Morphological Characteristics After Single Versus Recurrent Traumatic Posterior Shoulder Dislocation Events.

BACKGROUND: Posterior shoulder dislocations are rare but particularly challenging in high-demand populations. While anterior instability has been well studied, limited data exist on the morphological consequences of traumatic first-time and recurrent posterior dislocations.

PURPOSE: To quantify posterior glenoid bone loss (pGBL), glenoid version, reverse Hill-Sachs lesions, and acromial morphology in patients with traumatic posterior shoulder dislocations and compare these features between the single and recurrent dislocation groups.

METHODS: A retrospective review was conducted using the Military Health System Data Repository to identify patients who sustained traumatic posterior shoulder dislocations between January 2017 and December 2024. These were defined as events requiring manual reduction with subsequent advanced imaging demonstrating a posterior labral tear or posterior bony Bankart lesion, with or without a reverse Hill-Sachs lesion. Morphological features were independently assessed by 2 raters. Measured factors included pGBL (measured by the perfect circle technique (PCT), two-thirds glenoid height methods, and one-third glenoid height method), glenoid version, reverse Hill-Sachs Lesion parameters, and acromial tilt and height. Patients were stratified into single and recurrent dislocation groups. Statistical comparisons were performed using t tests, with significance set at a P value < .05. Linear regression was used to evaluate the relationship between number of dislocations and extent of pGBL.

RESULTS: A total of 39 shoulders sustained posterior dislocation events with adequate imaging. Patients with multiple dislocations (vs a single dislocation) demonstrated significantly greater mean pGBL across all 3 measurement techniques: PCT (12.4% vs 10.5%; P = .031), two-thirds glenoid height method (13.7% vs 11.5%; P = .021), and one-third glenoid height method with sex-specific adjustments (13.0% vs 10.7%; P = .009). Glenoid retroversion was not significantly greater in the recurrent dislocation group (-11.0° vs -8.0°; P = .252). No significant differences were observed in reverse Hill-Sachs lesion dimensions or acromial morphology between groups. A weak positive correlation was found between the number of dislocations and pGBL (R2 = 0.054).

CONCLUSION: After first-time traumatic posterior dislocation, the mean pGBL was approximately 11%. Bone loss increased with recurrent dislocations, approaching thresholds associated with failure after isolated posterior soft tissue stabilization. No association was found with reverse Hill-Sachs lesion size. Early recognition and intervention, particularly in high-demand populations at risk of recurrent dislocation, may be appropriate to prevent pGBL progression.

STUDY DESIGN: Case series; Level of evidence, 4.