Intraoperative SSEP monitoring during external fixation procedures in the lower extremities

The efficacy of somatosensory evoked potentials (SSEPs) to detect acute peripheral nerve injury during external-fixator application in the lower extremities was evaluated in 40 children with 42 Ilizarov surgical procedures. The study included patients who were either clinically normal or who had preexisting neuropathy but consistent and reliable SSEP responses preoperatively. SSEPs were recorded from the popliteal fossa and lumbar regions after alternating stimulation of the peroneal and posterior tibial nerves at the ankle. SSEP changes due to anesthesia, Ilizarov apparatus application, and other intraoperative variables are described. Significant deterioration or total loss of SSEP response during surgery occurred in four cases. Two of these patients were normal preoperatively and had symptoms of neurologic deficit postoperatively; the other two had exacerbations of pre-existing neuropathy. In general, the peroneal nerve was at greater risk for injury during surgery. SSEP monitoring proved to be technically feasible in external-fixation procedures on the lower extremities and may be a practical tool for detection of intraoperative nerve compromise.