Postoperative adding-on phenomenon in Lenke 1A/B and 2A/B adolescent idiopathic scoliosis: risk factors and predictive index.

Purpose: The aim of this study was to identify associated risk factors of distal adding-on phenomenon in Lenke 1A/B and 2A/B adolescent idiopathic scoliosis (AIS) patients and establish the corresponding prediction model.

Methods: The clinical data of 119 Lenke 1A/B and 2A/B AIS patients were retrospectively analyzed. Preoperative, first erect (FE) radiographic parameters and radiographic parameters at the last follow-up were measured. Patients were divided into the adding-on group and the no adding-on group according to whether the adding-on phenomenon was observed at the last follow-up. Univariate analysis and multivariate logistic regression analysis were used to establish the corresponding prediction model.

Results: Adding-on affected 39 (32.8%) patients at the last follow-up. Risser sign and 19 radiographic parameters showed significant differences between the two groups by univariate analysis. Stepwise logistic regression analysis found that the Risser sign and so on five predictor variable, and the nomogram was drawn. The calibration curve showed that the model fitted well. The area under the receiver operating characteristic (ROC) curve is 0.949. And the decision curve analysis curve model within the threshold range for interventions to improve clinical outcomes. There was no significant difference in SRS-22 scores between the two groups.

Conclusions: This study established a prediction model with adding-on in Lenke 1A/B and 2A/B AIS patients. The nomogram contains five predictive variables, which can effectively predict the probability of adding-on phenomenon during follow-up, and may have greater clinical value for the treatment and prevention of adding-on phenomenon.