Changes in somatosensory-evoked potentials in limb lengthening. An experimental study on rabbits' tibiae.

To assess the influence of the rate and amount of distraction on the electrophysiologic function of the peripheral nerve during limb lengthening, somatosensory-evoked potential (SSEP) studies were performed on the hindlimbs of 96 rabbits. In Group I, the tibiae were lengthened 0.35 mm per day; in Group II, 0.7 mm per day; in Group III, 1.05 mm per day; and in Group IV, 1.4 mm per day. The studies were done preoperatively and then postoperatively, until six weeks in Group I, five weeks in Group II, four weeks in Group III, and three weeks in Group IV. As lengthening proceeded, the P1 (the first major positive peak) latency gradually increased, whereas the amplitude decreased. Significant amplitude changes were observed at six-weeks postsurgery in Group I, three weeks in Group II, two weeks in Group III, and one week in Group IV. Significant changes in P1 latency were observed at four weeks postsurgery in Group II, three weeks in Group III, and two weeks in Group IV. Greater percentage increases in tibial length corresponded to more marked changes in P1 latency and amplitude. The SSEP monitoring may serve as an effective tool for early detection of neurologic dysfunction during limb lengthening.