RESUMO
PURPOSE: To determine the upper limit of peripheral nerve lengthening without loss of function, the recovery time of peripheral nerve palsy due to nerve lengthening and their histological changes. MATERIALS AND METHODS: Twelve adult New Zealand rabbits weighing about 2.5 kg were assigned to the following groups. Group 1 (n=6) was subjected to slow tissue expansion with 30% of nerve lengthening while group 2 (n=6) was rapid expansion with 40% lengthening of nerve. The expanders were refilled every 2 times during the 2nd and 4th weeks making a total four times of expansion. The rabbits were assessed in terms of affected leg paralysis, neural length gain, EMG with nerve conduction velocity and histological changes. RESULTS: In group 1 (n=6), paralysis on affected leg was found in one rabbit and was recovered spontaneously on the 4th weeks after expander removal. In Group 2 (n=6), paralysis was found in four rabbits, and three of them were recovered on 4, 5 and 9 weeks after removal of the expander. EMG study showed increase in distal latency of 2.50+/- 0.20 m/sec, and decrease in nerve conduction velocity of 62.49+/- 5.30 m/sec compared to normal side with 1.89+/- 0.14 m/sec and 75.39+/- 7.82 m/sec. The mean neural length gain was 6 mm (30% of 20 mm of initial pre-experimental nerve length) in group 1 and 8 mm (40% of 20 mm) in group 2. Light microscopic examination revealed the loss of segmental myelination, decrease of myelination, and vacuolation. Electron microscopic examination showed that the normal ring shaped contour of axon was changed to convoluted shape.