ANALYSIS OF PERIDURAL SCAR FORMATION AND ITS PREVENTION AFTER LUMBAR LAMINOTOMY AND DISKECTOMY IN DOGS

Study Design. Peridural fibrosis after lumbar laminectomy and discecto my has been implicated (not proven) as one of the factors that contrib ute to continuing or recurrent radicular and/or low back pain, This an imal experimental study was designed to unequivocally show the stages in the development of scar tissue and to what extent, if any, scar tis sue development is influenced by interposing fat grafts and Na hyaluro nate of different molecular weights. Methods. A four-level unilateral lumbar laminotomy, anular fenestration, and nucleotomy was performed i n 11 dogs, In each dog, levels were selected at random: one to serve a s an empty control and three to insert the following: a fat graft, a v iscous (1.9%) solution of Na hyaluronate, and a 1% high molecular weig ht solution of Na hyaluronate solution. The animals were killed at 1 d ay, 2 days, and 1, 2, 4, and 12 weeks postoperatively. immediately aft er the dogs were killed, the lumbar spines were frozen in situ with dr y ice, the lumbar spines were harvested and sectioned with a cryomicro tome. Close-up photographs taken at submillimeter intervals at each le vel were digitized and postprocessed with a computer. Results. In the early postoperative period a hematoma was found in the pathway of the surgical dissection. During a 2-4-week period, this hematoma was repla ced by a thick, white fibrotic tissue mass. Fibrosis was markedly less pronounced at the hyaluronate levels, especially the high molecular w eight subset, Two-way statistical analysis of variance without replica tions revealed significantly less scar formation at the 0.05 level in the hyaluronate vs. the control segments. Dunnett's test, comparing ea ch group individually with the control, revealed no difference between the fat groups and the control subjects, There was a significant diff erence between 1.9% Na hyaluronate and control. Conclusions, Viscous h yaluronate solution with its semifluid properties coats the nerve root s and dura anteriorly and posteriorly and reduces peridural fibrosis i n the critical anterior region where adhesions form between the nerve root and anulus fibrosus.