Medical School · Year 1 · Anatomy Msk · includes a quiz and discussion video

Lecture 4: Back - Vertebral Column

Unit 1.3: Human Gross Anatomy I - Musculoskeletal System

Learning Objectives

By the end of this lecture, students will be able to:

1. Describe the overall organization and curvatures of the vertebral column
2. Identify the structural features common to all vertebrae
3. Distinguish regional characteristics of cervical, thoracic, lumbar, sacral, and coccygeal vertebrae
4. Describe the structure and function of intervertebral discs
5. Identify the ligaments of the vertebral column
6. Explain the clinical significance of vertebral column anatomy

Overview of the Vertebral Column

The vertebral column, commonly called the spine, is the central support structure of the axial skeleton. It provides structural support for the trunk, protects the spinal cord and spinal nerve roots, serves as an attachment point for the ribs and back muscles, and permits a remarkable range of movement while maintaining stability.

The adult vertebral column consists of 33 vertebrae, of which 24 are mobile and articulate with each other through intervertebral discs and facet joints, while 9 are fused to form the sacrum and coccyx. These vertebrae are organized into five regions. The cervical region contains seven vertebrae designated C1 through C7. The thoracic region contains twelve vertebrae designated T1 through T12. The lumbar region contains five vertebrae designated L1 through L5. The sacral region consists of five fused vertebrae designated S1 through S5, which together form the sacrum. The coccygeal region typically contains four fused vertebrae, though this number varies, forming the coccyx or tailbone.

When viewed from the lateral aspect, the vertebral column displays four curvatures that increase its resilience and flexibility. Two primary curvatures are present at birth, reflecting the fetal position: the thoracic kyphosis (concave anteriorly) and the sacral kyphosis. Two secondary curvatures develop after birth in response to postural demands: the cervical lordosis (concave posteriorly) develops when an infant begins to hold the head up, and the lumbar lordosis develops when the child begins to walk upright. These curves function like a spring, absorbing vertical forces and distributing mechanical stress along the column rather than concentrating it at single points.

<image>Panel A: Lateral view of complete vertebral column showing cervical region (C1-C7) with cervical lordosis and thoracic region (T1-T12) with thoracic kyphosis curvature arrows. Panel B: Lumbar region (L1-L5) with lumbar lordosis, sacrum (5 fused vertebrae) with sacral kyphosis, coccyx (4 fused vertebrae) at inferior end. Panel C: Primary curvatures (thoracic, sacral) labeled present at birth in blue, secondary curvatures (cervical, lumbar) labeled develop postnatally in orange. Panel D: Adjacent anterior view showing straight alignment without lateral deviation, intervertebral discs visible between mobile vertebrae, scale bar indicating 70 cm average adult height.</image>

General Structure of a Typical Vertebra

Although vertebrae from different regions have distinctive features, all share a basic structural plan. Understanding this common architecture provides a foundation for appreciating regional variations.

The vertebral body, also called the corpus, is the anterior weight-bearing portion of the vertebra. It is roughly cylindrical in shape and increases in size from the cervical to the lumbar region, reflecting the progressively greater loads borne by lower vertebrae. The superior and inferior surfaces of the body are covered by cartilaginous end plates that interface with the intervertebral discs. The body consists of trabecular bone covered by a thin shell of compact bone.

The vertebral arch projects posteriorly from the body and, together with the posterior surface of the body, encloses the vertebral foramen. The vertebral foramina of all vertebrae align to form the vertebral canal, which contains and protects the spinal cord, the meninges, cerebrospinal fluid, epidural fat, and blood vessels. The arch is composed of paired pedicles and paired laminae. The pedicles are short, thick processes that project posteriorly from the posterolateral aspects of the body. The laminae are flat plates of bone that extend from the pedicles and meet in the midline posteriorly. The superior and inferior surfaces of each pedicle are notched; when adjacent vertebrae articulate, these notches align to form the intervertebral foramina, openings through which spinal nerves and vessels exit the vertebral canal.

