EFFECTS OF METHYLPREDNISOLONE ON NUCLEUS PULPOSUS-INDUCED NERVE ROOT INJURY

Study Design. The effects of intervention by intravenous injection of methylprednisolone to reduce the nerve root injury after epidural appl ication of autologous nucleus pulposus was studied in an experimental model on the pig cauda equina in 20 animals. Methods. Nucleus pulposus was harvested from a lumbar disc. After lowering the pH of the nucleu s pulposus to 3.5 it was placed onto the sacrococcygeal cauda equina. Fifteen of the pigs received a single intravenous injection of 30 mg/k g methylprednisolone, 5 minutes, 24 hours, or 48 hours, respectively, after the application. After 7 days, the nerve conduction velocity was determined, and biopsies of the cauda equina was examined by lightmic roscopy. Results. In the five pigs that did not receive any methylpred nisolone treatment, nerve conduction velocity was reduced, whereas it was normal in the pigs treated 5 minutes and 24 hours after nucleus pu lposus application. In pigs treated after 48 hours, nerve conduction v elocity was reduced only slightly. At the light microscopic level, sig nificant changes occurred in all series. Conclusions. This study indic ates that the nucleus pulposus-induced effects on nerve function in an experimental pig model may be reduced dramatically by high-dose methy lprednisolone administration within 24-48 hours after epidural applica tion.of autologous nucleus pulposus. The light microscopic changes wer e probably not significant for the nerve function. Instead, a morpholo gic explanation on a subcellular level should probably be sought.