Variations in size of the bony lumbar canal in patients with prolapse of lumbar intervertebral discs.

Prolapse of the lumbar intervertebral disc is one of the commonly accepted causes of low back pain. Most patients respond well to conservative treatment, but some may not respond at all. Though the reason for this variation is not clearly understood, it is felt that a developmentally narrow spinal canal might have some relation to the persistence of backache and sciatica. The canal was therefore measured at each of the lumbar vertebral level by a method described by Jones and Thomson (1969) in 100 consecutive patients operated upon for prolapsed lumbar intervertebral discs, in 100 normal patients for comparison. This method does not give direct measurements of the bony spinal canal but provides a ratio of the size of the canal to the adjacent vertebral body. We found a trend towards the presence of a narrower than normal lumbar canal in patients with prolapsed lumbar intervertebral discs. It is concluded that in patients with prolapsed lumbar intervertebral discs necessitating operation, the canal tends to be narrower than normal, and such narrowing enhances the effect of any disc protrusion leading to severe symptoms of backache and sciatica.