The relationship of structural pathology to the nerve root.

Lumbar spinal nerves may be entrapped (a) at the back of the disc (b) laterally in the central canal, (c) in the cauda equina, (d) more laterally in the nerve canal, and (e) posteriorly in the zygapophyseal joints. There is a spectrum of degenerative change in both joints and disc. Changes at these three sites can produce (a) dysfunction, (b) disc herniation, (c) instability, (d) lateral entrapment, and (e) central stenosis. The clinical significance is that many patients become symptom free on nonoperative treatment. Some with nerve entrapment require decompression. Those with instability may need a fusion. The pain from a disc lesion or from stenosis may come from irritation and inflammation of the dura. The motor loss in these lesions may be due to reflex inhibition and vascular insufficiency rather than from nerve compression. It is vitally important to identify accurately the nerve that is entrapped.