THE ETIOLOGY OF FOCAL SPINAL ARACHNOIDITIS - AN EXPERIMENTAL-STUDY

Focal arachnoiditis and back pain have been attributed to potentially irritating substances leaking into the spinal canal from the lumbar in tervertebral disc or facet joints. Through experimentation this hypoth esis was tested: the nucleus pulposus (escaping from the intervertebra l disc), lactic acid (from anaerobic glycolysis in the disc), chondroi tin sulfate (a component of glycosaminoglycans in the disc), or synovi al fluid (from degenerating facet joints) causes inflammation in the m eninges if it contacts the dura mater. The test and control substances were injected into the epidural space of monkeys. Twelve weeks later the animals were killed; the dural sac was exposed by total lumbar lam inectomy, grossly inspected, and then removed, fixed, sectioned, stain ed, and examined microscopically. Nucleus pulposus produced significan t fibrosus in the arachnoid and epidural spaces; the other substances did not cause fibrosus or inflammation. The study suggests that leakag e of nucleus pulposus into the epidural space causes an inflammatory r esponse in the arachnoid and epidural spaces.