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Conceptual overview GENERAL DESCRIPTION The back consists of the posterior aspect of the body and provides the musculoskeletal axis of support for the trunk. Bony elements consist mainly of the vertebrae, although proximal elements of the ribs, superior aspects of the pelvic bones, and posterior bas...

Conceptual overview GENERAL DESCRIPTION The back consists of the posterior aspect of the body and provides the musculoskeletal axis of support for the trunk. Bony elements consist mainly of the vertebrae, although proximal elements of the ribs, superior aspects of the pelvic bones, and posterior basal regions of the skull contribute to the back's skeletal framework (Fig. 2.1). Associated muscles interconnect the vertebrae and ribs with each other and with the pelvis and skull. The back contains the spinal cord and proximal parts of the spinal nerves, which send and receive information to and from most of the body. Back FUNCTIONS Support The skeletal and muscular elements of the back support the body's weight, transmit forces through the pelvis to the lower limbs, carry and position the head, and brace and help maneuver the upper limbs. The verte bral column is positioned posteriorly in the body at the midline. When viewed laterally, it has a number of curva tures (Fig. 2.2): The primary curvature of the vertebral column is concave anteriorly, reflecting the original shape of the embryo, and is retained in the thoracic and sacral regions in adults. Secondary curvatures, which are concave posteriorly, form in the cervical and lumbar regions and bring the center of gravity into a vertical line, which allows the body's weight to be balanced on the vertebral column in a way that expends the least amount of muscular energy to maintain an upright bipedal stance. As stresses on the back increase from the cervical to lumbar regions, lower back problems are common. Movement 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 f lexion (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 addi tive 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. Early embryo Adult Somites Concave primary curvature of back Cervical curvature (secondary curvature) Thoracic curvature (primary curvature) Lumbar curvature (secondary curvature) Sacral/coccygeal curvature (primary curvature) Gravity line 52 Fig. 2.2 Curvatures of the vertebral column. Conceptual Overview Functions Extension Flexion Lateral flexion Rotation Fig. 2.3 Back movements. In the cervical region, the first two vertebrae and associ ated muscles are specifically modified to support and posi tion the head. The head flexes and extends, in the nodding motion, on vertebra CI, and rotation of the head occurs as vertebra CI moves on vertebra CII (Fig. 2.3). Protection of the nervous system The vertebral column and associated soft tissues of the back contain the spinal cord and proximal parts of the spinal nerves (Fig. 2.4). The more distal parts of the spinal nerves pass into all other regions of the body, including certain regions of the head. Brain Cranial nerve Spinal cord Spinal nerve 2 Fig. 2.4 Nervous system. 53 Back COMPONENT PARTS Bones The major bones of the back are the 33 vertebrae (Fig. 2.5). The number and specific characteristics of the verte brae vary depending on the body region with which they are associated. There are seven cervical, twelve thoracic, f ive lumbar, five sacral, and three to four coccygeal verte brae. The sacral vertebrae fuse into a single bony element, the sacrum. The coccygeal vertebrae are rudimentary in structure, vary in number from three to four, and often fuse into a single coccyx. 7 cervical vertebrae (CI--CVII) 12 thoracic vertebrae (TI--TXII) 5 lumbar vertebrae (LI--LV) Sacrum (5 fused sacral vertebrae I-V) Coccyx (3--4 fused coccygeal vertebrae I-IV) 54 Fig. 2.5 Vertebrae. Conceptual Overview Component Parts Typical vertebra A typical vertebra consists of a vertebral body and a verte bral arch (Fig. 2.6). The vertebral body is anterior and is the major weight bearing component of the bone. It increases in size from vertebra CII to vertebra LV. Fibrocartilaginous inter vertebral discs separate the vertebral bodies of adjacent vertebrae. The vertebral arch is firmly anchored to the posterior surface of the vertebral body by two pedicles, which form the lateral pillars of the vertebral arch. The roof of the vertebral arch is formed by right and left laminae, which fuse at the midline. The vertebral arches of the vertebrae are aligned to form the lateral and posterior walls of the vertebral canal, which extends from the first cervical vertebra (CI) to the last sacral vertebra (vertebra SV). This bony canal contains the spinal cord and its protective membranes, together with blood vessels, connective tissue, fat, and proximal parts of spinal nerves. The vertebral arch of a typical vertebra has a number of characteristic projections, which serve as: 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. Anterior Pedicle Transverse process Lamina Spinous process A Vertebral