THE EFFECTS OF NORMAL, FROZEN, AND HYALURONIDASE-DIGESTED NUCLEUS PULPOSUS ON NERVE ROOT STRUCTURE AND FUNCTION

Study design. Autologous nucleus pulposus was modified and applied to the cauda equina in pigs, Histology and neurophysiology were assessed after 7 days. Objectives. To assess if alterations of the nucleus pulp osus would change the degree and distribution of the nerve injury indu ced by autologous nucleus pulposus. Summary of background data. It was reported recently that nucleus pulposus may induce structural and fun ctional changes in nerve roots after epidural application,The basic me chanisms causing these changes are not fully understood. Methods. Nucl eus pulposus was harvested from lumbar discs and submitted to either o f three treatments; 37 C for 24 hours (n = 5), -20 C for 24 hours (n = 5), or digestion by hyaluronidase for 24 hours (n 6), In two addition al pigs, nucleus pulposus was applied just after harvest as a control to verify previous observations. After 7 days, nerve conduction veloci ty was recorded, and specimens were processed for blinded light micros copic assessment. Results. When nucleus pulposus was applied just afte r harvest, or when it had been kept at 37 C or digested by hyaluronida se for 24 hours, there was a significant reduction in nerve conduction velocity similar to previous observations. When nucleus pulposus had been kept at -20 C for 24 hours, however, there was no reduction in co nduction velocity. There were no apparent differences between the grou ps at the histologic assessment. Staining of the nucleus pulposus show ed that the cells in the nucleus pulposus exposed to -20 C were lysed, whereas the cells in the nucleus pulposus treated by the two other me thods were mainly unaffected. Conclusions. Because freezing of the nuc leus pulposus probably kills the cells but does not affect other compo nents, one may assume that the biologic effects induced by the nucleus pulposus may be related to its cell population.