTXII vertebral spinous processTVII vertebral spinous processTIII vertebral spinous processTI vertebral spinous processRoot of spine of scapulaInferior angle of scapulaHighest point of iliac crestIliac crestSacral dimpleCVII vertebral spinous processCII vertebral spinous processPosition of externaloccipital protuberanceLIV vertebral spinous processA Fig. 2.68 Back with the ends of the spinal cord and subarachnoid space indicated. A. In a man. 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.


Anatomy_Gray

Anatomy_Gray. Tip of coccyxSII vertebral spinous processTXII vertebral spinous processInferior end of spinal cord(normally betweenLI and LII vertebra)Inferior end ofsubarachnoid spaceALIV vertebral spinous process LIV vertebral spinous processNeedleLV vertebral spinous processTip of coccyxB Fig. 2.69 Back muscles. A. In a man with latissimus dorsi, trapezius, and erector spinae muscles outlined. 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. Fig. 2.70 MRI of the lumbar spine reveals posterior herniation of the L2-3 disc resulting in compression of the cauda equina filaments. Table 2.1 Superficial (appendicular) group of back muscles Table 2.2 Intermediate (respiratory) group of back muscles Table 2.3 Spinotransversales muscles Table 2.4 Erector spinae group of back muscles


Anatomy_Gray

Anatomy_Gray. Table 2.2 Intermediate (respiratory) group of back muscles Table 2.3 Spinotransversales muscles Table 2.4 Erector spinae group of back muscles Table 2.5 Transversospinales group of back muscles Table 2.6 Segmental back muscles Table 2.7 Suboccipital group of back muscles In the clinic 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. 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.


Anatomy_Gray

Anatomy_Gray. 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. In the clinic 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.


Anatomy_Gray

Anatomy_Gray. 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 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. In the clinic