body 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 articu late with the vertebral bodies and transverse processes. In all other regions, these rib elements are small and are incorporated into the transverse processes. Occasionally, they develop into ribs in regions other than the thorax, usually in the lower cervical and upper lumbar regions. Muscles Muscles in the back can be classified as extrinsic or intrinsic based on their embryological origin and type of innerva tion (Fig. 2.7). The extrinsic muscles are involved with movements of the upper limbs and thoracic wall and, in general, are innervated by anterior rami of spinal nerves. The superfi cial group of these muscles is related to the upper limbs, while the intermediate layer of muscles is associated with 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. Superior Superior vertebral notch Pedicle Superior articular process Transverse process Spinous process Anterior Fused costal (rib) element Vertebral arch Posterior Vertebral body B Inferior Inferior vertebral notch Lamina Inferior articular process Posterior 2 Fig. 2.6 A typical vertebra. A. Superior view. B. Lateral view. 55 Back Trapezius Latissimus dorsi A Superficial group Erector spinae Levator scapulae Rhomboid minor Rhomboid major Serratus posterior inferior Extrinsic muscles Innervated by anterior rami of spinal nerves or cranial nerve XI (trapezius) Suboccipital Longissimus Iliocostalis Spinalis B Deep group Intrinsic muscles True back muscles innervated by posterior rami of spinal nerves Fig. 2.7 Back muscles. A. Extrinsic muscles. B. Intrinsic muscles. Serratus posterior superior Intermediate group Splenius 56 Conceptual Overview Component Parts Vertebral canal 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. 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): Anterior internal vertebral venous plexus Posterior longitudinal ligament Extradural space Extradural fat Vertebral body Intervertebral disc 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 sepa rated from the pia by the subarachnoid space, which contains cerebrospinal fluid. The thickest and most external of the membranes, the dura mater, lies directly against, but is not attached to, the arachnoid mater. In the vertebral canal, the dura mater is separated from surrounding bone by an extradural (epidural) space containing loose connective tissue, fat, and a venous plexus. Spinal cord Pia mater Subarachnoid space Arachnoid mater Dura mater Position of spinal ganglion Posterior ramus Anterior ramus Transverse process Spinous process 2 Fig. 2.8 Vertebral canal. 57 Back Spinal nerves The 31 pairs of spinal nerves are segmental in distribution and emerge from the vertebral canal between the pedicles of adjacent vertebrae. There are eight pairs of cervical nerves (C1 to C8), twelve thoracic (T1 to T12), five lumbar (L1 to L5), five sacral (S1 to S5), and one coccygeal (Co). 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: Prevertebral ganglion (sympathetic) Vertebral body Anterior root Visceral components Posterior root Lamina a posterior ramus---collectively, the small posterior rami innervate the back; and an anterior ramus---the much larger anterior rami innervate most other regions of the body except the head, which is innervated predominantly, but not exclu sively, by cranial nerves. The anterior rami form the major somatic plexuses (cervical, brachial, lumbar, and sacral) of the body. Major visceral components of the PNS (sympathetic trunk and prevertebral plexus) of the body are also associated mainly with the anterior rami of spinal nerves. Prevertebral plexus Aorta Sympathetic ganglion Anterior ramus Posterior ramus Spinal nerve Extradural space Spinal cord Spinous process Arachnoid mater Pia mater Dura mater Subarachnoid space 58 Fig. 2.9 Spinal nerves (transverse section). Conceptual Overview Relationship to Other Regions RELATIONSHIP TO OTHER REGIONS Head Cervical regions of the back constitute the skeletal and much of the muscular framework of the neck, which in turn supports and moves the head (Fig. 2.10). Vertebral arteries travel in transverse processes of C6-C1, then pass through foramen magnum The brain and cranial meninges are continuous with the spinal cord meninges at the foramen magnum of the skull. The paired vertebral arteries ascend, one on each side, through foramina in the transverse processes of cervi cal vertebrae and pass through the foramen magnum to participate, with the internal carotid arteries, in supplying blood to the brain. Cervical region supports and moves head transmits spinal cord and vertebral arteries between head and neck Thoracic region support for thorax Lumbar region support for abdomen Sacral region transmits weight to lower limbs through pelvic bones framework for posterior aspect of pelvis 2 Fig. 2.10 Relationships of the back to other regions. 