Friday, September 28, 2018 1:00 PM–2:30 PM abstracts: achieving lumbar interbody fusion: 199. Use of motor evoked potentials during lateral lumbar interbody fusion reduces postoperative deficits

Abstract

BACKGROUND CONTEXT Intraoperative neurophysiological monitoring (IONM) has gained rather wide-spread acceptance as a method to mitigate risk to the lumbar plexus during Lateral Lumbar Interbody Fusion (LLIF) surgery. The most common approach to IONM involves using only electromyography (EMG) monitoring, and the rate of postoperative deficit remains unacceptably high. Other test modalities, such as transcranial electric motor-evoked potentials (tcMEPs) and somatosensory-evoked potentials (SSEPs), may be more suitable for monitoring neural integrity but they have not been widely adopted during LLIF. Recent studies have begun to examine their utility in monitoring LLIF surgery with favorable results. PURPOSE To evaluate the efficacy of different IONM paradigms in the prevention of iatrogenic neurologic sequelae during LLIFand to specifically evaluate the utility of including tcMEPs in an IONM strategy for LLIF surgery. STUDY DESIGN/SETTING Nonrandomized, retrospective analysis of 479 LLIF procedures at a single institution over a 4-year period. During the study epoch, three different IONM strategies were employed for LLIF procedures: (1) Surgeon-directed T-EMG monitoring (“SD-EMG”), (2) neurophysiologist-controlled T-EMG monitoring (“NC-EMG”), and (3) neurophysiologist-controlled T-EMG monitoring supplemented with MEP monitoring (“NC-MEP”). PATIENT SAMPLE The patient population was comprised of 254 males (53.5%) and 221 females (46.5%). Patient age ranged from a minimum of 21 years to a maximum of 89 years, with a mean of 56.6 years. OUTCOME MEASURES Physician-documented physiologic measures included manual muscle test (MMT) grading of hip-flexion, hip-adduction, or knee-extension, as well as hypo- or hyperesthesia of the groin and/or anterolateral thigh on the surgical side. Self-reported measures included numbness or tingling in the groin and/or anterolateral thigh on the surgical side. METHODS Patient progress notes were reviewed from the postoperative period up to 12 months after surgery. The rates of postoperative sensory and/or motor deficit consistent with lumbar plexopathy or peripheral nerve palsy on the surgical side were compared between the three cohorts. RESULTS Using the dependent measure of neurologic deficit, whether motor and/or sensory, patients with NC-MEP monitoring had the lowest rate of immediate postoperative deficit (22.3%), compared to NC-EMG monitoring (37.1%) and SD-EMG monitoring (40.4%). This result extended to sensory deficits consistent with lumbar plexopathy (pure motor deficits being excluded); patients with NC-MEP monitoring had the lowest rate (20.5%) compared to NC-EMG monitoring (34.3%) and SD-EMG monitoring (36.9%). Additionally, evaluation of postoperative motor deficits consistent with peripheral nerve palsy (pure sensory deficits being excluded), the NC-MEP group had the lowest rate (5.7%) of motor deficit compared to the SD-EMG (17.0%) and NC-EMG (17.1%) cohorts. Finally, when assessing only those patients whose last follow-up was greater than or equal to 12 months (n=251), the rate of unresolved motor deficits was significantly lower in the NC-MEP group (0.9%), as compared to NC-EMG (6.9%) and SD-EMG (11.0%). Comparison of the NC-MEP versus NC-EMG and SD-EMG groups, both independently and combined, was statistically significant (>95% confidence level) for all analyses. CONCLUSIONS The results of the present study indicate that preservation of tcMEPs from the adductor longus, quadriceps, and tibialis anterior muscles are of paramount importance for limiting iatrogenic sensory and motor injuries during LLIF surgery. In this regard, the inclusion of tcMEPs serves to compliment EMG and allows for the periodic, functional assessment of at-risk nerves during these procedures. Thus, tcMEPs appear to be the most effective modality for the prevention of both transient and permanent neurologic injury during LLIF surgery. We propose that the standard paradigm for protecting the nervous system during LLIF be adapted to include tcMEPs.