Several processes project from the vertebral arch. The spinous process extends posteriorly from the junction of the two laminae. It serves as a lever for muscles and as an attachment point for ligaments. The transverse processes project laterally from the junction of each pedicle and lamina. They provide attachment points for muscles and, in the thoracic region, articulate with the ribs. The articular processes project superiorly and inferiorly from the junction of the pedicles and laminae. Each vertebra has two superior articular processes and two inferior articular processes. The articular surfaces on these processes, called facets or zygapophyses, form synovial joints with the articular processes of adjacent vertebrae. The orientation of these facets varies by region and determines the types and ranges of movement permitted.

<image>Panel A: Superior view of L3 vertebra showing kidney-shaped body, paired pedicles extending posterolaterally, paired laminae meeting posteriorly, central vertebral foramen. Panel B: Superior view continued showing spinous process projecting posteriorly, paired transverse processes projecting laterally, paired superior articular processes with facets visible. Panel C: Lateral view showing body, pedicle with superior and inferior vertebral notches, lamina, spinous process, transverse process, articular processes, intervertebral foramen indicated. Panel D: Posterior view showing spinous process, transverse processes, laminae, inferior articular processes, inset with two vertebrae articulating and spinal nerve exiting intervertebral foramen.</image>

Cervical Vertebrae

The cervical vertebrae (C1-C7) form the skeletal support of the neck. They are the smallest and most mobile vertebrae, adapted for the extensive range of head movements required for vision, hearing, and feeding.

All typical cervical vertebrae share distinctive features. Their bodies are small and roughly rectangular when viewed from above, wider from side to side than front to back. The vertebral foramen is large and triangular, accommodating the cervical enlargement of the spinal cord. A unique cervical feature is the transverse foramen, a canal through each transverse process that transmits the vertebral artery, vertebral veins, and sympathetic nerves. The vertebral artery passes through the transverse foramina of C6 through C1 before entering the skull. The spinous processes of C2 through C6 are characteristically bifid, meaning they split into two tubercles at their tips. The articular facets are oriented at approximately 45 degrees to the horizontal plane, allowing a combination of flexion, extension, lateral bending, and rotation.

The atlas (C1) is highly atypical. It lacks a body and a spinous process, instead consisting of an anterior arch and a posterior arch connected by two lateral masses. The anterior arch bears a facet on its posterior surface for articulation with the dens of C2. The lateral masses bear kidney-shaped superior articular facets that articulate with the occipital condyles of the skull, forming the atlanto-occipital joints. These joints are condylar joints that permit nodding movements of the head (flexion and extension), as in signaling "yes." The inferior articular facets are flatter and articulate with C2.

The axis (C2) is distinguished by the dens, also called the odontoid process, which projects superiorly from the body. The dens represents the body of the atlas, which fuses with C2 during development. It articulates with the anterior arch of the atlas and is held in place by the transverse ligament of the atlas. The median atlantoaxial joint between the dens and the anterior arch is a pivot joint that permits rotation of the head, as in signaling "no." The axis has a large, strong spinous process that may be bifid.

C3 through C6 are typical cervical vertebrae with the characteristic features described above. C7, called the vertebra prominens, has a long, non-bifid spinous process that is easily palpable at the base of the neck and serves as a clinical landmark. Its transverse foramen is small or absent, as the vertebral artery typically enters the column at C6.

<image>Panel A: Atlas (C1) superior view showing ring structure with anterior arch, posterior arch with tubercle, no body or spinous process, paired lateral masses with kidney-shaped superior articular facets. Panel B: Axis (C2) superior and lateral views showing dens (odontoid process) projecting upward from body, strong spinous process, transverse foramina, dens height relationship to body. Panel C: Typical cervical vertebra (C4) superior view showing small rectangular body, large triangular vertebral foramen, bifid spinous process, transverse foramina with vertebral artery path. Panel D: C7 (vertebra prominens) lateral view showing long non-bifid spinous process, small transverse foramen, transition features toward thoracic morphology with 1 cm scale bar.</image>

Thoracic Vertebrae

The thoracic vertebrae (T1-T12) articulate with the ribs and form the posterior wall of the thoracic cage. Their structure reflects their role in supporting the ribcage while permitting the respiratory movements of the chest wall.

