Prospective evaluation of mechanomyography versus triggered electromyography for intraoperative assessment of cortical breaches during instrumented lumbar surgery

Introduction Pedicle screws are essential in spinal arthrodesis surgeries but pose potential risks due to their proximity to neural and vascular structures. Traditionally, tEMG has been used to assess screw placement, though its invasiveness, low specificity, and cost limit its applicability. MMG may offer a promising alternative for routine clinical use. Our study compares the relative accuracy of triggered electromyography (tEMG) versus mechanomyography (MMG) in detecting intraoperative cortical bony breaches. Methods Using an equivalence trial design, consecutive patients undergoing posterior lumbosacral spinal arthrodesis were prospectively enrolled at a single institution. Pedicle screw trajectories were queried in real-time using combined tEMG and MMG-based evaluations at pretap, tap, post-tap and postscrew placement stages. Intraoperative computed tomography (CT) scans were performed to evaluate pedicle screw trajectories according to the Gertzbein-Robbins (GR) classification. Receiver operating characteristic curve analysis were performed to evaluate the relative accuracy of tEMG and MMG threshold potentials to detect cortical breaches. Pain and quality-of-life outcomes were evaluated up to 3 months postoperatively. Results A total of 303 consecutive lumbar pedicle screw trajectories were included (61 participants; mean age: 61.3 ± 9.7 years; male-to-female ratio: 32:29). 7 grade C-E GR cortical breaches were identified in a total of 5 subjects, with 5 (71.4%) classified as Grade C and 2 (28.6%) as Grade E. Baseline demographics were comparable between the breach and nonbreach groups. The tEMG and MMG AUC values determining predictive ability for breach detection were comparable for the pretap (AUC 0.82 vs. 0.80, p = .442) and post-tap stages (AUC 0.71 vs. 0.79, p = .380). Follow-up pain and functional assessments revealed significant improvements at last follow-up. Conclusion tEMG and MMG demonstrate high and equivalent accuracy to detect cortical breaches intraoperatively. Adequate utilization of either technique may enhance pedicle screw placement accuracy, reducing intraoperative complications and improving surgical outcomes.