The Frequency of Motor Evoked Potential Alerts During Lumbar Spinal Surgeries

Abstract

Background: Spinal surgery is associated with a high rate of neurological sequelae due to damage to the spinal nerve roots. This study aims to determine the most common alert type during lumbar spinal surgeries, including either anesthetic/physiological, positioning, or surgical.

Methods: We retrospectively reviewed 1,159 extradural spinal surgeries with intraoperative neurophysiological monitoring (IONM) from January 2019 to March 2021 to evaluate the incidence of events. We analyzed the Motor Evoked Potentials (MEP) alerts and changes in the neurophysiological signals. Cases were categorized by procedure type, muscles, and then by the level (upper; or lower) that the MEP alert occurred.

Results: 131 of 1159 (11.3%) surgeries had an intraoperative MEP alert (55% female and 45% males). An MEP alert occurred with a possible risk of post-operative deficit, and 56% of those MEP alerts were due to anesthesia/pharmacological intervention. 50 of the 131 cases had multiple muscle group alerts. Of the five muscle groups we reviewed, quadriceps were most likely to cause an alert. However, the tibialis anterior is most at risk as loss of MEP to this muscle could lead to foot drop. Twenty-seven of the 131 cases had MEP alerts resolved intraoperatively by either repositioning, adjustment in anesthesia, or surgical action. Pre-existing conditions were not considered in this study. The MEP had a greater incidence than somatosensory evoked potentials (SSEP) and electromyography (EMG) in detecting intraoperative and postoperative neurological deficits, especially those involving a single nerve root.

Conclusion: During extradural lumbar procedures, MEPs provide accuracy to be required as a modality as SSEP and s-EMG lack the sensitivity that could lead to false negatives. MEPs allow for prompt, timely investigation, and initiation of intervention by the surgical team to mitigate the possible deficit. Though MEPs could lead to false positive alerts, this can be easily adjusted by correcting alert criteria. Utilization of a multimodal intraoperative neuromonitoring intervention avoided postoperative neurologic deficits in most cases. Our data shows that the overall incidence of MEP is higher in detecting nerve root injuries during lumbar spine surgeries than in SSEP and EMG. We recommend adding the MEP modality to the multimodality IONM protocol for all lumbar surgeries to minimize nerve root injuries and postoperative deficits.