59 Back Thorax, abdomen, and pelvis The different regions of the vertebral column contribute to the skeletal framework of the thorax, abdomen, and pelvis (Fig. 2.10). In addition to providing support for each of these parts of the body, the vertebrae provide attachments for muscles and fascia, and articulation sites for other bones. The anterior rami of spinal nerves associated with the thorax, abdomen, and pelvis pass into these parts of the body from the back. Limbs The bones of the back provide extensive attachments for muscles associated with anchoring and moving the upper limbs on the trunk. This is less true of the lower limbs, which are firmly anchored to the vertebral column through articulation of the pelvic bones with the sacrum. The upper and lower limbs are innervated by anterior rami of spinal nerves that emerge from cervical and lumbosacral levels, respectively, of the vertebral column. KEY FEATURES Long vertebral column and short spinal cord During development, the vertebral column grows much faster than the spinal cord. As a result, the spinal cord does not extend the entire length of the vertebral canal (Fig. 2.11). In the adult, the spinal cord typically ends between vertebrae LI and LII, although it can end as high as vertebra TXII and as low as the disc between vertebrae LII and LIII. Spinal nerves originate from the spinal cord at increas ingly oblique angles from vertebrae CI to Co, and the nerve roots pass in the vertebral canal for increasingly longer distances. Their spinal cord level of origin therefore becomes increasingly dissociated from their vertebral column level of exit. This is particularly evident for lumbar and sacral spinal nerves. 1 Subarachnoid space Cervical enlargement (of spinal cord) Pedicles of vertebrae Spinal ganglion Lumbosacral enlargement (of spinal cord) End of spinal cord at LI--LII vertebrae Arachnoid mater Dura mater End of subarachnoid space--sacral vertebra II 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 10 11 12 1 C1 C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 2 3 4 5 1 2 3 4 5 1 T11 T12 L1 L2 L3 L4 L5 S1 S2 S3 S4 S5 Co 60 Fig. 2.11 Vertebral canal, spinal cord, and spinal nerves. Conceptual Overview Key Features Intervertebral foramina and spinal nerves Each spinal nerve exits the vertebral canal laterally through an intervertebral foramen (Fig. 2.12). The foramen is formed between adjacent vertebral arches and is closely related to intervertebral joints: 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. Superior articular process Joint between superior and inferior articular processes (zygapophysial joint) Superior vertebral notch Intervertebral foramen Spinal nerve Intervertebral disc Inferior articular process Inferior vertebral notch Fig. 2.12 Intervertebral foramina. 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. C2 C3 C4 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L3 S5, Co L4 L5 S1 S2 S3 S4 \*The dorsal rami of L4 and L5 may not have cutaneous branches and may therefore not be represented as dermatomes on the back Fig. 2.13 Dermatomes innervated by posterior rami of spinal nerves. 2 61 Back Regional anatomy SKELETAL FRAMEWORK 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. Anterior Fused costal (rib) element Rib Fused costal (rib) element Cervical vertebra Thoracic vertebra Vertebrae There are approximately 33 vertebrae, which are subdi vided 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). Foramen transversarium Lumbar vertebra Posterior 7 Cervical vertebrae 12 Thoracic vertebrae 5 Lumbar vertebrae Sacrum Coccyx 62 Fig. 2.14 Vertebrae. Regional Anatomy Skeletal Framework 2 63 Fig. 2.15 Radiograph of cervical region of vertebral column. A. Anteroposterior view. B. Lateral view. A Rib II CII Spinous process of CVII Vertebral body of CIII Location of intervertebral disc Vertebra prominens (spinous process of CVII) Posterior tubercle of CI (atlas) B Back 64 Fig. 2.16 Radiograph of thoracic region of vertebral column. A. Anteroposterior view. B. Lateral view. Rib Pedicle Location of intervertebral disc Spinous process Transverse process Vertebral body A B Intervertebral foramen Vertebral body Location of intervertebral disc 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. Inferior to the thoracic vertebrae are five lumbar verte brae, which form the skeletal support for the posterior abdominal wall and are characterized by their large size (Figs. 2.14 and 2.17). Next are five sacral vertebrae fused into one single bone called the sacrum, which articulates on each side with a pelvic bone and is a component of the pelvic wall. Inferior to the sacrum is a variable number, usually four, of coccygeal vertebrae, which fuse into a single small triangular bone called the coccyx. In the embryo, the vertebrae are formed intersegmen tally from cells called sclerotomes, which originate from adjacent somites (Fig. 2.18). Each vertebra is derived from the cranial parts of the two somites below, one on each side, and the caudal parts of the two somites above. The Regional Anatomy Skeletal Framework 2 65 Fig. 2.17 Radiograph of lumbar region of vertebral column. A. Anteroposterior view. B. Lateral view. Rib Transverse process Pedicle Spinous process of LIV A Location of intervertebral disc Vertebral body of LIII