A Modified Method of Triggered Electromyography Monitoring in Minimally Invasive Spine Surgery: Comparison to Conventional Techniques and Correlation with Body Mass Index.

Purpose: Conventional triggered electromyography (EMG) in percutaneous pedicle screw (PPS) systems may be unreliable due to the interaction between the insertion apparatus and patient's soft tissue. Our aim was 1) to describe a modified technique of triggered EMG monitoring using insulated Kirschner wire (K-wires), 2) to compare EMG potentials with conventional techniques, and 3) to demonstrate the relationship between patient body mass index (BMI) and triggered EMG potentials.

Methods: This was a prospective cross-sectional study of 50 patients undergoing minimally invasive PPS placement. Triggered EMG measurements using K-wires before and after insulation were compared. The difference between EMG measurements before and after insulation was correlated with patient BMI.

Results: A total of 50 patients, 22 females and 28 males, underwent triggered EMG testing using K-wires prior to final PPS placement in the thoracic and lumbosacral spine for a total of 472 triggered EMG measurements. When compared to standard triggered EMG monitoring, insulated triggered EMG monitoring demonstrated an average 55.4% decrease in EMG values (P < 0.001). Increasing BMI correlated to increasing % decrease in EMG values (r-coefficient, 0.376; P < 0.01).

Conclusions: We describe a cost-effective, efficient, and reliable technique for triggered EMG during PPS placement which may help ensure accurate screw placement and minimize potentially devastating complications.