Intraoperative spinal somatosensory evoked potential monitoring

The relationship of intraoperative monitoring of spinal cord somatosensory evoked potentials and postoperative deficit in 220 cases (121 with scoliosis, 41 with neoplasms, and 58 others) is reported. Bilateral posterior tibial nerve stimulation was used in 181 cases and unilateral median nerve stimulation in 39. Spinal cord (interspinous ligament needles), subcortical (neck surface), and cortical (scalp surface) SEP's were monitored. Seven patients had a worsening of neurological function after surgery, 3 of whom demonstrated significant changes in SEP's monitored. In an additional 4 cases, there was more than a 50% decrease in amplitude of subcortical/cortical SEP's during monitoring, but no change in neurological status postoperatively. Combined monitoring of spinal cord, subcortical, and cortical SEP's enhanced the certainty of detecting spinal cord dysfunction even though there was a significant number of false-negative and false-positive results. A marked change in the SEP's indicated a high chance of developing a neurological deficit (3 or 43% of 7 cases), and if there was no change the chance of any neurological postoperative deficits was extremely low (4 or 1.87% of 213 cases). These data justify the use of intraoperative SEP monitoring.