Intervertebral foramen B Fig. 2.18 Development of the vertebrae. Migrating sclerotome cells Somites Developing spinal nerve Developing spinal nerve Somites Sclerotome Neural tube Forming vertebra Caudal Cranial Back spinal nerves develop segmentally and pass between the forming vertebrae. Typical vertebra A typical vertebra consists of a vertebral body and a poste rior vertebral arch (Fig. 2.19). Extending from the vertebral arch are a number of processes for muscle attachment and articulation with adjacent bone. The vertebral body is the weight-bearing part of the vertebra and is linked to adjacent vertebral bodies by intervertebral discs and ligaments. The size of vertebral bodies increases inferiorly as the amount of weight sup ported increases. The vertebral arch forms the lateral and posterior parts of the vertebral foramen. The vertebral foramina of all the vertebrae together form the vertebral canal, which contains and protects the spinal cord. Superiorly, the vertebral canal is continu ous, through the foramen magnum of the skull, with the cranial cavity of the head. Vertebral body Pedicle Transverse process Lamina The vertebral arch of each vertebra consists of pedicles and laminae (Fig. 2.19): The two pedicles are bony pillars that attach the verte bral arch to the vertebral body. The two laminae are flat sheets of bone that extend from each pedicle to meet in the midline and form the roof of the vertebral arch. A spinous process projects posteriorly and inferiorly from the junction of the two laminae and is a site for muscle and ligament attachment. A transverse process extends posterolaterally from the junction of the pedicle and lamina on each side and is a site for muscle and ligament attachment, and for articu lation with ribs in the thoracic region. Also projecting from the region where the pedicles join the laminae are superior and inferior articular processes (Fig. 2.19), which articulate with the inferior and superior articular processes, respectively, of adjacent vertebrae. Superior articular process Superior vertebral notch Vertebral arch Spinous process Fig. 2.19 Typical vertebra. Superior view Inferior articular process Inferior vertebral notch Superolateral oblique view 66 Regional Anatomy Skeletal Framework 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 ver tebral notches participate in forming intervertebral foramina. Cervical vertebrae The seven cervical vertebrae are characterized by their small size and by the presence of a foramen in each trans verse process. A typical cervical vertebra has the following features (Fig. 2.20A): Superior view Foramen transversarium Vertebral canal Vertebral body 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. Anterior view Uncinate process Transverse process A Spinous process Fig. 2.20 Regional vertebrae. A. Typical cervical vertebra. Foramen transversarium Spinous process Continued 2 67 Back Facet for dens Posterior arch Dens B Transverse process Atlas (CI vertebra) Anterior tubercle Impressions for alar ligaments Superior view Superior view Posterior tubercle Atlas (CI vertebra) and Axis (CII vertebra) Transverse ligament of atlas Anterior arch Lateral mass Transverse process Foramen transversarium Facet for occipital condyle Tectorial membrane (upper part of posterior longitudinal ligament) Transverse ligament of atlas Axis (CII vertebra) Inferior longitudinal band of cruciform ligament Dens Facets for attachment of alar ligaments Superior view Apical ligament of dens Atlas (CI vertebra) and Axis (CII vertebra) and base of skull Alar ligaments Posterior longitudinal ligament Posterior view Demifacet for articulation with head of its own rib Demifacet for articulation with head of rib below Spinous process C Superior view Lateral view Posterosuperior view Vertebral body Facet for articulation with tubercle of its own rib Transverse process D Mammillary process Spinous process Superior view 68 Fig. 2.20, cont'd B. Atlas and axis. C. Typical thoracic vertebra. D. Typical lumbar vertebra. Regional Anatomy Skeletal Framework Posterior sacral foramina Anterior sacral foramina E Anterior view Fig. 2.20, cont'd E. Sacrum. F. Coccyx. Facet for articulation with pelvic bone Dorsolateral view Incomplete sacral canal Coccygeal cornu F Posterior view Atlas and axis Vertebra CI (the atlas) articulates with the head (Fig. 2.21). Its major distinguishing feature is that it lacks a vertebral body (Fig. 2.20B). In fact, the vertebral body of CI fuses onto the body of CII during development to become the dens of CII. As a result, there is no intervertebral disc Inferior articular facet on lateral mass of CI Superior articular facet of CII Dens Fig. 2.21 Radiograph showing CI (atlas) and CII (axis) vertebrae. Open mouth, anteroposterior (odontoid peg) view. between CI and CII. When viewed from above, the atlas is ring shaped and composed of two lateral masses inter connected by an anterior arch and a posterior arch. Each lateral mass articulates above with an occipital condyle of the skull and below with the superior articular process of vertebra