PERIPHERAL-NERVE REGENERATION - THE EFFECTS OF POSTOPERATIVE IRRADIATION

The purpose of this study was to evaluate the effects of postoperative external cobalt-60 beam irradiation on nerve regeneration. Sixty-five 250-gm male Sprague-Dawley rats were studied. Peripheral nerve regene ration was measured by walking track analysis and histomorphology of t he proximal, graft, and distal nerve segments. These 65 animals underw ent a 1.5-cm interpositional nerve graft into the right posterior tibi al nerve. The left leg served as a control. Each animal was then rando mly allocated into one of four groups. Group 1 served as control. Grou ps 2 through 4 were subjected to external cobalt-60 gamma-ray irradiat ion through a 2.5-cm circular portal for a total fractionated dose of 30, 50, and 70 Gy beginning on postoperative day 3. Radiation was admi nistered in 2-Gy fractions, 5 fractions per week, with a top-up dose o f 16 Gy given at the end of the fractionated irradiation. Walking trac k analysis was performed at 30, 60, 90, and 120 days after nerve graft ing. At the conclusion of 120 days, sections of the proximal, grafted, and distal nerve were harvested, stained, and examined histomorpholog ically. Hematoxylin and eosin stains also were obtained. Evaluation of the print-length index demonstrated no statistical difference between the unirradiated controls and the irradiated groups. The total number of axons per square millimeter and nerve fiber density per square mit limeter were significantly decreased in the distal segment of all the irradiated groups when compared with controls. Despite the reduction in myelinated regenerating fibers, no reduction in function was observ ed, as measured by walking track analysis. We would therefore recommen d immediate reconstruction of peripheral nerve defects in the face of postoperative irradiation.