Threshold-Anchored Mechanomyography Metrics for Patient Stratification in Spinal Decompression: Associations with...

Background/Objectives: Spinal decompression surgery shows variable outcomes, with reoperation rates up to 37.5%. Surgeons lack objective intraoperative tools to assess decompression adequacy. Mechanomyography (MMG) measures nerve excitability through mechanical muscle responses to electrical stimulation. While compressed nerves require higher stimulation thresholds, optimal quantification approaches remain undefined. We explored associations between intraoperative MMG threshold changes and six-week pain outcomes, comparing metrics anchored to a 2.0 mA reference threshold versus percentage-based measures. Methods: Prospective exploratory pilot study of 42 patients (112 nerves) undergoing lumbar or cervical decompression. MMG thresholds were recorded pre- and post-decompression. Numeric Pain Scale scores were obtained preoperatively and at six weeks. Three metrics were compared: percentage change, Threshold Reduction Ratio (TRR; measuring proportion of threshold elevation above 2.0 mA eliminated by decompression), and Threshold Excess (TE; residual threshold remaining above 2.0 mA), with TRR and TE anchored to 2.0 mA based on published normal ranges. Results: Among 40 patients with baseline pain, threshold-anchored metrics showed substantially stronger correlations with pain improvement than percentage-based measures (TRR: r = 0.656, p < 0.001 vs. percentage: r = 0.397, p = 0.011). Threshold Excess was associated with a linear dose-response: each 1 mA above 2.0 mA corresponded to 6.3% less pain improvement (p = 0.001). Patients achieving ≤2.0 mA had 6.1-fold increased odds of complete pain relief versus those above 2.0 mA (76.5% vs. 34.8%, p = 0.013). Internal leave-one-out cross-validation suggested internal stability (TRR shrinkage ≈ 9.3%; TE's dose-response slope remained stable). Conclusions: In this exploratory pilot study, threshold-anchored MMG metrics (TRR and TE) showed stronger correlations with early pain outcomes than percentage-based measures. These exploratory findings require external validation in independent cohorts before clinical implementation. If validated prospectively, these metrics could provide objective, real-time feedback for clinical interpretation to inform surgical decision-making during spinal decompression, enabling surgeons to tailor decompression to individual physiology rather than relying on standardized anatomical criteria. Future work should explore patient-specific threshold targets that account for age, chronicity, and comorbidities.