Evaluation of the Instability Severity Index score in predicting failure following arthroscopic Bankart surgery in an active military population

Background: The Instability Severity Index (ISI) score is a preoperative risk stratification tool used to identify patients at heightened risk of recurrent anterior instability after an arthroscopic Bankart procedure. The primary objective of this study was to validate the utility of the ISI score in predicting failure of primary arthroscopic Bankart surgery in an active-duty military population. Methods: A retrospective study was performed to compare all military service members undergoing primary arthroscopic Bankart repairs at a single military treatment facility between 2007 and 2014. The primary outcome of interest was surgical failure due to recurrent instability. The ISI framework was used to stratify each patient for recurrence, and multivariate analysis was performed to evaluate the composite ISI score and individual domains between patients with and patients without failed Bankart repairs. Results: A total of 131 patients were identified, with a mean patient age of 26.8 years (range, 19-47 years), among whom 42 patients (32%) were identified as having a higher-demand military occupation. At a minimum 2-year follow-up, 34 patients (26%) sustained recurrent anterior shoulder instability. The mean ISI score of patients in the failed Bankart repair group was not statistically different than that of patients with a successful repair (3.41 vs 3.5, P =.74), and no individual ISI domains were identified as independent risk factors for subsequent surgical failure or revision stabilization. Conclusion: Contrary to the findings of previous validation studies, the composite ISI score and its individual risk factors were not predictive of subsequent surgical failure after primary arthroscopic Bankart repair in an active military population.