The bodies of thoracic vertebrae are heart-shaped when viewed from above and are intermediate in size between cervical and lumbar vertebrae. They increase in size progressively from T1 to T12. The vertebral foramen is circular and smaller than in the cervical region. The spinous processes are long and slender, angling sharply inferiorly so that each spinous process overlaps the vertebra below. This overlapping arrangement limits hyperextension of the thoracic spine.

The defining characteristic of thoracic vertebrae is their articulation with the ribs. Each typical thoracic vertebra bears articular facets for rib attachment at two locations. On the body, costal facets called demifacets appear at the superolateral and inferolateral corners. The head of each rib typically articulates with two vertebrae: the inferior demifacet of the vertebra above and the superior demifacet of its own numbered vertebra. On the transverse process, a transverse costal facet articulates with the tubercle of the corresponding rib. Thus, the head of rib 5, for example, articulates with the inferior demifacet of T4 and the superior demifacet of T5, while its tubercle articulates with the transverse costal facet of T5.

Several thoracic vertebrae deviate from this typical pattern. T1 has a complete superior costal facet for the first rib (which articulates only with T1) and an inferior demifacet for the second rib. T10 has only a single costal facet and may lack a transverse costal facet. T11 and T12 each have a single complete costal facet with no transverse costal facet, as the floating ribs (11 and 12) do not articulate with the transverse processes.

The articular facets of thoracic vertebrae are oriented in the coronal plane at approximately 60 degrees to the horizontal, allowing rotation but limiting flexion and extension. Combined with the stabilizing influence of the rib attachments, this orientation makes the thoracic spine the least mobile region of the column.

<image>Panel A: T6 superior view showing heart-shaped body, circular vertebral foramen smaller than cervical, long inferiorly-angled spinous process, transverse processes with transverse costal facets. Panel B: Lateral view showing body with superior and inferior costal demifacets at posterolateral corners, pedicle, transverse process with transverse costal facet, spinous process angling downward. Panel C: Rib articulation diagram showing rib head contacting demifacets of adjacent vertebrae, rib tubercle contacting transverse costal facet. Panel D: Atypical vertebrae inset showing T1 with full superior facet, T11-T12 with single complete facets, facet orientation diagram showing 60 degree coronal plane with rotation permitted.</image>

Lumbar Vertebrae

The lumbar vertebrae (L1-L5) are the largest and strongest vertebrae, adapted for bearing the weight of the upper body. The lumbar region provides both stability and mobility, permitting flexion, extension, and lateral bending while limiting rotation.

The bodies of lumbar vertebrae are massive, kidney-shaped when viewed from above, and wider from side to side than from front to back. The large cross-sectional area distributes the considerable forces transmitted through this region. The vertebral foramen is triangular and larger than in the thoracic region to accommodate the lumbar enlargement of the spinal cord and the cauda equina.

The spinous processes are short, thick, and roughly quadrilateral, projecting nearly horizontally posteriorly rather than angling inferiorly as in the thoracic region. This horizontal orientation leaves gaps between adjacent spinous processes through which lumbar puncture can be performed. The transverse processes, sometimes called costiform processes because they represent rudimentary ribs, are relatively thin and project laterally. Lumbar vertebrae lack the transverse foramina of cervical vertebrae and the costal facets of thoracic vertebrae.

Additional processes distinguish lumbar vertebrae. Mammillary processes are small rounded projections on the posterior surface of the superior articular processes, providing attachment for multifidus muscles. Accessory processes are small projections at the base of each transverse process, providing additional muscle attachment.

