Electrophysiological and histological investigation on the gradual elongation of rabbit sciatic nerve

A basic study using animal models was performed to investigate whether the sciatic nerve retains physiological functions and normal morphology after the gradual elongation associated with adjacent bone elongation. Electrophysiological and histological studies were performed on the elongated sciatic nerve of rabbit accompanied by the femur bone elongation. Compound action potentials evoked by electrical stimulation of the sciatic nerve were recorded and histological specimens of elongated nerve fibers were obtained immediately after final bone elongation from 4 rabbits (immediate group). Three rabbits were allowed to recover for 8 weeks after the bone elongation (maintained group). Three rabbits without bone elongation were used as controls of the immediate and maintained groups (control group). In the immediate group, the average amplitude of evoked nerve potentials were 30.38 ± 1.58 mV before elongation and diminished significantly to 18.35 ± 1.25 mV immediately after elongation (P<0.01). The amplitude of evoked potentials was not significantly different between before (30.30 ± 0.61 mV) elongation and after elongation (27.47 ± 1.63 mV) in the maintained group. The axonal area of the myelinated nerve fibers of the proximal region of the sciatic nerve in the immediate group was significantly decreased after elongation (P<0.01). The decrease in the area of the distal region was greatest in the control group and was followed by that in the maintained group and the immediate group (P<0.05, 0.01). These results suggest that the sciatic nerve shows dysfunction immediately after elongation, but can recover electrophysiologically and histologically several weeks after elongation.