Home › Body Atlas › Joints › Posterior Annular Fibres (Lumbar Disc)

Posterior Annular Fibres (Lumbar Disc)

fibrae anuli fibrosi posteriores (discus intervertebralis lumbalis)

The posterior annulus is the critical zone for disc herniation, posterolateral fibres lack PLL reinforcement and experience the highest tensile forces during lumbar flexion with rotation. Sequential fibre failure produces the radial fissure through which the nucleus pulposus herniates to compress adjacent nerve roots. The posterolateral herniation at L4-L5 and L5-S1 compresses the L5 and S1 roots respectively.

Anatomical Data

Structure

Bones	Ring apophyses and endplates of adjacent lumbar vertebral bodies
Ligaments	Posterior longitudinal ligament (reinforces it centrally, leaving the posterolateral corners less supported)

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

L4-L5 posterolateral disc herniation compresses the traversing L5 root (not the exiting L4) producing foot dorsiflexion weakness, first toe weakness, and lateral leg numbness. L5-S1 herniation compresses S1 producing ankle plantarflexion weakness, reduced Achilles reflex, and lateral foot numbness. Discectomy removes the herniated fragment, the remaining annulus heals over 6-8 weeks.

Pathology

Common Injuries & Conditions

Posterolateral Disc Herniation

Posterior annulus radial tear allowing nucleus herniation to compress traversing nerve root managed with conservative physiotherapy or microdiscectomy for refractory radiculopathy.

Explore

More in Lower Back

Browse all of Lower Back →