THE EFFECTS OF PREOPERATIVE IRRADIATION ON PERIPHERAL-NERVE REGENERATION

The purpose of this study was to evaluate the effects of preoperative external cobalt(60) beam irradiation on nerve regeneration. Ninety 250 -g male Sprague-Dawley rats were studied. Peripheral nerve regeneratio n was measured by walking track analysis and histomorphology of the pr oximal, grafted, and distal nerve segments. Ninety animals were random ly assigned to one of five treatment groups, receiving a total fractio nated dose of 30, 50, 70, and 90 Gy. Each animal received a 15-mm inte rposition nerve graft into the right posterior tibial nerve 6 weeks fo llowing completion of radiation therapy, The left leg served as a cont rol. The remaining 10 animals received a nerve isograft subjected to a single dose of 30 Gy prior to placement (group 5). Walking track anal ysis was performed monthly through 8 months. At the conclusion of 120 and 240 days, sections of the proximal, grafted, and distal nerve were harvested, stained, and examined histomorphologically. Evaluation of the print length index demonstrated no statistical difference between our previously established nonirradiated controls, the irradiated grou ps, and the irradiated isograft group (group 5). The total number of a xons per square millimeter was significantly decreased in the distal s egment of all irradiated groups when compared with the controls. No st atistical difference in number of axons per square millimeter was note d in the irradiated isograft group. Furthermore, no statistical differ ence was noted in the nerve fiber density between the control group, t he preoperative irradiated groups, or the irradiated isograft group (g roup 5). Despite the reduction in myelinated regenerating fibers, no r eduction in function was observed as measured by walking track analysi s. Thus, immediate reconstruction of peripheral nerve defects in the f ace of preoperative irradiation may not be contraindicated.