The articular facets of lumbar vertebrae are oriented in the sagittal plane at approximately 90 degrees to the horizontal. The superior articular facets face medially, and the inferior articular facets face laterally. This orientation allows flexion and extension but severely limits rotation. The sagittal orientation also allows the inferior articular processes to grasp the superior articular processes of the vertebra below, providing stability against forward displacement.

L5 has the largest body of any vertebra. Its body is wedge-shaped, being taller anteriorly than posteriorly, which contributes to the lumbosacral angle where the lumbar spine meets the sacrum.

<image>Panel A: L3 superior view showing large kidney-shaped body, triangular vertebral foramen larger than thoracic, short thick spinous process, transverse processes projecting laterally. Panel B: Superior articular processes with mammillary processes on posterior surface, lateral view showing massive body, pedicle, accessory process at base of transverse process. Panel C: Horizontal spinous process with gap between adjacent processes indicated as lumbar puncture site, posterior view showing mammillary and accessory processes. Panel D: L5 demonstrating wedge-shaped body taller anteriorly contributing to lumbosacral angle, facet orientation diagram showing 90 degree sagittal plane with flexion/extension permitted but rotation limited.</image>

Sacrum and Coccyx

The sacrum is a large, triangular bone formed by the fusion of five sacral vertebrae (S1-S5). It forms the posterior wall of the pelvis and transmits the weight of the upper body to the pelvic bones through the sacroiliac joints. The sacrum is oriented with its base (wider end) superior and its apex (pointed end) inferior.

The anterior surface of the sacrum is concave and smooth. The pelvic sacral foramina, four pairs of openings, transmit the anterior rami of the sacral spinal nerves. The transverse ridges visible between the foramina mark the lines of fusion between the original vertebral bodies. The sacral promontory is a prominent anterior projection of the S1 body that marks the posterior boundary of the pelvic inlet; it is an important obstetric landmark.

The posterior surface is convex and rough. The median sacral crest is a ridge in the midline formed by the fused spinous processes. The intermediate sacral crests, lateral to the median crest, represent the fused articular processes. The lateral sacral crests are the fused transverse processes. The posterior sacral foramina transmit the posterior rami of the sacral nerves.

The sacral canal is the continuation of the vertebral canal through the sacrum, containing the cauda equina and the filum terminale. The canal terminates at the sacral hiatus, an opening at the lower end of the sacrum where the laminae of S5 (and sometimes S4) fail to fuse in the midline. The sacral hiatus is flanked by the sacral cornua, which represent the inferior articular processes of S5. The sacral hiatus is used for caudal epidural anesthesia.

The lateral surfaces of the sacrum bear the auricular surfaces, ear-shaped areas that articulate with the iliac bones at the sacroiliac joints.

The coccyx is a small triangular bone formed by the fusion of typically four (range of three to five) rudimentary vertebrae. It articulates with the apex of the sacrum at the sacrococcygeal joint. The coccyx provides attachment for the gluteus maximus muscle and the coccygeal ligament. Injury to the coccyx can result in coccydynia, persistent pain in the tailbone region.

<image>Panel A: Anterior view of triangular sacrum with sacral promontory at S1, four pairs of pelvic sacral foramina with transverse ridges between, auricular surface on lateral aspect, coccyx at apex. Panel B: Posterior view showing median sacral crest (fused spinous processes), intermediate and lateral sacral crests, four pairs of posterior sacral foramina. Panel C: Sacral hiatus at inferior end where laminae fail to fuse, flanked by sacral cornua, coccyx articulating below. Panel D: Lateral view showing curved shape with concave anterior and convex posterior surfaces, auricular surface for sacroiliac joint, sacral canal cross-section, inset of sacral hiatus for caudal epidural approach.</image>

Intervertebral Discs

Intervertebral discs are fibrocartilaginous joints that connect adjacent vertebral bodies from C2 to S1. There are 23 discs in total, with no disc between the skull and C1 or between C1 and C2. The discs contribute approximately 25% of the total height of the vertebral column, although this proportion decreases with aging and throughout the day as the discs are compressed.

