Electrode Placement During Stimulus Evoked Electromyographic Monitoring of Iliosacral Screw Insertion: A Finite Element Model

Stimulus evoked electromyography is currently used during surgery to prevent nerve root injury during iliosacral screw insertion. In order to evaluate the importance of anode location in this procedure, a three dimensional finite element model was constructed from computed tomography data to evaluate the effectiveness of five electrode locations. Three anode locations (CASIS, dorsal midline and ventral midline) performed well, including the one most commonly used clinically (ventral midline). The dorsal midline, ventral midline, and CASIS anode locations provide data on the proximity to the neural structure in the superior, inferior and contralateral directions respectively that were attenuated at other anode locations. Modification of the technique to include monitoring of multiple anode locations could further reduce the incidence of injury