Electrophysiologic evaluation of neuromuscular functions during limb lengthening by callus distraction.

We investigated the effects of different rates and extents of lengthening on the affected nerves and muscles in callus distraction, in a rabbit tibial model. Electrophysiologic evaluations measuring the motor nerve conduction velocity of the peroneal and tibial nerves, and compound muscle action potentials of the anterior tibialis and gastrocnemius muscle were performed sequentially on rabbits whose left legs were lengthened at different rates and to different extents over a 5-month period after surgery. We found that neuropathies of the peroneal nerves developed earlier and were more severe than those of tibial nerves, especially when the rate of lengthening was over 2 mm per day, or when the extent of lengthening was over 20% of the leg length at a lengthening rate of 1 mm per day. When the nerve damage was mild, there was a slow recovery of nerve function with time. The anterior tibialis muscle exhibited earlier and more severe damage than the gastrocnemius muscle during lengthening, especially when the rate of lengthening was over 2 mm per day, or when the extent of lengthening was over 20% of leg length. Elevated serum creatine kinase levels also indicated muscle damage after lengthening, especially in cases of high lengthening rates and long extent of lengthening. We conclude that nerves and muscles may have the same optimal rate of lengthening as bones, (1 mm per day). However, the extent of lengthening still has a limit of 20% or less of the total leg length. Electrophysiologic evaluation measuring the motor nerve conduction velocity and compound muscle action potential can serve as a tool for early detection and for long-term monitoring of neurologic dysfunction.