Each intervertebral disc consists of two components. The nucleus pulposus is the central gelatinous core, composed of a highly hydrated gel containing proteoglycans, type II collagen, and water (70-90% water content in young individuals). The nucleus is a remnant of the embryonic notochord. It functions as a hydraulic shock absorber, distributing compressive forces across the disc and allowing the disc to change shape during movement. When the spine flexes, the nucleus shifts posteriorly; during extension, it shifts anteriorly.

The anulus fibrosus is the outer fibrous ring that surrounds and contains the nucleus pulposus. It consists of 15-25 concentric layers called lamellae. Each lamella is composed of type I collagen fibers arranged in parallel, but the orientation of fibers alternates between adjacent lamellae at approximately 30 degrees to the horizontal. This arrangement provides exceptional resistance to rotational forces. The outermost layers of the anulus fibrosus are firmly attached to the vertebral bodies and contain sensory nerve endings, making tears of the outer anulus painful.

The discs are avascular in adults, receiving their nutrition through diffusion from blood vessels in the vertebral end plates. This limited blood supply contributes to the poor healing capacity of damaged discs. With aging, the nucleus pulposus loses water content and becomes more fibrous, reducing its shock-absorbing capacity and making the disc more susceptible to degeneration and herniation.

The functions of the intervertebral discs include shock absorption (cushioning the vertebral column against vertical forces), load transmission (distributing weight across the vertebral bodies), and movement facilitation (allowing flexion, extension, lateral bending, and limited rotation between adjacent vertebrae).

<image>Panel A: Sagittal section through two vertebrae showing nucleus pulposus as blue-white gelatinous core surrounded by anulus fibrosus concentric rings, vertebral end plates between disc and bone. Panel B: Superior view of disc showing central nucleus pulposus surrounded by lamellae with alternating fiber direction, magnified view of collagen fibers at alternating 30 degree angles. Panel C: Disc behavior during movement with flexion shifting nucleus posteriorly and extension shifting nucleus anteriorly. Panel D: Comparison of young healthy disc with well-hydrated nucleus versus aged degenerated disc with dessicated nucleus and reduced height, nutrition pathway showing diffusion from end plate blood vessels.</image>

Ligaments of the Vertebral Column

Multiple ligaments reinforce the vertebral column, limiting excessive movement and providing stability while still allowing the flexibility necessary for normal function.

The anterior longitudinal ligament is a strong, broad band running along the anterior surface of the vertebral bodies and intervertebral discs from the skull to the sacrum. It is firmly attached to the vertebral bodies and more loosely attached to the discs. This is the strongest ligament of the spine. It limits hyperextension and prevents anterior displacement of vertebrae.

The posterior longitudinal ligament runs along the posterior surface of the vertebral bodies within the vertebral canal, from C2 to the sacrum. It is narrower than the anterior longitudinal ligament and is attached to the intervertebral discs rather than to the bodies themselves. It limits hyperflexion. Because the posterior longitudinal ligament is narrower over the bodies and wider over the discs, it provides less support posterolaterally, which is why disc herniations most commonly occur in a posterolateral direction.

The ligamentum flavum connects the laminae of adjacent vertebrae, forming part of the posterior wall of the vertebral canal. Its high elastin content gives it a distinctive yellow color (flavum means yellow in Latin) and allows it to stretch during flexion and recoil during extension without buckling into the canal. It helps maintain the upright posture and limits flexion.

The interspinous ligaments connect adjacent spinous processes, running between the root and apex of each process. They limit flexion. The supraspinous ligament runs along the tips of the spinous processes from C7 to the sacrum. In the cervical region, it is continuous with the nuchal ligament, a strong, elastic midline septum extending from C7 to the external occipital protuberance. The nuchal ligament supports the weight of the head and provides attachment for muscles.

The intertransverse ligaments connect adjacent transverse processes. They are relatively weak and limit lateral flexion.

