Technical Feasibility and Preliminary Safety Analysis of Intraoperative Electromyographic Neuromonitoring Using an Insulated Access Needle During Minimally Invasive Lumbar Pedicle Screw Fixation: A Retrospective Multicenter Series

Background Triggered electromyography (t-EMG) is used as an adjunct to fluoroscopy during minimally invasive lumbar pedicle screw fixation to detect potential cortical breaches. Its diagnostic accuracy depends on the electrical isolation properties of the stimulating instrument. Standard non-insulated Jamshidi needles allow current to disperse along the full needle shaft, which may reduce signal specificity at the pedicle tip. An insulated access needle with an adjustable depth stop (ALARA™ Neuro Access Needle; SurGenTec, LLC, Boca Raton, FL, USA) was used with continuous t-EMG monitoring in this series. Screw position was assessed by biplanar fluoroscopy and final t-EMG testing only; no postoperative CT was obtained in asymptomatic patients. Methods Retrospective post-market multi-center series. Three surgeons at independent sites placed 367 percutaneous lumbar pedicle screws in 75 consecutive patients (182 spinal levels, L1-S1, 2020-2021). An ALARA needle threshold of ≥5 mA was the adopted criterion before proceeding to guidewire placement. All patients underwent postoperative neurological assessment. Results No patient sustained a new postoperative neurological deficit attributable to screw malposition. Of 367 screws, 341 (92.9%) were placed without needle repositioning; 26 (7.1%) required repositioning because of sub-threshold EMG readings. One screw (0.3%) produced persistently low EMG values (final screw reading, 9 mA at L4) consistent with possible pedicle cortical proximity; this was flagged clinically, and the patient experienced no neurological sequelae on follow-up examination. ALARA needle readings of ≥5 mA preceded final screw readings of ≥10 mA in all cases in which repositioning was not required, an empirical offset consistent with differences in stimulating surface area between the needle tip and the screw. Conclusions Use of an insulated access needle with continuous t-EMG monitoring identified and enabled real-time correction of suboptimal needle trajectories in 26 of 367 screws (7.1%) before guidewire placement, with zero postoperative neurological deficits across 75 patients at three independent surgical sites using multiple implant systems. A needle-specific threshold of ≥5 mA consistently preceded final screw readings within the published safety range across all treated lumbar and sacral levels. These findings support needle-stage t-EMG monitoring with an insulated access needle as a practical, platform-independent tool for enhancing intraoperative safety during minimally invasive surgical (MIS) lumbar pedicle screw fixation, with prospective CT-correlated studies warranted to establish definitive threshold standards.