Utility of Motor Evoked Potentials to Diagnose and Reduce Lower Extremity Motor Nerve Root Injuries During 4,386 Extradural Posterior Lumbosacral Spine Procedures

Abstract BACKGROUND CONTEXT Motor evoked potentials (MEPs) have excellent sensitivity for monitoring the functional integrity of the lateral corticospinal tract of the spinal cord. The sensitivity for nerve root function, however, is not as well established; consequently, MEPs are often not utilized for posterior extradural spine procedures distal to the conus. Spontaneous electromyography (sEMG) and somatosensory evoked potentials (SSEPs) are often included for these procedures, but their limited sensitivity has been well documented. Given the risk of motor nerve root injuries during spine procedures, and specifically increased vulnerability of the L4 and L5 nerves, the sensitivity of MEPs was evaluated for diagnostic accuracy and therapeutic impact. PURPOSE To determine the diagnostic sensitivity of MEPs during lumbosacral spine procedures and the potential therapeutic impact of the resolution of MEP alerts. STUDY DESIGN A total of 4,386 posterior extradural lumbosacral spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) with sEMG, SSEPs, and MEPs were abstracted from a multi-institutional database. All cases took place between October 2015 and October 2017. No external funding was provided. OUTCOME MEASURES Sensitivity and specificity, as well as positive and negative likelihood ratios for new postoperative neurologic deficits were calculated for each modality individually as well as when combined (multimodality). PATIENT SAMPLE Age 18 and older METHODS Data entered in the electronic medical record were analyzed. Alerts to sEMG activity, decreases in SSEP amplitude, or decreases in MEP amplitude were documented as well as the status of the alerts at closure: resolved or unresolved. The presence of an sEMG alert or an unresolved MEP or SSEP alert at closure was considered a positive diagnostic result, and these results were assessed relative to presence of new immediate onset neurologic deficits as documented in the electronic record. RESULTS The sensitivity and specificity of multimodality IONM for new immediate-onset lower extremity motor deficits were 100.0% (95% CI: [64.6, 100.0]) and 92.2% [91.1, 93.1], respectively. Looking at the modalities in isolation, the sensitivity of MEPs was considerably better than either lower extremity sEMG or posterior tibial nerve SSEPs: 100.0% [78.5, 100.0] versus just 14.3% [4.0, 39.9] and 28.6% [8.2, 64.1], respectively. Surprisingly, the specificity of lower extremity MEPs was better than sEMG, 97.9% [97.5, 98.3] versus 95.4% [94.7, 96.0] (χ2= 43.0, p CONCLUSIONS The diagnostic accuracy of MEPs for anterior tibialis-related nerve root dysfunction supports the inclusion of this modality during routine posterior extradural lumbosacral procedures, especially when the L4 or L5 nerve roots are at risk. Moreover, therapeutic interventions that lead to the resolution of MEP alerts averts postoperative neurologic injuries.