<image>Panel A: Sagittal section showing anterior longitudinal ligament as thick band running along anterior surface of bodies and discs firmly attached to bone. Panel B: Posterior longitudinal ligament as thinner band on posterior surface of bodies, narrower over bodies and wider over discs, posterolateral disc herniation pathway indicated. Panel C: Ligamentum flavum (yellow indicating elastin) connecting adjacent laminae, interspinous ligament between processes, supraspinous ligament along tips. Panel D: Inset showing nuchal ligament from C7 to external occipital protuberance, transverse section with intertransverse ligament, arrows indicating movements limited by each ligament.</image>

Joints of the Vertebral Column

The vertebral column contains several types of joints that work together to provide stability and mobility.

The joints between vertebral bodies are the intervertebral joints, which are secondary cartilaginous joints (symphyses). The vertebral bodies are connected by the intervertebral discs. Each individual joint allows only limited movement, but the cumulative effect of movement at all 23 discs provides the spine with significant overall flexibility.

The zygapophyseal joints, commonly called facet joints, are synovial plane joints formed between the articular processes of adjacent vertebrae. Each joint is surrounded by a fibrous capsule lined with synovial membrane. These joints guide and limit the movements of the spine according to the orientation of their articular surfaces, which varies by region. In the cervical region, the facets are oriented at approximately 45 degrees, allowing flexion, extension, lateral bending, and rotation. In the thoracic region, the facets are oriented at approximately 60 degrees in the coronal plane, favoring rotation while limiting flexion. In the lumbar region, the facets are oriented at approximately 90 degrees in the sagittal plane, allowing flexion and extension while limiting rotation.

The atlanto-occipital joints are formed between the occipital condyles of the skull and the superior articular facets of the atlas. These are condylar synovial joints that allow flexion and extension of the head (nodding "yes"), with some lateral bending.

The atlantoaxial joints include three articulations between C1 and C2. The median atlantoaxial joint is a pivot joint between the dens of the axis and the anterior arch of the atlas. It allows rotation of the head (shaking "no"). The paired lateral atlantoaxial joints are plane joints between the articular facets of the atlas and axis. The transverse ligament of the atlas holds the dens against the anterior arch, preventing posterior displacement that could damage the spinal cord.

The lumbosacral joint (L5-S1) bears considerable load and is reinforced by strong iliolumbar ligaments connecting L5 to the ilium.

The sacroiliac joints are the articulations between the auricular surfaces of the sacrum and the iliac bones. Each joint has both synovial and syndesmotic components and is reinforced by exceptionally strong ligaments. These joints transmit the weight of the trunk to the pelvis and lower limbs.

<image>Panel A: Lateral view of three vertebrae showing intervertebral joints (symphyses between bodies via discs) and zygapophyseal joints (synovial joints between articular processes). Panel B: Three panels showing facet orientation by region with cervical 45 degrees allowing multiple movements, thoracic 60 degrees favoring rotation, lumbar 90 degrees favoring flexion/extension. Panel C: Atlanto-occipital joint with occipital condyles on atlas facets showing flexion/extension, atlantoaxial joints showing median dens pivot and lateral plane joints with rotation. Panel D: Lumbosacral joint with iliolumbar ligaments, sacroiliac joint showing synovial and syndesmotic components with strong posterior ligaments.</image>

Movements of the Vertebral Column

The vertebral column permits four basic movements, with the range of motion varying by region depending on disc thickness, facet orientation, and the presence of stabilizing structures.

Flexion is forward bending, most extensive in the cervical and lumbar regions. It is limited by the posterior longitudinal ligament, ligamentum flavum, interspinous ligaments, and tension in the back muscles. Extension is backward bending, also greatest in the cervical and lumbar regions. It is limited by the anterior longitudinal ligament and contact between the spinous processes. Lateral flexion is side bending, occurring throughout the column but greatest in the cervical and lumbar regions. It is limited by the intertransverse ligaments. Rotation is turning around the vertical axis, greatest in the cervical region (especially at the atlantoaxial joint) and in the thoracic region. Rotation is severely limited in the lumbar region by the sagittal orientation of the facet joints.

