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Anterior Annular Fibres (Lumbar Disc)

fibrae anuli fibrosi anteriores (discus intervertebralis lumbalis)

The lumbar annulus fibrosus consists of 15-20 concentric lamellae of type I collagen with alternating fibre orientations (55-60 degrees to vertical in adjacent layers). The anterior annulus is reinforced by the ALL and is rarely the site of herniation, posterior and posterolateral annular fissures from flexion-rotation loading produce the disc herniations that compress nerve roots. The annular tear (high-intensity zone on T2 MRI) indicates a full-thickness posterior annular fissure.

Anatomical Data

Structure

Bones	Ring apophyses and endplates of adjacent lumbar vertebral bodies
Ligaments	Anterior longitudinal ligament (reinforces it in front)

Biomechanics

Function & Actions

Movements	Small flexion and extension Small lateral flexion Small rotation Resists these movements at the end of range

Clinical Relevance

Clinical Notes

The high-intensity zone (HIZ) on T2-weighted MRI, a focal bright signal in the posterior annulus, indicates a full-thickness posterior annular fissure with granulation tissue. It has a high positive predictive value for concordant provocation discography and is an imaging surrogate for discogenic pain. Intradiscal therapies (steroid injection, biologics, stem cells) target this annular pathology.

Pathology

Common Injuries & Conditions

Posterior Annular Fissure

Full-thickness posterior annulus tear (high-intensity zone on MRI) producing discogenic pain managed with intradiscal procedures or functional restoration.

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