Construction and Validation of a Nomogram for Predicting the Adding-On Phenomenon Postoperatively for Adolescent Idiopathic Scoliosis: A Retrospective Study.

Objective: To develop and validate a nomogram predicting the postoperative adding-on phenomenon in Lenke 1/2 adolescent idiopathic scoliosis patients, providing a quantitative tool for therapeutic benefit assessment and personalized risk prediction.

Methods: A retrospective analysis was conducted using clinical data from 213 patients. The least absolute shrinkage selection operator was applied to identify the best predictors. Multivariate logistic regression was used to construct a nomogram with a training set (80%), while a validation set (20%) was used for internal validation. The receiver operating characteristic curve, calibration curve, and decision curve analysis assessed the model's clinical utility.

Results: The model was constructed using the 4 best predictor variables: the number of vertebrae in the main thoracic curve, apical vertebra translation, last instrumented vertebra rotation, and Risser sign. The model's C-index was 0.932 (95% confidence interval, 0.8858-0.9775). Decision curve analysis indicated a clinically meaningful high-risk threshold between 0 and 1, and the calibration curve demonstrated satisfactory accuracy.

Conclusions: The model proved useful for predicting the occurrence of adding-on in Lenke 1/2 adolescent idiopathic scoliosis patients after surgery.