S120. Diagnostic accuracy and therapeutic impact of Motor Evoked Potentials (MEPs) during 5706 extradural lumbosacral procedures

Abstract

Introduction MEPs have excellent sensitivity for monitoring the functional integrity of the spinal cord during spine surgery. Their sensitivity to evolving plexus or nerve root injury, however, is not as well established; consequently, MEPs are often not utilized during surgery below the conus. Given the risk of anterior thigh weakness following lateral fusions and foot drop following prone procedures involving the L5 vertebra, MEPs were evaluated for their diagnostic accuracy and contribution to injury avoidance during these procedures. Methods Two cohorts were delineated from a multi-institutional database of lumbosacral surgeries monitored with MEPs from October-2015 to October-2017: 1281 procedures involved a lateral or oblique approach and 4425 posterior procedures involved the L5 vertebra. Procedures involving pediatrics, tethered cords, tumors, or thoracic levels were excluded. Diagnostic accuracy at closure was assessed relative to changes in immediate postoperative motor function. Confidence intervals (CIs) for deficit rate, sensitivity and specificity were calculated using the Wilson method. Relative odds of deficit by IONM alert status were calculated using small-sample correction and Wald 95% CIs. Results The sensitivity and specificity of MEPs in lateral/oblique procedures was 77.8% [45.3, 93.7] and 97.0% [95.9, 97.8], respectively. The overall rate of new motor deficit was 0.7% (9/1281, [0.4, 1.3]). For procedures with unresolved MEP alerts the deficit rate was 15.6% (7/45, [7.7, 28.8]) and, relative to procedures with no alerts or fully resolved alerts, the odds of a new motor deficit were significantly increased (OR = 73.8, [22.2, 417.1], p Conclusion The diagnostic accuracy of MEPs for nerve root and plexus motor function justifies their usage during extradura lumbosacral procedures; moreover, the decrease in morbidity associated with the resolution of MEP alerts points to their value in prompting corrective action in the face of evolving neurologic injury.