T91. Factors predicting the successful generation of baseline motor evoked potentials in patients undergoing spine surgery

Introduction The purpose of this study was to search for clinical factors predicting the successful generation of baseline muscle motor evoked potentials (mMEPs) in patients undergoing spine surgery and to determine the relationship with postoperative functional outcome. Methods From July 2014 to June 2015, a total of 345 patients underwent spine surgery with intraoperative mMEPs monitoring and were consecutively included in this study. Their demographic features, clinical parameters, and mMEPs recording results were reviewed retrospectively. Results Two hundred and fifty-three (73%) patients showed the successful generation of baseline mMEPs at all recording muscles, and 92 (27%) patients failed to record baseline mMEPs at one or more limb muscles. When we compared the preoperative clinical parameters of the two groups, the latter group (“Failure group”) significantly had a higher male ratio, lower MRC grades, higher Nurick grades, more often cervical/cervicothoracic segment involvement, higher proportion of the presence of spine surgery history, motor deficits, sensory symptoms, bladder/bowel dysfunction, T2-weighted high signal intensity (HSI) of cord at spine MRI compared to the former group (“Success group”) and were older. Among these factors, male sex, cervical/cervicothoracic lesion location the presence of T2-weighted HSI of cord, preoperative Nurick grade, and MRC grade showed a significant contribution for predicting the successful generation of mMEPs. When analyzing predictors for postoperative poor functional outcomes, the success rate of mMEPs recording and lesion etiology were significantly related factors for the aggravation of the Nurick grades before and after surgery. Conclusion Various clinical parameters including lesion location, abnormal cord signal on MRI, preoperative motor power, and functional status were revealed to have a significant relationship with the successful generation of baseline mMEPs. Additionally, the successful generation of mMEPs was one of the indicators for predicting the long-term functional outcome.