CII (the axis). The superior articular surfaces are bean shaped and concave, whereas the infe rior articular surfaces are almost circular and flat. The atlanto-occipital joint allows the head to nod up and down on the vertebral column. The posterior surface of the anterior arch has an articu lar facet for the dens, which projects superiorly from the vertebral body of the axis. The dens is held in position by a strong transverse ligament of atlas posterior to it and spanning the distance between the oval attachment facets on the medial surfaces of the lateral masses of the atlas. The dens acts as a pivot that allows the atlas and attached head to rotate on the axis, side to side. The transverse processes of the atlas are large and protrude further laterally than those of the other cervical vertebrae and act as levers for muscle action, particularly for muscles that move the head at the atlanto-axial joints. The axis is characterized by the large tooth-like dens, which extends superiorly from the vertebral body (Figs. 2.20B and 2.21). The anterior surface of the dens has an oval facet for articulation with the anterior arch of the atlas. The two superolateral surfaces of the dens possess cir cular impressions that serve as attachment sites for strong 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. 2 69 Back Thoracic vertebrae The twelve thoracic vertebrae are all characterized by their articulation with ribs. A typical thoracic vertebra has two partial facets (superior and inferior costal facets) on each side of the vertebral body for articulation with the head of its own rib and the head of the rib below (Fig. 2.20C). The superior costal facet is much larger than the inferior costal facet. Each transverse process also has a facet (transverse costal facet) for articulation with the tubercle of its own rib. The vertebral body of the vertebra is somewhat heart shaped when viewed from above, and the vertebral foramen is circular. Lumbar vertebrae The five lumbar vertebrae are distinguished from vertebrae in other regions by their large size (Fig. 2.20D). Also, they lack facets for articulation with ribs. The transverse proc esses are generally thin and long, with the exception of those on vertebra LV, which are massive and somewhat cone shaped for the attachment of iliolumbar ligaments to connect the transverse processes to the pelvic bones. The vertebral body of a typical lumbar vertebra is cylin drical and the vertebral foramen is triangular in shape and larger than in the thoracic vertebrae. Sacrum The sacrum is a single bone that represents the five fused sacral vertebrae (Fig. 2.20E). It is triangular in shape with the apex pointed inferiorly, and is curved so that it has a concave anterior surface and a correspondingly convex posterior surface. It articulates above with vertebra LV Inferior vertebral notch Zygapophysial joint and below with the coccyx. It has two large L-shaped facets, one on each lateral surface, for articulation with the pelvic bones. The posterior surface of the sacrum has four pairs of posterior sacral foramina, and the anterior surface has four pairs of anterior sacral foramina for the passage of the posterior and anterior rami, respectively, of S1 to S4 spinal nerves. The posterior wall of the vertebral canal may be incom plete near the inferior end of the sacrum. Coccyx The coccyx is a small triangular bone that articulates with the inferior end of the sacrum and represents three to four fused coccygeal vertebrae (Fig. 2.20F). It is characterized by its small size and by the absence of vertebral arches and therefore a vertebral canal. Intervertebral foramina Intervertebral foramina are formed on each side between adjacent parts of vertebrae and associated intervertebral discs (Fig. 2.22). The foramina allow structures, such as spinal nerves and blood vessels, to pass in and out of the vertebral canal. An intervertebral foramen is formed by the inferior vertebral notch on the pedicle of the vertebra above and the superior vertebral notch on the pedicle of the vertebra below. The foramen is bordered: posteriorly by the zygapophysial joint between the articular processes of the two vertebrae, and Superior vertebral notch Intervertebral foramen Intervertebral disc 70 Fig. 2.22 Intervertebral foramen. Regional Anatomy Skeletal Framework anteriorly by the intervertebral disc and adjacent verte bral bodies. Each intervertebral foramen is a confined space sur rounded by bone and ligament, and by joints. Pathology in any of these structures, and in the surrounding muscles, can affect structures within the foramen. Posterior spaces between vertebral arches In most regions of the vertebral column, the laminae and spinous processes of adjacent vertebrae overlap to form a 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 clini cal procedures. Thoracic vertebrae Lumbar vertebrae Fig. 2.23 Spaces between adjacent vertebral arches in the lumbar region. Lamina Spinous process Spinous process Lamina Space between adjacent laminae 2 71 Back 72 In the clinic Spina bifida Spina bifida is a