Intraoperative Stimulus-Evoked Electromyographic Monitoring for Placement of Iliosacral Implants: An Animal Model

Objective: A canine model was designed to evaluate the feasibility of stimulus-evoked electromyographic (EMG) monitoring of the lumbosacral nerve roots during the insertion of iliosacral implants. Study Design/Methods: Four 2.5-millimeter Kirschner wires (K-wires) were percutaneously inserted under general anesthesia into the S1 body of each of five dog hemipelves using C-arm fluoroscopy image-intensifier control in an actual attempt to compromise the S1 canal and the S1 nerve root. A searching current of twenty milliamperes was initially applied to the K-wire with monitoring electrodes placed in the gastrocnemius muscle. Current thresholds required to evoke an EMG response were recorded for each K-wire. Actual K-wire location was determined by anatomical dissection. Results: Evaluation of these twenty wires revealed that current threshold was directly related to the proximity of the K-wire to the nerve root, with a correlation coefficient of 0.94 (p < 0.001). Conclusions: Stimulus-evoked EMG monitoring provided reliable data indicating the proximity of the iliosacral implants to the sacral nerve root. This method of intraoperative nerve monitoring could potentially decrease the risk of iatrogenic nerve root injury during pelvic ring surgery. Further study is warranted.