disc prolapse (intervertebral)
Prolapsed intervertebral disc is a condition where the gelatinous nucleus pulposus squeezes through the annulus fibrosus and bulges in a posterior or posterolateral direction, beneath the posterior longitudinal ligament. This causes pressure symptoms on the root below the level of herniation - most commonly S1, then L5, then L4. Other defects are rarer, and higher defects ought to be investigated for other causes.
Last reviewed 01/2018