Vertebral Column

Vertebral Column

Overview

The vertebral column comprises 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused = sacrum), and 3–4 coccygeal (fused = coccyx). Of these, 24 are mobile. Primary curvatures (thoracic kyphosis and sacral kyphosis) are present at birth. Secondary curvatures (cervical lordosis, on lifting the head; lumbar lordosis, on walking) develop postnatally. Scoliosis is an abnormal lateral curvature with vertebral rotation.

Regional Vertebral Features

Typical cervical vertebra (C3–C7): small body, bifid spinous process, triangular foramen, transverse foramina (contain vertebral arteries). Atlas (C1): no body or spinous process; anterior and posterior arches; lateral masses articulate with occipital condyles (atlantooccipital joint) and axis below. Axis (C2): has the dens (odontoid process) that projects through the atlas ring, allowing rotation.

Typical thoracic vertebra: heart-shaped body, long inferiorly directed spinous process, demifacets on body (costovertebral joints with rib heads), costal facets on transverse processes (costotransverse joints). Typical lumbar vertebra: large kidney-shaped body (bears most load), short stubby spinous process, triangular foramen, C-shaped (superior) and flat (inferior) articular processes, no transverse foramina or costal facets.

Intervertebral Discs

Each disc consists of an outer annulus fibrosus (concentric lamellae of fibrocartilage) surrounding an inner nucleus pulposus (gel-like, remnant of notochord). Discs allow compressive and bending movement and act as shock absorbers. The nucleus pulposus can herniate posterolaterally through the annulus fibrosus, compressing adjacent nerve roots. L4/L5 is the most common level, followed by L5/S1.

Ligaments and Muscles

Anterior longitudinal ligament (ALL): runs along anterior vertebral bodies, limits extension. Posterior longitudinal ligament (PLL): runs along posterior vertebral bodies inside the canal, limits flexion. Ligamentum flavum: connects adjacent laminae, limits flexion, high elastic fibre content. Supraspinous ligament: connects spinous process tips (becomes ligamentum nuchae in cervical region). Interspinous ligaments: between spinous processes.

Erector spinae (iliocostalis, longissimus, spinalis) is the primary extensor of the vertebral column.

Lumbar Puncture

Performed at L3/L4 or L4/L5 interspace (below conus medullaris at L1/L2 to avoid spinal cord injury). The needle passes through: skin → superficial fascia → supraspinous ligament → interspinous ligament → ligamentum flavum → epidural space → dura mater → arachnoid mater → subarachnoid space (CSF).