Repair of peripheral nerve defect with direct gradual lengthening of the proximal nerve stump in rats.

We investigated the effect of direct gradual lengthening on the proximal nerve stump and subsequent nerve regeneration in rats. A 10-mm-long nerve segment was resected from the sciatic nerve of each rat. The proximal nerve stump was directly lengthened at a rate of 1 mm/day using an original external nerve distraction device. Experiment I: After distraction periods of 10, 15, and 20 days, the length of each nerve was evaluated, and the lengthened nerve stump was also examined by immunohistochemical analysis. Experiment II: After a distraction period of 20 days, both nerve stumps were refreshed and direct end-to-end neurorrhaphy was performed. For control, 10-mm nerve grafting was immediately performed after nerve resection. Nerve regeneration was evaluated electrophysiologically and histologically 7, 9, and 15 weeks after nerve resection in both groups. The whole proximal nerve stump, including the endoneurium and the axon, could be lengthened in proportion to the distraction period. There were no significant differences in motor nerve conduction velocity and tetanic muscle contraction force between both groups. Histologically, the total number of myelinated fibers was significantly greater in the nerve lengthening group than in the autografting group. This study demonstrated that the whole proximal nerve stump including the endoneurium and the axon could be lengthened by direct gradual distraction, and that this method might have potential application in the repair of peripheral nerve defects.