Somatosensory evoked potential evaluation of acute nerve injury associated with external fixation procedures

The effects of different mechanisms of acute nerve injury on peripheral nerve function during K wire application and 1 stage limb lengthening were evaluated prospectively in 24 goats using somatosensory evoked potentials. Stable somatosensory evoked potential recordings throughout 3-day experiments were obtained in animals with wires placed at a distance from or directly adjacent to a nerve but without producing any tension or pressure. Complete loss of the peroneal nerve somatosensory evoked potentials occurred if this nerve was perforated by wire, underwent excessive pressure by wire, or had been over-stretched due to acute 10% limb lengthening. Acute distraction resulted only in peroneal nerve dysfunction, while the tibial nerve was relatively unaffected. Although somatosensory evoked potential changes were not specific for the type of injury produced and the time of waveform disappearance varied, significant somatosensory evoked potential changes (> 50% amplitude reduction, > 10% latency delay or both) were seen within the first 15 minutes after injury in 90% of the cases. The somatosensory evoked potential changes did not reverse if the offending wire or distraction was left in place for the full duration of the experiment. Variable nerve conduction recovery was observed in all animals who had the insult removed immediately after the somatosensory evoked potentials disappearance. The greatest improvement occurred after discontinuation of nerve distraction. The worst somatosensory evoked potential waveform recovery was noted in animals with nerve perforation. Intraoperative somatosensory evoked potential monitoring proved to be a reliable and useful technique for earlier detection of acute nerve injury during external fixation procedures.