Intraoperative Neuromonitoring Changes During MIS-TLIF Associated with Postoperative Foot Drop

Background/Objectives: Intraoperative neuromonitoring (IOM) is commonly used in instrumented spine surgery; however, its utility is often debated. We sought to determine if IOM changes were independently associated with specific postoperative outcomes in minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF). Methods: We performed a retrospective analysis of patients who underwent MIS-TLIF with IOM at a single institution. Collected data included demographics, comorbidities, surgical history, operative indications, operative spinal levels, IOM findings, and postoperative outcomes. Single and multivariate logarithmic regression analyses were performed to assess the correlation of each preoperative variable with IOM alerts, as well as the association between IOM alerts and postoperative outcomes. Results: A total of 439 patients were identified, 21 of whom experienced an IOM alert. No preoperative variables were significantly associated with IOM alerts. However, the presence of an IOM alert significantly increased the log odds of postoperative foot drop (1.93-6.55, p < 0.001), for which there was also a high specificity (95.9%) and negative predictive value (99.8%). However, likely due to low event rates, IOM had a low negative predictive value (16.7%). Further multivariate analysis also identified an IOM alert as a significant predictor of postoperative neurological deficits and chronic complications, although these pooled categories included foot drop. When IOM subtypes were investigated, both the SSEP and MEP significantly increased the log odds of postoperative foot drop (p < 0.001). Conclusions: An IOM alert during MIS-TLIF may be associated with chronic complications and postoperative neurological deficits, particularly foot drop. These findings highlight IOM's potential use as an effective intraoperative screening tool to rule out iatrogenic foot drop but also its limited value to independently predict rare postoperative complications.