Analysis of Intraoperative Neuromonitoring Events During Spinal Corrective Surgery for Idiopathic Scoliosis

Study design: Multicenter review of prospectively collected data.

Objective: To determine the frequency and outcome of intraoperative neuromonitoring (IONM) alerts during surgical correction of idiopathic scoliosis (IS).

Summary of background data: Providing corrective action after identifying IONM events will ideally prevent neurologic complication.

Methods: Prospectively gathered clinical data and IONM reports recorded during spinal surgery for IS were analyzed. Patients were divided into 2 groups: those with clear IONM changes and those with no IONM events. A neuromonitoring event was defined as a change from baseline transcranial motor evoked potentials or somatosensory evoked potentials in the lower extremities. The risk, rate, cause, and outcome of each neuromonitoring alert were assessed.

Results: A total of 579 IS cases were analyzed. Twenty-one cases (3.6%) had an IONM event. In 18 of the 21 cases (86%), the potentials returned to baseline after corrective action. Of the 3 with remaining abnormalities, 2 (0.3%) awoke with deficits (1 unilateral weakness and 1 unilateral sensory change). In 12 cases, the changes were thought to result from low blood pressure; all responded to elevation of the mean arterial pressure. Five changes were associated with misplaced screws (in 4, the monitoring returned after removal or redirection; all 5 were normal postoperatively). Traction was the cause in 2 cases, both of which responded to reduction in traction. In 4 cases, the cause was unclear. Two remained abnormal and awoke with neurologic deficit. There were no postoperative neurologic deficits in any cases with normal neuromonitoring. Surgical time (416 vs. 291 minutes; p < .001) and percent estimated blood volume lost (64% ± 47% vs. 31% ± 26%; p < .001) were significantly increased in cases in which intraoperative events were observed.

Conclusions: The rate of neuromonitoring changes was 3.6% when using both transcranial motor evoked potential and somatosensory evoked potential monitoring. When a cause was identified and corrective action was taken, there were no postoperative neurologic deficits.