Trunk (thorax, abdomen, back)

Anulus fibrosus of lumbar intervertebral discs (L1–S1)

Anulus fibrosus disci intervertebralis (pars lumbalis)

Origin

15–25 concentric fibrocartilage lamellae with alternating 30° fiber orientation anchored to superior lumbar vertebral rim

Insertion

Attached via Sharpey fibers to the inferior lumbar vertebral body or sacrum (L5-S1)

Function

Bears high axial loads, retains hydrostatic pressure of nucleus pulposus, and limits excessive lumbar rotation

Innervation

Sinuvertebral nerves and gray rami communicantes (outer third)

Movement & chain

Deforms under axial compression, bending, and lifting loads

Palpation

Not palpated directly

Clinical

Annular fissures (discogenic back pain); lumbar disc herniation (most common at L4-L5 and L5-S1) causing sciatica / radiculopathy; cauda equina syndrome (red flag surgical emergency).

Segmental innervation

L1–S1

In clinical practice

McKenzie therapy, core stability training, ergonomics, and post-discectomy rehabilitation

Region in the model

Trunk (thorax, abdomen, back)