Experimental study on slow-speed elongation injury of the peripheral nerve: electrophysiological and histological changes.

Slow-speed elongation of the sciatic nerves was induced in 41 rabbits by lengthening the osteotomized femur by 2.1 mm/day with an external fixator. Time courses were monitored. About 2 weeks after elongation began, the amplitude of the compound nerve action potentials decreased, and delayed latency began. Histological observations showed that the wavy structure of the nerve fibers was lost during the stage at which reduction in the amplitude of action potentials occurred. In some nerve fibers, narrowing of the axons was observed. Further elongation caused delay in the percent latency. Histologically, collagen fibers were noted in the nerve fascicles, as well as narrowing in all the nerve fibers. When elongation ceased at the stage at which a reduction in the amplitude of action potential was noted, recovery from nerve damage followed. When elongation did not cease until the stage at which latency was delayed, however, recovery was not apparent, either histologically or electrophysiologically. The critical level of percent amplitude for recovery was at 82.4% of the original level (the critical rate for bone lengthening was 20.5%).