Protrusion of the posterior longitudinal ligament simulating herniated lumbar intervertebral disc.

The most common cause of lumbar or sacral nerve-root compression probably is herniation of the nucleus pulposus. There are some patients with typical clinical-and even radiological-evidence of ne'rVe root compression, however, in whom no herniation is found at operation; instead the nerve root is compressed by a fold in the posterior longitudinal ligament, and, when this is excised, there is