The Effect of Traction and Spinal Cord Morphology on Intraoperative Neuromonitoring Alerts in Adolescent Idiopathic Scoliosis

Background: Patients with apical spinal cord deformity have been shown to be at a greater risk for intraoperative neuromonitoring (IONM) alerts when undergoing posterior spinal instrumented fusion (PSF) for adolescent idiopathic scoliosis (AIS). The use of intraoperative traction during deformity correction has also been associated with an increased risk of IONM alerts. With use of the Spinal Cord Shape Classification System (SCSCS), we investigated the interaction between spinal cord type and the use of intraoperative traction and their impact on IONM alerts during the surgical correction of AIS. Methods: A total of 441 consecutive patients who underwent PSF or combined PSF plus anterior spinal fusion (ASF) for AIS between 2003 and 2022 were retrospectively reviewed. Those with major thoracic curves of ≥70° and available preoperative magnetic resonance images (MRIs) were included. Charts were reviewed for IONM alerts and the use of intraoperative traction. Spinal cord morphology was determined using the SCSCS. A multivariable regression model was used to assess the risk factors for an IONM alert. Results: Preoperative MRIs were available for 102 patients. Type-3 cords were present in 15 (14.7%) of the 102 patients. Intraoperative traction was used in 15 (14.7%) of the 102 patients, including 5 with type-3 cords. Patients with type-3 cords were more likely to have an IONM alert than those with type-1 or 2 cords (40.0% [type 3] versus 12.6% [type 1 or 2]; odds ratio [OR], 4.60; 95% confidence interval [CI], 1.34 to 15.53). No such difference was observed between patients with type-1 cords and those with type-2 cords (12.5% and 12.7%, respectively; p > 0.9999). All patients with type-3 cords placed in intraoperative traction experienced IONM alerts, whereas only 10% of patients with type-3 cords not placed in traction experienced such alerts (p = 0.002). Multivariable regression modeling revealed intraoperative traction to be the only independent risk factor for an IONM alert (OR, 9.37; 95% CI, 2.47 to 38.24). Conclusions: This study demonstrated that 14.7% of patients with AIS and curves of ≥70° had a type-3 cord. Intraoperative traction carried a ninefold increased risk of an IONM alert. When intraoperative traction is used for type-3 cords, surgeons should expect IONM alerts to occur. The SCSCS can be condensed into 2 groups for a pediatric population. Level of Evidence: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.