A Novel Method for Estimating Three-Dimensional Apical Vertebral Rotation Using Two-Dimensional Coronal Cobb Angle and Thoracic Kyphosis

Abstract Study Design Retrospective cohort analysis. Objectives To use a large cohort of three-dimensional (3D) spinal reconstructions to create a simple mathematical formula capable of estimating 3D apical vertebral rotation (AVR) based on the correlation with routinely obtained two-dimensional (2D) measurements of scoliosis. Summary of Background Data Quantification of vertebral rotation in AIS using 2-dimensional (2D) imaging is inherently challenging as the axial plane cannot be directly visualized. Methods A database of 279 3D spinal reconstructions was queried for patients with thoracic major adolescent idiopathic scoliosis (AIS). 2D thoracic Cobb angle, T5–T12 thoracic kyphosis, pelvic incidence, sacral slope, and pelvic tilt were recorded. 3D AVR was calculated for each patient from 3D reconstructions. Patients were divided into development (n = 186) and validation (n = 93) cohorts. Within the development cohort, univariate analysis was performed between 2D measurements and 3D AVR with significance set at p Results Only 2D thoracic Cobb and T5–T12 thoracic kyphosis had significance in univariate (p R = 0.739, r 2 = 0.54). In testing with the validation cohort, the model proved generalizability ( R = 0.703) and had a mean absolute error Conclusions This model is capable of estimating 3D AVR given 2D thoracic Cobb and T5–T12 kyphosis. The accuracy of this method is comparable to previously reported methods of 2D axial rotation measurement. However, this model provides 3D axial rotation and requires no physical instruments, non-standard measurements, or software programs. Such a model is valuable for both routine evaluation of AIS and operative preparation. Level of Evidence Level II, diagnostic.