Clinical predictive model of lumbar curve Cobb angle below selective fusion for thoracic adolescent idiopathic scoliosis: a longitudinal multicenter descriptive study

Purpose To implement a clinically applicable, predictive model for the lumbar Cobb angle below a selective thoracic fusion in adolescent idiopathic scoliosis. Methods A series of 146 adolescents with Lenke 1 or 2 idiopathic scoliosis, surgically treated with posterior selective fusion, and minimum follow-up of 5 years (average 7) was analyzed. The cohort was divided in 2 groups: if lumbar Cobb angle at last follow-up was, respectively, >= or < 10 degrees. A logistic regression-based prediction model (PredictMed) was implemented to identify variables associated with the group >= 10 degrees. The guidelines of the TRIPOD statement were followed. Results Mean Cobb angle of thoracic main curve was 56 degrees preoperatively and 25 degrees at last follow-up. Mean lumbar Cobb angle was 33 degrees (20; 59) preoperatively and 11 degrees (0; 35) at last follow-up. 53 patients were in group >= 10 degrees. The 2 groups had similar demographics, flexibility of both main and lumbar curves, and magnitude of the preoperative main curve, p > 0.1. From univariate analysis, mean magnitude of preoperative lumbar curves (35 degrees vs. 30 degrees), mean correction of main curve (65% vs. 58%), mean ratio of main curve/distal curve (1.9 vs. 1.6) and distribution of lumbar modifiers were statistically different between groups (p < 0.05). PredictMed identified the following variables significantly associated with the group >= 10 degrees: main curve % correction at last follow-up (p = 0.01) and distal curve angle (p = 0.04) with a prediction accuracy of 71%. Conclusion The main modifiable factor influencing uninstrumented lumbar curve was the correction of main curve. The clinical model PredictMed showed an accuracy of 71% in prediction of lumbar Cobb angle >= 10 degrees at last follow-up.