Spinal cord monitoring during posterior spinal instrumentation and fusion

Two hundred seventy-five consecutive patients who were treated by posterior spinal instrumentation and fusion with iliac crest bone graft were intraoperatively monitored using cortical somatosensory-evoked potentials without a planned wake-up test. The monitoring was performed using a TECA TE-4 system that included an electromyograph, a nerve stimulator, and a digital averager. Intraoperatively, six patients (2%) demonstrated significant changes in evoked potentials, consisting of either marked increase in latency or a loss of wave form during instrumentation of the spine. The instrumentation was removed immediately and the evoked potentials returned to base-line tracing within 15-30 minutes in all six cases. Five patients who had instruments refitted to maintain a lesser amount of correction had no subsequent change in the evoked potentials. One patient had spinal fusion without instrumentation. Postoperatively, all patients are neurologically normal.