EFFECTS OF STEROID AND LIPOPOLYSACCHARIDE ON SPONTANEOUS RESORPTION OF HERNIATED INTERVERTEBRAL DISCS - AN EXPERIMENTAL-STUDY IN THE RABBIT

Study Design. Histologic examination was per formed on autografted int ervertebral disc materials of rabbit models, which were partially inci sed through a retroperitoneal approach at L1-L2 and grafted within the posterior epidural space at L4. Objective. To evaluate whether the re sorption process of the herniated intervertebral disc is influenced an d controlled by treatments with medications. Summary of Background Dat a. Regarding resorption of herniated intervertebral discs, recent stud ies of magnetic resonance images and histologic investigations of surg ically resected specimens in lumber disc herniation patients have been reported. It has been shown that inflammatory factors may play an imp ortant role in the mechanism of resorption of the herniated interverte bral disc. However, little is known about the origin of newly formed v essels and inflammatory cells detected in herniated disc specimens fro m patients. In this study, The resorption process of disc material gra fted into the epidural space was observed in a rabbit model. Methods. Thirty-six adult rabbits were used. The L1-L2 intervertebral disc was partially incised through a retroperitoneal approach. The harvested di sc material, which contains the nucleus pulposus and the anulus fibros us were placed into the posterior epidural space at L4 of the same rab bit. The animals were divided into control, and steroid groups. The co ntrol group received no treatment after surgery. In the lipopolysaccha ride group, rabbits were injected 1 mg/kg into the peritoneum immediat ely and at 7 days after surgery. In the steroid group, rabbits were in jected with 1 mg/kg beta-methasone into the epidural space daily from 1 to 7 days after surgery. Rabbits of each group were killed for histo logic examination at 1, 2, 4, and 8 weeks after surgery. Results. At 1 and 2 weeks after surgery, inflammatory cells and newly formed vessel s were more frequently observed in the lipopolysaccharide group than i n the control and steroid groups. At 4 weeks after surgery, derangemen t and loosening of collagen fibers were also observed in the lipopolys accharide group. At 8 weeks after surgery, fragmentation and partial d isappearance of matrix were observed in the control and lipopolysaccha ride groups. Most of the intervertebral discs were replaced by fibrous tissues in the lipopolysaccharide group. However, the matrix of the i ntervertebral disc almost remained. Conclusions. Autologous interverte bral disc material grafted into the epidural space was penetrated by n ewly formed vessels produced from the epidural fat tissue and resolved as the result of inflammatory reaction. Lipopolysaccharide accelerate d the replacement of grafted intervertebral disc by fibrous tissue, wh ich suggests the resorption of the disc in the epidural space of the r abbit, whereas high-dose steroid suppressed the replacement.