disorder in which the two sides of vertebral arches, usually in lower vertebrae, fail to fuse during development, resulting in an "open" vertebral canal (Fig. 2.24). There are two types of spina bifida. The commonest type is spina bifida occulta, in which there is a defect in the vertebral arch of LV or SI. This defect occurs in as many as 10% of individuals and results in failure of the posterior arch to fuse in the midline. Clinically, the patient is asymptomatic, although physical examination may reveal a tuft of hair over the spinous processes. The more severe form of spina bifida involves complete failure of fusion of the posterior arch at the lumbosacral junction, with a large outpouching of the meninges. This may contain cerebrospinal fluid (a meningocele) or a portion of the spinal cord (a myelomeningocele). These abnormalities may result in a variety of neurological deficits, including problems with walking and bladder function. 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. Spinal cord Myelomeningocele Vertebral spinous process Brain Fourth ventricle Thoracic aorta Vertebral body Regional Anatomy Skeletal Framework In the clinic Vertebroplasty Vertebroplasty is a relatively new technique in which the body of a vertebra can be filled with bone cement (typically methyl methacrylate). The indications for the technique include vertebral body collapse and pain from the vertebral body, which may be secondary to tumor infiltration. The procedure is most commonly performed for osteoporotic wedge fractures, which are a considerable cause of morbidity and pain in older patients. Osteoporotic wedge fractures (Fig. 2.25) typically occur in the thoracolumbar region, and the approach to performing vertebroplasty is novel and relatively straightforward. The procedure is performed under sedation or light general Wedge fracture Fig. 2.25 Radiograph of the lumbar region of the vertebral column demonstrating a wedge fracture of the L1 vertebra. This condition is typically seen in patients with osteoporosis. anesthetic. Using X-ray guidance the pedicle is identified on the anteroposterior image. A metal cannula is placed through the pedicle into the vertebral body. Liquid bone cement is injected via the cannula into the vertebral body (Fig. 2.26). The function of the bone cement is two-fold. First, it increases the strength of the vertebral body and prevents further loss of height. Furthermore, as the bone cement sets, there is a degree of heat generated that is believed to disrupt pain nerve endings. Kyphoplasty is a similar technique that aims to restore some or all of the lost vertebral body height from the wedge fracture by injecting liquid bone cement into the vertebral body. Fig. 2.26 Radiograph of the lumbar region of the vertebral column demonstrating three intrapedicular needles, all of which have been placed into the middle of the vertebral bodies. The high-density material is radiopaque bone cement, which has been injected as a liquid that will harden. 2 73 Back 74 In the clinic Scoliosis Scoliosis is an abnormal lateral curvature of the vertebral column (Fig. 2.27). A true scoliosis involves not only the curvature (right- or left-sided) but also a rotational element of one vertebra upon another. The commonest types of scoliosis are those for which we have little understanding about how or why they occur and are termed idiopathic scoliosis. It is thought that there is some initial axial rotation of the vertebrae, which then alters the locations of the mechanical compressive and distractive forces applied through the vertebral growth plates, leading to changes in speed of bone growth and ultimately changes to spinal curvature. These are never present at birth and tend to occur in either the infantile, juvenile, or adolescent age groups. The vertebral bodies and posterior elements (pedicles and laminae) are normal in these patients. When a scoliosis is present from birth (congenital scoliosis) it is usually associated with other developmental abnormalities. In these patients, there is a strong association with other abnormalities of the chest wall, genitourinary tract, and heart disease. This group of patients needs careful evaluation by many specialists. A rare but important group of scoliosis is that in which the muscle is abnormal. Muscular dystrophy is the commonest example. The abnormal muscle does not retain the normal alignment of the vertebral column, and curvature develops as a result. A muscle biopsy is needed to make the diagnosis. Other disorders that can produce scoliosis include bone tumors, spinal cord tumors, and localized disc protrusions. A Fig. 2.27 Severe scoliosis. A. Radiograph, anteroposterior view. B. Volume-rendered CT, anterior view. B Regional Anatomy Skeletal Framework 2 75 In the clinic Lordosis Lordosis is abnormal curvature of the vertebral column in the lumbar region, producing a swayback deformity. In the clinic Kyphosis Kyphosis is abnormal curvature of the vertebral column in the thoracic region, producing a "hunchback" deformity. This condition occurs in certain