Chemonucleolysis--an experimental histopathological study.

To investigate the histopathological changes of the intervertebral disc after chemonucleolysis, experiments were performed on 21 monkeys. After the injection of chymopapain, animals were sacrificed at definite intervals up to 1 year. Histopathological studies on these specimens revealed disappearance of proteoglycan from the nucleus pulposus, inner annulus fibrosus and cartilaginous endplates as early as 1 day after injection. At 4 weeks, regeneration of proteoglycan was indicated by the recovery of positive Safranin-O (S-O) staining in the area of the nucleus pulposus. After 24 weeks, the entire intervertebral disc showed uniform S-O staining indicating further regeneration of proteoglycan. The matrix of the reformed nucleus pulposus contained increased amount of fibrous elements compared to the controls. These results indicate proteoglycan regeneration by chondrocytes after chemonucleolysis. The reformed nucleus was histopathologically different from the control.