Characteristics of Cases with Poor Transcranial Motor-evoked Potentials Baseline Waveform Derivation in Spine Surgery

Abstract

Study Design. Prospective multicenter study. Objective. The purpose of the study is to examine cases with poor baseline waveform derivation for all muscles in multichannel monitoring of transcranial motor-evoked potentials (Tc-MEPs) in spine surgery. Summary of Background Data. Intraoperative neuromonitoring (IONM) is useful for identifying neurologic deterioration during spinal surgery. Tc-MEPs are widely used for IONM, but some cases have poor waveform derivation, even in multichannel Tc-MEP monitoring. Methods. The subjects were 3625 patients (mean age 60.1 years, range 4–95; 1886 females, 1739 males) who underwent Tc-MEP monitoring during spinal surgery at 16 spine centers between April 2017 and March 2020. Baseline Tc-MEPs were recorded from the deltoid, abductor pollicis brevis, adductor longus, quadriceps femoris, hamstrings, tibialis anterior, gastrocnemius, and abductor hallucis (AH) muscles after surgical exposure of the spine. Results. The 3625 cases included cervical, thoracic, and lumbar lesions (50%, 33% and 17%, respectively) and had preoperative motor status of no motor deficit, and motor deficit with manual muscle testing (MMT) ≥3 and MMT <3 (70%, 24% and 6%, respectively). High-risk surgery was performed in 1540 cases (43%). There were 73 cases with poor baseline waveform derivation (2%), and this was significantly associated with higher body weight, body mass index, thoracic lesions, motor deficit of MMT <3, high-risk surgery (42/1540 [2.7%] vs. 31/2085 [1.5%], P < 0.05), and surgery for ossification of the posterior longitudinal ligament (OPLL). Intraoperative waveform derivation occurred in 25 poor derivation cases (34%) and the AH had the highest rate. Conclusion. The rate of poor baseline waveform derivation in spine surgery was 2% in our series. This was significantly more likely in high-risk surgery for thoracic lesions and OPLL, and in cases with preoperative severe motor deficit. In such cases, it may be preferable to use multiple modalities for IONM to derive multichannel waveforms from distal limb muscles, including the AH. Level of Evidence: 3

The Utility of Transcranial Stimulated Motor-Evoked Potential Alerts in Cervical Spine Surgery Varies Based on Preoperative Motor Status

“…13,14 The AH should be included as a test muscle because the highest waveform derivation rate from the AH has been reported even in cases of severe motor deficits. 11,14,15 Furthermore, preoperative spinal cord fragility may increase the risk of postoperative nerve damage due to surgical manipulation, which may be the high-risk cases in intramedullary spinal cord tumor resection and thoracic OPLL surgeries, with poorer outcomes being achieved for patients with a severe motor status. 2,3 The utility of the 70% threshold was reported in the high-risk group, as in the previous reports, [8][9][10] and especially in intradural spinal tumors surgery, where PPV was higher than the other surgeries (Supplemental Fig.…”

“…In these cases, Tc-MEP from distal muscles, such as AH, which is richly innervated by lateral corticospinal tract fibers, may be particularly effective 13,14. The AH should be included as a test muscle because the highest waveform derivation rate from the AH has been reported even in cases of severe motor deficits 11,14,15. Furthermore, preoperative spinal cord fragility may increase the risk of postoperative nerve damage due to surgical manipulation, which may be the high-risk cases in intramedullary spinal cord tumor resection and thoracic OPLL surgeries, with poorer outcomes being achieved for patients with a severe motor status 2,3…”

“…Although the deterioration of Tc-MEP has been identified as a useful predictor of postoperative paralysis,2,3,20 the Tc-MEP waveform alone may be limited in its ability to confirm the accuracy of the alert. In addition, the preoperative severe motor deficit is associated with the poor derivation of the Tc-MEP waveform 11,14,15. A combination of Tc-MEP and the D-wave was recently shown to be the most suitable for predicting motor paralysis 9,21.…”

“…In addition, the preoperative severe motor deficit is associated with the poor derivation of the Tc-MEP waveform. 11,14,15 A combination of Tc-MEP and the D-wave was recently shown to be the most suitable for predicting motor paralysis. 9,21 Therefore, preparation for the D-wave may increase the safety of surgery on cases at an increased risk of paralysis during surgery in addition to multichannel Tc-MEP including distal muscles.…”

Characteristics of Tc-MEP Waveforms in Spine Surgery for Patients with Severe Obesity

“…40,41 In our series, both a preoperative motor deficit with MMT <3 and BMI >35 kg/m 2 were found to be independent risk factors for undetectable baseline waveforms in all muscles in multivariate analysis. Previously, we have reported that severe motor deficit is a risk factor for significantly poor waveform derivation at baseline, 42 but a detailed study with a focus on severe cases has not been performed. Since the number of cases with preoperative motor deficit was significantly higher in severely obese cases, these two factors appear to be significantly related, and therefore the hazard ratio calculated in the present study can be viewed as a new finding.…”