disease states, the most dramatic of which is usually secondary to tuberculosis infection of a thoracic vertebral body, where the kyphosis becomes angulated at the site of the lesion. This produces the gibbus deformity, a deformity that was prevalent before the use of antituberculous medication (Fig. 2.28). Fig. 2.28 Sagittal CT showing kyphosis. Back In the clinic Variation in vertebral numbers There are usually seven cervical vertebrae, although in certain diseases these may be fused. Fusion of cervical vertebrae (Fig. 2.29A) can be associated with other abnormalities, for example Klippel-Feil syndrome, in which there is fusion of vertebrae CI and CII or CV and CVI, and may be associated with a high-riding scapula (Sprengel's shoulder) and cardiac abnormalities. Variations in the number of thoracic vertebrae also are well described. A Fused bodies of cervical vertebrae C One of the commonest abnormalities in the lumbar vertebrae is a partial fusion of vertebra LV with the sacrum (sacralization of the lumbar vertebra). Partial separation of vertebra SI from the sacrum (lumbarization of first sacral vertebra) may also occur (Fig. 2.29B). The LV vertebra can usually be identified by the iliolumbar ligament, which is a band of connective tissue that runs from the tip of the transverse process of LV to the iliac crest bilaterally (Fig. 2.29C). A hemivertebra occurs when a vertebra develops only on one side (Fig. 2.29B). Hemivertebra Iliolumbar ligament B Partial lumbarization of first sacral vertebra Fig. 2.29 Variations in vertebral number. A. Fused vertebral bodies of cervical vertebrae. B. Hemivertebra. C. Axial slice MRI through the LV vertebra. The iliolumbar ligament runs from the tip of the LV vertebra transverse process to the iliac crest. 76 Regional Anatomy Skeletal Framework 2 77 In the clinic The vertebrae and cancer The vertebrae are common sites for metastatic disease (secondary spread of cancer cells). When cancer cells grow within the vertebral bodies and the posterior elements, they interrupt normal bone cell turnover, leading to either bone destruction or formation and destroying the mechanical properties of the bone. A minor injury may therefore lead to vertebral collapse (Fig. 2.30A). Cancer cells have a much higher glucose metabolism compared with normal adjacent bone cells. These metastatic cancer cells can therefore be detected by administering radioisotope-labeled glucose to a patient and then tracing where the labeled glucose has been metabolized (Fig. 2.30B). Importantly, vertebrae that contain extensive metastatic disease may extrude fragments of tumor into the vertebral canal, compressing nerves and the spinal cord. A B2 B1 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. Back In the clinic Osteoporosis Osteoporosis is a pathophysiologic condition in which bone quality is normal but the quantity of bone is deficient. It is a metabolic bone disorder that commonly occurs in women in their 50s and 60s and in men in their 70s. Many factors influence the development of osteoporosis, including genetic predetermination, level of activity and nutritional status, and, in particular, estrogen levels in women. Typical complications of osteoporosis include "crush" vertebral body fractures, distal fractures of the radius, and hip fractures. JOINTS Joints between vertebrae in the back The two major types of joints between vertebrae are: symphyses between vertebral bodies (Fig. 2.31), and synovial joints between articular processes (Fig. 2.32). A typical vertebra has a total of six joints with adjacent vertebrae: four synovial joints (two above and two below) and two symphyses (one above and one below). Each symphysis includes an intervertebral disc. Although the movement between any two vertebrae is limited, the summation of movement among all vertebrae 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. With increasing age and poor-quality bone, patients are more susceptible to fracture. Healing tends to be impaired in these elderly patients, who consequently require long hospital stays and prolonged rehabilitation. Patients likely to develop osteoporosis can be identified by dual-photon X-ray absorptiometry (DXA) scanning. Low-dose X-rays are passed through the bone, and by counting the number of photons detected and knowing the dose given, the number of X-rays absorbed by the bone can be calculated. The amount of X-ray absorption can be directly correlated with the bone mass, and this can be used to predict whether a patient is at risk for osteoporotic fractures. Anulus fibrosus Nucleus pulposus Fig. 2.31 Intervertebral joints. Layer of hyaline cartilage 78 Regional Anatomy Joints 2 79 Fig. 2.32 Zygapophysial joints. Zygapophysial joint Zygapophysial joint Zygapophysial joint "Sloped from anterior to posterior" "Vertical" "Wrapped" Cervical Thoracic Lumbar Superior view Lateral view Lateral view Lateral view Symphyses between vertebral bodies (intervertebral discs) The symphysis between adjacent vertebral bodies is formed by a layer of hyaline cartilage on each vertebral body and an