Intraoperative Neuromonitoring Changes During MIS-TLIF Are Predictive of Postoperative Foot Drop

Introduction: Intraoperative neuromonitoring (IOM) is commonly used in instrumented spine surgery; however, its utility is often debated. Previous studies indicate that IOM is sensitive and specific for detecting intraoperative injury, but its impact on postoperative outcomes is contested. We examined whether certain preoperative patient characteristics were correlated with IOM alerts and if IOM findings predicted specific postoperative outcomes in minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) surgeries.

Methods: We conducted a retrospective analysis of patients who underwent MIS-TLIF surgery with IOM at a single institution. Collected variables included demographics, comorbidities, history of surgery and trauma, operative spinal levels, IOM findings, and post-operative outcomes. Single- and multi-variate logarithmic regression analyses were performed to assess correlation with IOM alerts. Independent logarithmic and linear regressions were performed to analyze the relationship between IOM alert and postoperative outcomes.

Results: We identified 439 patients who underwent a MIS-TLIF with IOM, 22 of whom experienced an IOM alert. No preoperative variables were significantly associated with IOM alerts. Likewise, stratification by spinal fusion level did not reveal any significant predictors of IOM alert. However, IOM alert significantly increased the log-odds of two postoperative complications: foot drop (95% CI: 1.878-6.496; p< 0.001) and leukocytosis (95% CI: 0.183-5.795; p< 0.05). Additionally, IOM alert was a nearly significant positive predictor for subsidence (95% CI: -0.147-4.733 p=0.065). 2 of the 4 patients experiencing post-operative foot drop reported that the outcome resolved within one-year of the procedure, while the other 2 continued to report foot drop beyond 4 year follow-up.

Conclusion : While our study did not identify any preoperative variables that were significantly associated with IOM alerts, the presence of an IOM alert was strongly predictive of post-operative foot drop. These results suggest a strong benefit for the utilization of IOM in all MIS-TLIF procedures.