Development and internal validation of a preliminary nomogram for the early prediction of chronic ankle instability following a first-episode lateral ankle sprain with acute-phase MRI indication

Introduction – Chronic ankle instability (CAI) is a common sequela following acute lateral ankle sprain (LAS). In order to treat acute lateral ankle sprains more effectively, it is important to recognize patients who are at high risk of developing CAI. The aim of this study is to develop a Nomogram to predict the risk of developing CAI after the onset of the first LAS. Method – This study included 181 patients diagnosed with their first LAS between December 1, 2017, and December 1, 2020, who received plain radiograph and MRI scanning within the first 2 weeks after LAS. Independent risk factors for CAI post-initial LAS were determined through separate univariate and multivariate analyses. The clinical utility and predictive efficacy of the nomogram were evaluated using the C-index, area under the receiver operating characteristic (ROC) curve, calibration curves, and decision curve analysis. Internal validation was assessed by bootstrap validation. Results – Multivariate analysis identified five significant predictors for CAI: age ≤ 23 years, body mass index (BMI) of 24–28 kg/m² and BMI ≥28 kg/m², injury to the posterior talofibular ligament, a large bone marrow lesion of the talus, and Grade 2 tibial talar joint effusion. The prediction model demonstrated good discrimination, with an apparent C-index of 0.831 and an AUC of 0.818. Bias-corrected internal validation yielded a C-index of 0.816. The calibration curve showed strong agreement between predicted probabilities and actual outcomes. Conclusion – Pending external validation in diverse prospective cohorts, this internally validated preliminary nomogram demonstrates potential to predict the risk of CAI development after a first episode of LAS in patients who underwent acute-phase MRI scanning. This tool may help identify high-risk patients but requires rigorous external validation before clinical implementation.