intervertebral disc, which lies between the layers. The intervertebral disc consists of an outer anulus fibrosus, which surrounds a central nucleus pulposus (Fig. 2.31). The anulus fibrosus consists of an outer ring of col lagen surrounding a wider zone of fibrocartilage arranged in a lamellar configuration. This arrangement of fibers limits rotation between vertebrae. The nucleus pulposus fills the center of the interver tebral disc, is gelatinous, and absorbs compression forces between vertebrae. Degenerative changes in the anulus fibrosus can lead to herniation of the nucleus pulposus. Posterolateral hernia tion can impinge on the roots of a spinal nerve in the intervertebral foramen. Joints between vertebral arches (zygapophysial joints) The synovial joints between superior and inferior articular processes on adjacent vertebrae are the zygapophysial joints (Fig. 2.32). A thin articular capsule attached to the margins of the articular facets encloses each joint. In cervical regions, the zygapophysial joints slope infe riorly from anterior to posterior and their shape facilitates flexion and extension. In thoracic regions, the joints are oriented vertically and their shape limits flexion and exten sion, but facilitates rotation. In lumbar regions, the joint surfaces are curved and adjacent processes interlock, thereby limiting range of movement, though flexion and extension are still major movements in the lumbar region. "Uncovertebral" joints The lateral margins of the upper surfaces of typical cervi cal vertebrae are elevated into crests or lips termed uncinate processes. These may articulate with the body of the ver tebra above to form small "uncovertebral" synovial joints (Fig. 2.33). Back 80 Fig. 2.33 Uncovertebral joint. CIV CV Uncovertebral joint Uncinate process In the clinic Back pain Back pain is an extremely common disorder. It can be related to mechanical problems or to disc protrusion impinging on a nerve. In cases involving discs, it may be necessary to operate and remove the disc that is pressing on the nerve. Not infrequently, patients complain of pain and no immediate cause is found; the pain is therefore attributed to mechanical discomfort, which may be caused by degenerative disease. One of the treatments is to pass a needle into the facet joint and inject it with local anesthetic and corticosteroid. In the clinic Herniation of intervertebral discs The discs between the vertebrae are made up of a central portion (the nucleus pulposus) and a complex series of fibrous rings (anulus fibrosus). A tear can occur within the anulus fibrosus through which the material of the nucleus pulposus can track. After a period of time, this material may track into the vertebral canal or into the intervertebral foramen to impinge on neural structures (Fig. 2.34). This is a common cause of back pain. A disc may protrude posteriorly to directly impinge on the cord or the roots of the lumbar nerves, depending on the level, or may protrude posterolaterally adjacent to the pedicle and impinge on the descending root. In cervical regions of the vertebral column, cervical disc protrusions often become ossified and are termed disc osteophyte bars. Fig. 2.34 Disc protrusion. T2-weighted magnetic resonance images of the lumbar region of the vertebral column. A. Sagittal plane. B. Axial plane. LIV vertebra Disc protrusion Vertebral canal containing CSF and cauda equina A Disc protrusion Meningeal sac containing CSF and cauda equina Facet Psoas B Regional Anatomy Ligaments 2 81 LIGAMENTS Joints between vertebrae are reinforced and supported by numerous ligaments, which pass between vertebral bodies and interconnect components of the vertebral arches. Anterior and posterior longitudinal ligaments The anterior and posterior longitudinal ligaments are on the anterior and posterior surfaces of the vertebral bodies and extend along most of the vertebral column (Fig. 2.35). The anterior longitudinal ligament is attached superiorly to the base of the skull and extends inferiorly to attach to the anterior surface of the sacrum. Along its length it is attached to the vertebral bodies and interverte bral discs. The posterior longitudinal ligament is on the poste rior surfaces of the vertebral bodies and lines the anterior surface of the vertebral canal. Like the anterior longitudi nal ligament, it is attached along its length to the vertebral bodies and intervertebral discs. The upper part of the pos terior longitudinal ligament that connects CII to the intra cranial aspect of the base of the skull is termed the tectorial membrane (see Fig. 2.20B). Ligamenta flava The ligamenta flava, on each side, pass between the laminae of adjacent vertebrae (Fig. 2.36). These thin, broad ligaments consist predominantly of elastic tissue and form part of the posterior surface of the vertebral In the clinic Joint diseases Some diseases have a predilection for synovial joints rather than symphyses. A typical example is rheumatoid arthritis, which primarily affects synovial joints and synovial bursae, resulting in destruction of the joint and