To evaluate changes in the sciatic nerve of rabbits according to the degree of femoral lengthening.

Acute and gradual bone lengthening of the femur were performed after osteotomy, using external fixators in 36 rabbits of both sexes weighing 2, 500 gm. According to the lengthening amount and the percent increase (PI), 21 rabbits (acute lengthening) were divided into seven subgroups and 15 rabbits (gradual lengthening) into five subgroups. A nerve conduction study, light microscopic and electromicroscopic analysis of the sciatic nerve were performed.

Acute femoral lengthening between 0.5-0.75 cm (PI= 6-9%) caused remarkable electrophysiologic and microscopic changes in the sciatic nerve, gradual lengthening between 0.75-1.0 cm (PI= 9-13%) induced significant electrophysiologic changes, and gradual lengthening between 1.0-1.5 cm (PI=13-19%) caused significant pathologic change.

Gradual bone lengthening is safer for nerves than acute bone lengthing because of its safety margin, in terms of PI, is double that of acute bone lengthening. The results in this study provide helpful data to those in human nerve research upon the effects of acute and gradual bone lengthening.