Intraoperative MEP and EMG during the wake-up phase as adjuncts to the wake-up test in severe spinal deformity surgery

Background This study aimed to evaluate the adjunctive value of intraoperative motor evoked potential (MEP) recovery and electromyographic (EMG) activity during the wake-up phase in predicting postoperative neurological outcomes in high-risk patients with intraoperative MEP alerts during severe spinal deformity surgery. Methods A retrospective analysis was conducted in 111 patients with intraoperative MEP alerts who underwent thoracic osteotomy for severe spinal deformity between 2008 and 2022. Postoperative neurological outcomes were compared according to wake-up test responses, MEP recovery, and EMG activity during the wake-up phase. The predictive performance of each modality and their combinations for immediate postoperative complete lower-limb paralysis was assessed. The time required to obtain interpretable intraoperative responses during the wake-up phase was also analyzed. Results Among 59 patients without immediate postoperative complete lower-limb paralysis, 46 (78.0%) recovered motor function immediately after surgery, and all recovered within 1 month. Among 52 patients with immediate postoperative complete lower-limb paralysis, 18 (34.6%) recovered within 1 month, 47 (90.4%) recovered within 1 year, and 5 (9.6%) failed to return to baseline neurological status by final follow-up. The false-positive rate for predicting complete paralysis was 20.3% for the wake-up test alone, 10.2% for MEP recovery alone, and 33.9% for EMG alone. This rate decreased to 6.8% when MEP and EMG were combined, and to 0% when wake-up test, MEP, and EMG findings were considered together. In patients without complete paralysis, MEP and EMG responses were obtained earlier during arousal than direct wake-up test responses. Conclusions In high-risk severe spinal deformity cases with intraoperative MEP alerts, MEP recovery and EMG activity during the wake-up phase may provide useful complementary information to the traditional wake-up test for assessing postoperative neurological risk. A multimodal intraoperative assessment strategy may improve the interpretation of neurological status during arousal and help reduce false-positive findings in selected patients.