The effect of spinal cord morphology on intraoperative neuromonitoring alerts in spinal fusion for adolescent idiopathic scoliosis

Background: A spinal cord morphology classification has linked intraoperative neuromonitoring (IONM) alerts in adults undergoing spine deformity correction with spinal cord type. The purpose of this study was to apply the same classification to Adolescent Idiopathic Scoliosis (AIS) patients undergoing spinal fusion and investigate the association of alerts to cord type. Methods: AIS patients with pre-operative MRIs of the neural axis from 2019-2022 who underwent spinal fusion were included. T2-weighted axial MRI images at the deformity’s apex were used to classify spinal cord morphology into 3 types as described by Sielatycki et al. Cord type was associated with preoperative demographic and radiographic findings and the occurrence of IONM alerts during surgery. Results: Eighty-three patients qualified for inclusion. There were 32 (39%) Type 1, 45 (54%) Type 2, and 6 (7%) Type 3 cords. Patients with Type 3 cords demonstrated a significantly larger mean Cobb angle ( P =0.004), coronal DAR ( P =0.002), and larger preoperative kyphosis ( P =0.033). There were 14/83 patients (17%) with IONM alerts: 3/32 (9%) in Type 1, 7/45 (16%) in Type 2, and 4/6 (67%) in Type 3. The odds of an IONM alert were 19.33x greater with a Type 3 cord versus a Type 1 cord ( P =0.003). Males were at greater risk of IOMN alerts ( P =0.042). Conclusions: In a cohort of exclusively AIS patients, a Type 2 cord was the most common (54%). Type 3 cords demonstrated significantly larger coronal and sagittal plane radiographic deformities and demonstrated a 19.33x higher odds ratio of an IONM alert than Type 1. Level of Evidence: Diagnostic Level III