The thoracic region is the least mobile portion of the vertebral column due to the attachment of the ribs and the coronal orientation of the facet joints. The cervical region is the most mobile, with significant range in all movements.

Clinical Correlations

Disc herniation occurs when the nucleus pulposus protrudes through a tear in the anulus fibrosus. Because the posterior longitudinal ligament is narrower posterolaterally, herniation typically occurs in a posterolateral direction, where the nucleus can compress the spinal nerve root as it exits through the intervertebral foramen. The most common sites are L4-L5 and L5-S1, where herniation can cause sciatica, pain radiating down the leg in the distribution of the affected nerve root. Cervical disc herniations can cause radicular symptoms in the upper limb.

Spondylolisthesis is the forward displacement of one vertebra on the one below, most commonly occurring at L5-S1. It may result from a defect in the pars interarticularis (the portion of lamina between the superior and inferior articular processes), from degenerative changes in the facet joints, or from congenital abnormalities. Symptoms include low back pain and, if the displacement is significant, compression of nerve roots.

Spinal stenosis is narrowing of the vertebral canal that compresses the neural structures within. It may result from degenerative changes including disc bulging, osteophyte formation, and thickening of the ligamentum flavum. Symptoms include neurogenic claudication, pain and weakness in the legs that is worsened by walking and relieved by sitting or bending forward.

Abnormal curvatures include scoliosis (lateral deviation of the spine), excessive kyphosis ("hunchback," often from vertebral compression fractures in osteoporosis), and excessive lordosis ("swayback"). These conditions may be structural or postural and can cause pain and functional limitation.

Cervical spine injuries require special attention due to the vulnerability of the spinal cord at this level. Jefferson fracture is a burst fracture of the atlas ring caused by axial loading, as when diving into shallow water. Hangman's fracture is a bilateral fracture of the pars interarticularis of C2 caused by hyperextension, classically from hanging. Odontoid fractures involve the dens of C2 and are particularly dangerous because instability at this level threatens the adjacent spinal cord.

<image>Panel A: Disc herniation sagittal and axial views showing nucleus pulposus protruding posterolaterally through torn anulus fibrosus, compressing nerve root, common levels L4-L5 and L5-S1 marked. Panel B: Spondylolisthesis lateral view showing L5 displaced anteriorly on S1 with pars interarticularis defect and nerve root compression at narrowed foramen. Panel C: Spinal stenosis axial view showing narrowed vertebral canal from disc bulging, osteophytes, and thickened ligamentum flavum compressing cauda equina. Panel D: Abnormal curvatures showing scoliosis with lateral deviation and rotation, excessive kyphosis (hunchback), excessive lordosis (swayback) with normal spine comparison.</image>

Summary

The vertebral column consists of 33 vertebrae organized into five regions: seven cervical, twelve thoracic, five lumbar, five sacral (fused), and four coccygeal (fused). Four curvatures provide resilience: primary curvatures (thoracic and sacral kyphosis) present at birth, and secondary curvatures (cervical and lumbar lordosis) developing postnatally.

Typical vertebrae have a body for weight-bearing, a vertebral arch (pedicles and laminae) enclosing the vertebral foramen, and processes for muscle and ligament attachment. Cervical vertebrae are characterized by transverse foramina and bifid spinous processes; the atlas (C1) lacks a body, and the axis (C2) has the dens. Thoracic vertebrae have costal facets for rib articulation. Lumbar vertebrae are the largest, with sagittal-plane facets limiting rotation.

Intervertebral discs consist of a nucleus pulposus (shock absorption) surrounded by an anulus fibrosus (containment). Major ligaments include the anterior and posterior longitudinal ligaments, ligamentum flavum, and interspinous ligaments. Facet joints are synovial joints whose orientation determines regional mobility. Clinical conditions include disc herniation, spondylolisthesis, spinal stenosis, and abnormal curvatures.

Key Terms

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