Radiographic Assessment and Risk Model of Atlantoaxial Instability Induced by Halo-Pelvic Traction in Treating Severe Spinal Deformity

PURPOSE: Halo-pelvic traction (HPT) is widely used for managing severe rigid scoliosis by enhancing surgical safety. However, complications such as atlantoaxial instability may occur during traction. This study aimed to identify the risk factors for atlantoaxial instability during HPT and assess whether instability is reversible after traction. Additionally, a radiographic criterion based on the lateral mass interval (LMI) was proposed to define this condition. METHODS: A retrospective study was conducted on patients who underwent HPT followed by posterior spinal fusion between March 2014 and August 2022. Atlantoaxial alignment was assessed pre-traction, post-traction, and postoperatively using LMI. Patients were categorized into stable and unstable groups. Risk factors were identified through univariate and multivariable logistic regression analyses, and a nomogram was constructed based on the final predictive model. RESULTS: Among fifty-nine patients, forty-five developed atlantoaxial instability during traction. All cases were radiographically reversible postoperatively. Multivariable analysis identified younger age (OR = 0.893, P = 0.005) and increased pelvic tilt (PT) (OR = 1.137, P = 0.048) as independent risk factors. The predictive model showed good discrimination (AUC = 0.817). CONCLUSION: Atlantoaxial instability during HPT is transient and reversible. LMI is a reliable radiographic indicator for its assessment. Younger age and increased PT are significant predictors, and the proposed nomogram may aid in pre-traction risk stratification.