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.
| Origin | Anterior vertebral body endplate (inferior) |
|---|---|
| Insertion | Anterior vertebral body endplate (superior of adjacent vertebra) |
| Actions | Resists anterior disc bulge; reinforces the anterior disc against extension loading; the 15-20 concentric lamellae resist multidirectional forces through alternating collagen fibre orientations |
|---|
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.
Full-thickness posterior annulus tear (high-intensity zone on MRI) producing discogenic pain managed with intradiscal procedures or functional restoration.
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