Wednesday, September 26, 2018 9:00 AM – 10:00 AM Best Papers: 6. Diagnostic accuracy and clinical impact of motor evoked potential (MEP) monitoring during 4,425 posterior extradural lumbosacral procedures involving the L5 vertebra

Abstract

BACKGROUND CONTEXT The value of intraoperative neuromonitoring (IONM) is predicated on accurate diagnostic information and the clinical impact is contingent on effective action. Spontaneous electromyography (sEMG) and somatosensory evoked potentials (SSEPs) have known limitations in diagnosing spinal nerve root motor dysfunction. In this study, we assessed the diagnostic accuracy and utility of MEPs during lumbosacral procedures in which there is elevated risk of L5 nerve root injury and consequent foot drop. STUDY DESIGN/SETTING Posterior lumbosacral procedures involving the L5 vertebral level and monitored with MEPs, in mixed combination with sEMG and SSEPs, from October 2015 to October 2017 were reviewed retrospectively from a multi-institutional IONM database. Procedures involving thoracic levels, a lateral or oblique approach, pediatrics, tumors, or tethered cords were excluded. The diagnostic results of MEPs, sEMG, and SSEPs were calculated with respect to motor neurologic outcome in the immediate postoperative period. Positive diagnostic results were defined as unresolved SSEP or MEP alerts or episodes of sEMG reported to the surgeon. Fully resolved SSEP or MEP alerts, or no IONM alerts, were negative results. Deficit rates, sensitivities and specificities were calculated together with 95% Wilson confidence intervals (CIs); odds of new motor deficit were calculated using small-sample correction and Wald 95% CIs. In addition, the actions prompted by alerts were reviewed and grossly categorized as either (A) active surgical and/or pharmacological/physiological intervention, (B) patient repositioning, or (C) surgical pause. RESULTS There were 16 new onset motor deficits in 4,425 procedures (0.36%, Wilson 95% CI: [0.22, 0.59]). The sensitivity of MEPs was 93.8% [71.7, 99.7]. The sensitivities of sEMG and SSEPs were much lower, 18.8% [6.6, 43.0] and 37.5% [13.7, 69.4] respectively. MEP specificity was 97.2% [96.6, 97.6]. For unresolved MEP alerts (n=139), the rate of new motor deficit was 10.8% [6.6, 17.0]; relative to procedures with no alerts or fully resolved alerts, the odds of a new motor deficit were significantly increased (OR=257.1, Wald 95% CI: [65.9, 1918.8], p CONCLUSIONS MEPs have excellent diagnostic accuracy during lumbosacral procedures involving the L5 vertebra. Unresolved TA MEP alerts are associated with a high incidence of foot drop injuries, but the resolution of MEP alerts has a demonstrable positive clinical impact. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.