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principle

Principle

There is no clear, single explanation as to why a disk rupture causes back pain and / or sciatica. Some disk ruptures remain asymptomatic. The patient’s major complaint is pain. But physical pressure on a peripheral nerve alone does not produce pain; it produces paresthesia. In examining this problem further, at the conclusion of routine laminectomy for herniated nucleus pulposus, Macnab instituted the placement of a Fogarty catheter underneath the emerging nerve root of a segment above the laminectomy level. When the patients had regained consciousness, and before they had been given any analgesics, the catheters were distended. It was found that although distention of the catheter underneath an involved, angry, red, inflamed nerve root reproduced the sciatic pain, distention of the catheter underneath the normal nerve root produced paresthesia only. It is likely that there are neuromechanical factors involved in explaining the mechanism of symptom production in a herniated nucleus pulposus. Periradicular injection of long-acting steroids is efficient, probably because it decreases inflammation of the epidural space.

Fig 1: Pathology of disk herniation

Fig 2: Disk herniation