The primary aim of this research was to define the range of application and limitations of transcranial motor-evoked potentials (Tc-MEPs) for nerve root monitoring during adult spinal deformity (ASD) operations. Concerns exist about Tc-MEPs’ ability to identify nerve root injuries (NRIs) during ASD operations. 

This study is the first prospective analysis of neuromonitoring data collected by 14 institutions between 2017 and 2020. Patients with ASD who had posterior corrective fusion surgery with multichannel Tc-MEPs served as subjects for this study. Postoperative nerve root symptoms in the targeted muscles were regarded as indicative of NRI if the focal Tc-MEP alarms were met within a few days of surgical treatments. 

There were a total of 311 patients with ASD were analyzed (262 females and 49 males, with a mean age of 65.5 years). There were 47 cases of warnings detected by Tc-MEP, or 15.1% of all cases; 25 alerts occurred after 10 deformity repairs, 6 3-column osteotomies, 4 interbody fusions, 3 pedicle screw placements, or 2 decompressions; and 22 alerts occurred regardless of surgical techniques. About 14 patients (4.5%) experienced postoperative neurological impairment diagnosed as NRI; 11 of these were accurate diagnoses, while 3 were false negatives (FN). There was 1 FN that was not measured at target muscles, and the losses of 2 others were less than 70% of baseline (46% and 65%, respectively). Preexisting motor weakness (P<0.001, odds ratio=10.41) and 3-column osteotomies (P=0.008, odds ratio=7.397) were found to be risk factors of NRI in a multivariate logistic regression study. 

Using multichannel Tc-MEPs with a 70% fall in amplitude as an alarm threshold, researchers could predict nerve root injury in their ASD population. They recommend that future studies examine the impact of a more comprehensive evoked muscle selection and an idealized warning threshold (e.g., 50%) on minimizing false negatives.