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Intervertebral Disc

discus intervertebralis

The intervertebral disc is a fibrocartilaginous joint between adjacent vertebral bodies consisting of a gelatinous nucleus pulposus centrally, concentric collagen lamellae of the annulus fibrosus peripherally, and cartilaginous end plates above and below. It allows limited movement between adjacent vertebrae while absorbing compressive loads on the spine. The adult disc is largely avascular and is nourished by diffusion through the end plates, which helps explain its vulnerability to degeneration. With age the nucleus dehydrates and the annulus develops fissures, predisposing to herniation and degenerative disc disease.

Anatomical Data

Structure

Bones	Adjacent vertebral bodies above and below
Ligaments	Anterior longitudinal ligament Posterior longitudinal ligament Annulus fibrosus itself serves as the primary disc ligament

Biomechanics

Function & Actions

Movements	Flexion and extension Lateral flexion Limited rotation Compression and shock absorption across the spinal column

Clinical Relevance

Clinical Notes

Intervertebral disc herniation occurs when nucleus pulposus material escapes through a defect in the annulus fibrosus and compresses adjacent nerve roots (radiculopathy) or, in the neck and thoracic spine, the cord (myelopathy). The L4 to L5 and L5 to S1 discs are most commonly herniated. The straight leg raise test stretches the L5 and S1 nerve roots and is positive when leg pain is reproduced below the knee at less than 60 degrees of hip flexion. Degenerative disc disease produces loss of disc height, end plate (Modic) changes and osteophytes. Conservative management resolves most herniations, with discectomy reserved for significant neurological deficit or failure of conservative care; disc replacement is an alternative to fusion in selected patients.

Pathology

Common Injuries & Conditions

Disc Herniation

Nucleus pulposus extrusion through an annular defect compressing nerve roots and producing radiculopathy with dermatomal leg pain, reproduced by the straight leg raise test and managed with physiotherapy and selective nerve root blocks before surgery.

Degenerative Disc Disease

Age-related disc dehydration and annular degeneration producing axial back pain, reduced spinal segment height, and predisposition to herniation, managed with exercise, manual therapy, and pain management.

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