Poster 218. Morphological Characteristics Following Single versus Recurrent Traumatic Posterior Shoulder Dislocation Events in a High-Risk Population

Abstract

Objective: Posterior shoulder dislocations are rare but particularly challenging in high-demand populations such as active-duty servicemembers. While anterior instability has been well studied, limited data exist on the morphological consequences of traumatic posterior dislocations. The purpose of this study was to quantify posterior glenoid bone loss (pGBL), glenoid version, reverse Hill-Sachs lesions, and acromial morphology in patients with traumatic posterior shoulder dislocations, and to compare these features between primary and recurrent dislocators. Methods: A retrospective review was conducted using the Military Health System Data Repository (MDR) to identify patients who sustained traumatic posterior shoulder dislocations between January 2017 and December 2024. Inclusion required confirmation via CT or MRI. Morphological features were independently assessed by two orthopedic residents. Measured factors included pGBL (measured by perfect circle, 2/3 glenoid height, and 1/3 glenoid height methods), glenoid version, reverse Hill-Sachs lesion parameters, and acromial tilt and height. Patients were stratified into single and multiple dislocation groups (>=2). Statistical comparisons were performed using t-tests, with significance set at p<0.05. A linear regression evaluated the relationship between number of dislocations and extent of pGBL. Results: Thirty-nine shoulders met inclusion criteria. Patients with multiple dislocations demonstrated significantly greater mean pGBL across all three measurement techniques: perfect circle (12.35% vs. 10.48%, p=0.031), 2/3 glenoid height (13.73% vs. 11.51%, p=0.021), and 1/3 glenoid height with sex-based adjustments (12.99% vs. 10.72%, p=0.009). Although glenoid retroversion was greater in the multiple dislocation group (-11.02° vs. -7.97°), the difference was not statistically significant (p=0.252). No significant differences were observed in reverse Hill-Sachs lesion dimensions or acromial morphology. A weak positive correlation was found between the number of dislocations and pGBL (R²=0.054). Conclusions: Patients with recurrent posterior shoulder dislocations exhibit significantly increased posterior glenoid bone loss compared to those with a single event. These findings underscore the cumulative structural damage associated with repeat posterior dislocations and highlight the importance of early identification and intervention in high-demand populations. Further research is needed to assess the implications of these morphological changes on surgical outcomes and long-term shoulder stability.