Can We Expect a Favorable Postoperative Neurological Outcome Through the Intraoperative Deteriorated MEP Recovery for Cervical Spinal OPLL Surgery?

BACKGROUND AND OBJECTIVES: Intraoperative motor evoked potential (MEP) monitoring is widely used during cervical ossification of the posterior longitudinal ligament (OPLL) surgery, yet the clinical significance of intraoperative MEP deterioration remains controversial. This study investigated whether early neurological outcome is more closely associated with the degree of MEP recovery after deterioration rather than with the magnitude of the deterioration itself and whether this relationship differs according to surgical approach. METHODS: We retrospectively reviewed 164 patients who underwent cervical OPLL surgery at a single center between 2018 and 2024. Among them, 27 patients (19 anterior and 8 posterior approaches) who experienced intraoperative MEP deterioration were included. MEP amplitudes were normalized to baseline and evaluated at 4 time points: baseline, MEP deterioration during decompression or instrumentation, MEP recovery following corrective intraoperative maneuvers, and the end of surgery. Early postoperative neurological outcome was assessed using the change in Frankel grade. Correlation analyses, linear regression, receiver operating characteristic analyses, and subgroup analyses by surgical approach were performed. RESULTS: Recovery-based MEP metrics evoked potential recovery (EP rec ) demonstrated stronger associations with early neurological outcome than deterioration-based metrics. EP rec showed the strongest correlation with outcome (Spearman ρ = 0. 590, 95% CI 0.296-0.803, P < .001), whereas the magnitude of intraoperative deterioration alone was not significantly associated with outcome. Receiver operating characteristic analysis suggested that EP rec may have discriminative potential for early neurological deterioration (area under the curve = 0.854, 95% CI 0.674-0.969); however, no reliable cutoff could be identified. In the anterior approach group, favorable neurological outcomes were observed despite a smaller degree of MEP recovery, although this trend did not reach statistical significance. CONCLUSION: In cervical OPLL surgery with intraoperative MEP deterioration, recovery-based MEP metrics are more closely associated with early postoperative neurological outcome than deterioration-based measures. This supports a recovery-centered framework for interpreting intraoperative MEP changes, warranting further validation in larger studies.