Introduction and relevant anatomy
L4–L5 intervertebral disc prolapse is displacement of disc material beyond the normal margins of the L4–L5 disc, with potential compression or irritation of adjacent neural structures. It is a common cause of low-back pain and lumbar radiculopathy. The usual posterolateral lesion compresses the traversing L5 nerve root in the lateral recess or at the level of the L5 pedicle. In contrast, a foraminal or far-lateral L4–L5 prolapse may compress the exiting L4 nerve root.
The L4–L5 motion segment consists of the L4 and L5 vertebral bodies, the intervertebral disc, paired facet joints, ligamentum flavum, posterior longitudinal ligament and the neural canal. The disc contains a gelatinous nucleus pulposus surrounded by concentric fibrocartilaginous lamellae of the annulus fibrosus. With age and mechanical stress, disc hydration and proteoglycan content decline, fissures develop in the annulus, and the nucleus may migrate posteriorly. Posterolateral displacement is favoured because the posterior annulus is relatively weaker and the posterior longitudinal ligament is narrower laterally.
Pathology and pathophysiology
Disc prolapse produces symptoms through two interacting mechanisms:
- Mechanical compression: the displaced fragment narrows the lateral recess, intervertebral foramen or central canal and compromises the nerve root.
- Chemical radiculitis: exposed nucleus pulposus induces an…