Safety and Feasibility of Transabdominal Muscle Action Potential Monitoring (TMAP) in Lateral Lumbar Surgery

Background Context: Neuromonitoring has improved since its advent in the 20 century, but technological innovations can potentially furthermore specific and advanced analyses to prevent nerve injury.

Purpose: To assess the viability of a novel intraoperative neuromonitoring modality -transabdominal muscle action potential monitoring (TMAP) - to provide reliable monitoring of the cauda equina during lumbar spinal fusion.

Study Design: Multicenter, prospective, single-cohort, technical feasibility study.

Patient Sample: A total of 296 patients who underwent one- or two-level lateral lumbar interbody fusion (LLIF) with TMAP neuromonitoring in the treatment of degenerative lumbar spinal disease were enrolled and analyzed.

Outcome Measures: The feasibility of TMAP to stimulate lower extremity myotomes was measured at baseline and through the procedure.

Methods: LLIF was performed at L4-L5 in all patients and at additional levels when needed. Triggered EMG was utilized, per the surgical technique, to map the trans-psoas surgical corridor. Additionally, TMAP was used to monitor bilateral lower extremity nerve function before, during, and at the end of surgery. Baseline and postoperative myotome activation using TMAP was reported.

Results: In 296 patients included for final analysis, 98.9% of myotomes were activated at baseline and 98.6% of myotomes activated at closure. At least three myotomes were activated in all patients before and after surgery. All 10 myotomes were activated in 94% of patients at baseline and in 93% at closure.

Conclusions: TMAP during lumbar spine surgery is feasible and safe for patients being treated for lumbar degenerative disease, while avoiding some of the drawbacks of transcranial motor evoked potentials (TcMEP). Additional studies are needed to assess clinical correlation between TMAP monitoring and patient outcome.