Pattern-specific changes and discordant prognostic values of individual leg-muscle motor evoked potentials during spinal surgery

ObjectiveThe aim of the study is to evaluate the efficacy of muscle motor evoked potentials (mMEPs) in individual leg muscles for spinal surgery monitoring.MethodsData were obtained from 209 patients who underwent spine surgery with intra-operative mMEP monitoring in the tibialis anterior (TA) and abductor hallucis (AH) muscles. The mMEP generation, pattern-specific mMEP loss and recovery, and the accuracy of individual mMEP changes in predicting postoperative motor deficit were assessed.ResultsGeneration rate of mMEPs was higher in the AH than in the TA (p < 0.001). The mMEP in the TA was more sensitive in detecting mMEP loss than in the AH (p < 0.001); however, mMEP in the AH was more sensitive in detecting mMEP recovery (p < 0.001). The mMEPs in the TA had high sensitivity in predicting sustained postoperative motor deficits. By contrast, mMEPs in the AH showed a high positive predictive value.ConclusionsAlthough mMEPs were generated at a high rate in the AH, mMEP in the TA can play an important complementary role in intra-operative mMEP monitoring, because mMEP in the TA can be more sensitive to potential neural damage.SignificanceUsing a combination of muscles with individual sensitivities and clinical significances will improve intra-operative mMEP monitoring strategies.

► Muscle motor evoked potentials (mMEPs) were generated at a high rate in the abductor hallucis (AH) and had high positive predictive values for sustained postoperative motor deficits. ► However, mMEPs in the tibialis anterior were more sensitive in detecting perioperative neural damage and in predicting sustained postoperative motor deficits than mMEPs in the AH. ► The interpretations of intra-operative mMEPs should be individualised according to the type of muscles recorded, and a tailored approach using multi-muscle recordings may contribute to better outcomes for spinal surgery.