Investigation of the Relationship Between Intraoperative Transcranial Motor Evoked Potential and Compound Muscle Action Potential in Corrective Spinal Deformity Surgery.

OBJECTIVE: This study aimed to evaluate the relationship between transcranial motor-evoked potentials (Tc-MEPs) and compound muscle action potentials (CMAPs) during spinal deformity correction surgery and to assess the clinical utility of their simultaneous evaluation. METHODS: We retrospectively analyzed 42 patients who underwent spinal deformity correction surgery and had reliable Tc-MEP and CMAP recordings available for correlation analysis. CMAPs were recorded from the median nerve after supramaximal stimulation, whereas Tc-MEPs were recorded from six target muscles. Correlation analyses of percentage changes in Tc-MEP and CMAP amplitudes were performed across three phase comparisons using four intraoperative measurement time points. RESULTS: Significant positive correlations between CMAP and Tc-MEP amplitudes were observed mainly in the abductor pollicis brevis and abductor hallucis muscles at multiple surgical phases, whereas no consistent correlation was observed in the tibialis anterior muscle. Overall, these correlations were small to moderate. In three patients, Tc-MEP amplitude decreased by ≥ 70% during scoliosis correction. In one case, CMAP amplitude remained preserved despite marked Tc-MEP reduction, whereas in the other two cases, both Tc-MEP and CMAP amplitudes decreased simultaneously. All patients recovered after intraoperative intervention, and no postoperative neurological deficits were observed. These findings suggest that simultaneous evaluation of Tc-MEP and CMAP may provide complementary information for interpreting intraoperative waveform changes. CONCLUSIONS: Small-to-moderate correlations were observed between Tc-MEP and CMAP amplitudes during spinal deformity correction surgery. Although the strength of these correlations was limited, simultaneous evaluation of Tc-MEP and CMAP may aid interpretation of intraoperative Tc-MEP amplitude reductions and may represent a practical strategy for improving intraoperative decision-making.