Intraoperative electromyographic monitoring to optimize safe lumbar pedicle screw placement – a retrospective analysis

BACKGROUND The foremost concern of a surgeon during pedicle screw fixation is safety. Assistive modalities, especially intraoperative electromyographic monitoring (EMG) can function as an essential tool to recognize screw malposition that compromise neural integrity, so that the screws can be repositioned immediately rather than later. We intend to study the efficacy of intraoperative EMG monitoring to detect potential pedicle breach and evaluate whether reoperation rates were significantly reduced. METHODS Retrospectively, patients who underwent posterior stabilization with pedicle screws for various pathologies were analysed and those with screws among L1-S1 levels were shortlisted. They were divided into two groups. Group 1 included patients in whom trigger EMG (t-EMG) was used to confirm appropriate screw placement and Group 2 included those in whom it was not used. Responses to t-EMG and corresponding stimulation thresholds were recorded for Group 1 patients. The sensitivity and specificity of the test was calculated. Reoperation rates due to postoperative neurologic compromise caused by malpositioned screws were compared between both the groups. RESULTS A total of 518 patients had 3112 pedicle screws between L1-S1 levels. Among Group 1 [n = 296; Screws = 1856], 145 screws (7.8%) showed a positive response for t-EMG at stimulation thresholds ranging between 2.6 to 19.8 mA. The sensitivity and specificity of t-EMG to diagnose potential pedicle breach was found to be 93.33% and 92.88% respectively. Only one patient among Group 1 required reoperation. However, among Group 2 [n = 222; screws = 1256], six patients required reoperation. This indicated a significant decrease in the number of malpositioned screws that caused neurological compromise [p = 0.02], leading to subsequent decrease in reoperation rates [p = 0.04] among Group 1 patients. CONCLUSIONS Trigger EMG is well efficient in detecting potential pedicle screw breaches that might endanger neural integrity. In combination with palpatory and radiographic assessment, it will certainly aid safe and secure pedicle screw placement. It can also efficiently reduce reoperation rates due to neurologic compromise provoked by a malpositioned screw.