Intervertebral Disc Annulus Fibrosus

anulus fibrosus disci intervertebralis

The annulus fibrosus is the outer fibrocartilaginous ring of the intervertebral disc, consisting of concentric lamellae of collagen fibres oriented at alternating 60-degree angles to resist multidirectional loading. It contains and pressurises the nucleus pulposus.

Region: Lower Back

Biomechanics

Function & Actions

Resists tensile forces during flexion, extension, and axial rotation, contains the nucleus pulposus under axial pressure, distributes compressive loads across the endplate, and provides the primary structural integrity of the intervertebral disc.

Clinical Relevance

Clinical Notes

Annular fissures are the primary pain generators in discogenic low back pain — the outer third of the annulus is innervated by the sinuvertebral nerve and produces discogenic pain. Annular tears allow nucleus pulposus herniation producing radiculopathy. Annular repair procedures (ArthoFlex disc closure, Barricaid) aim to prevent reherniation after discectomy.

Pathology

Common Injuries & Conditions

Annular Tear and Disc Herniation

Radial or circumferential annular fissure allowing nucleus pulposus migration and eventual herniation, producing nerve root compression and radicular pain.

Discogenic Pain from Inner Annular Disruption

Annular fissure without herniation producing deep axial low back pain reproduced by discography, treated by disc replacement or intradiscal procedures in select cases.