HISTOLOGIC-CHANGES IN THE INTERVERTEBRAL DISC AFTER INTRADISCAL INJECTIONS OF METHYLPREDNISOLONE ACETATE IN RABBITS

Study Design. Histologic changes in the intervertebral disc were evalu ated by light and electron microscopy after an intradiscal injection o f methylprednisolone acetate. Objective. To evaluate the histologic ch anges that occur in the disc after an intradiscal injection of cortico steroids. Summary of Background Data. Several orthopedic surgeons have managed lumbar disc herniation with intradiscal steroid injection. Fe w studies have addressed the histologic changes after this treatment. Methods. Thirty rabbits were surgically treated. Rabbits were divided into two groups. Group A: 25 rabbits underwent intradiscal steroid inj ections. Methylprednisolone acetate wits injected into the L3-L4 disc, whereas methylprednisolone sodium succinate was injected into the L4- L5 disc. Physiologic saline was injected into the L5-L6 disc as a cont rol. Groups of five rabbits were killed 1 day, 1, 4, 12, and 24 weeks after the injection and subjected to microscopic evaluation. Group B: Another five rabbits underwent-an injection of polyethylene glycol 400 0, a vehicle for methylprednisolone acetate, into the L3-L4 and L4-L5 discs. All five rabbits were killed 24 weeks after the injection and s ubjected to microscopic evaluation. Results. Group A: Light microscopi c evaluation showed tissue in the nucleus pulposus, and the inner laye r of the anulus fibrosus had degenerated in the methylprednisolone ace tate group killed 24 weeks after the injection. Matrix vesicles, an in dication of primary tissue calcification, were observed by electron mi croscopy. in the methylprednisolone sodium succinate group and saline group, however, no histologic changes were observed. Group B: Degenera tion of the nucleus pulposus and primary tissue calcification were obs erved in the discs of atl rabbits. Conclusions. Methylprednisolone ace tate and its vehicle polyethylene glycol cause degeneration and primar y calcification in discs.