Positional disappearance of motor evoked potentials is much more likely to occur in non-idiopathic scoliosis

PURPOSE: This study evaluates intraoperative disappearance of motor waveforms related to patient positioning in neurologically asymptomatic patients with spinal deformity. METHODS: This is a retrospective review of 190 neurologically asymptomatic patients aged seven to 17 years planned for posterior instrumentation under neuromonitoring. There were 159 patients with adolescent idiopathic scoliosis and 31 patients with secondary scoliosis. Patients underwent surgery with transcranial electric stimulation motor evoked potentials (TES-MEPs). In case of abnormal findings, surgery was temporarily discontinued and necessary measures undertaken. In case of permanent signal disappearance surgery was definitively discontinued. RESULTS: Six patients showed permanent loss of signal during early stages of surgery. These patients had a mean major curve of 64° Cobb angle and a mean thoracic kyphosis (D2 to D12) of 72°. The 184 remaining patients had a mean major curve of 50° Cobb angle and a thoracic kyphosis of 35°. A retrospective descriptive review of the patients’ radiographs shows hyperkyphosis to be the common ground between the six secondary scoliosis cases. Gradual preoperative traction maintained during the surgery applied in two of these patients taken back to surgery six months later was associated with maintenance of TES-MEP signals throughout the surgery. CONCLUSION: This study shows that positional permanent loss of neuromonitoring signals is more likely to occur in patients with secondary scoliosis and hyperkyphosis shown to have sharper spine deformity and suspected to have a more vulnerable spinal cord. Gradual skeletal traction performed in two of these patients and maintained during surgery showed promising results. LEVEL OF EVIDENCE: IV