Transabdominal Motor Action Potentials (Tamap) for Lateral Approach Neuromonitoring in Spine Surgery: Novel Case Series of 51 Patients in Proof-ofConcept Demonstration

Background: Risk of nerve injury is well-documented in lateral approach spine surgery. Advanced intraoperative neuromonitoring techniques may improve false positive and false negative rates of traditional methods to decrease complications. Objective: Determine the safety, sensitivity, and methodological validity of transabdominal motor action potentials (TaMAP) recordings in lateral access spine surgery. Methods: Institutional Review Board approval was obtained for the prospective collection of patient data. Cathode and anode leads were placed on the posterior and anterior surfaces of back and abdomen, and motor responses were recorded by subdermal needle electrodes in 6 target muscles. Voltage and stimulation amplitude were measured at preoperative baseline, postoperative, and new baseline time points, and compared for muscle groups relevant to symptoms and operative approach. Results: In a total of 51 cases of lateral approach surgery, stimulation sensitivity was 100% for vastus medialis, anterior tibialis, and adductor magnus, followed by 98% in biceps femoris, 95% in gastrocnemius, and 33% for vastus lateralis measures. Decompression at L5/S1 resulted in a decrease in voltage in right gastrocnemius in 80% of cases, 80% of right vastus medialis (L3/L4), and in 58% of right anterior tibialis recordings (L4/5). No postoperative neurological complications were observed. Conclusions: TaMAP intraoperative monitoring is a safe, reliable, and sensitive MEP measure with ease-of-use that may serve as an alternative resource in neuromonitoring for spinal surgery. Sensitivity was observed to be as high as 100% for 3/6 muscle groups tested and with robust efficacy of decompression across a variety of procedures and pathologies, including degenerative spine disease and spinal tumor.