Incidence of Shoulder Instability Pathology for Incoming US Service Academy Members: A Magnetic Resonance Imaging Cohort Study- MHSRS 2026

j dowe, m bradley, h gibbs, j robins, r waltz, l Leclere, k cameron, m donahue, m slabaugh, t dekker, j dickens

Abstract accepted for podium presentation at the 2026 Military Health System Research Symposium (MHSRS)

INTRODUCTION: US service academy members have a 20x higher risk of sustaining a shoulder instability event during their time of enrollment compared to the general population. As a result, great efforts have been made to identify risk factors, optimize treatment, and promote return to duty strategies. The purpose of this study was to understand rates of morphological variations in shoulders and how this relates to injury risk.

MATERIALS AND METHODS: This IRB-approved study voluntarily recruited freshman at the beginning of their enrollment at three major service academies (USAFA, USMA, and USNA). Participants consented to provide bilateral shoulder magnetic resonance imaging (MRI) studies, injury history details, and baseline functional assessments. Shoulder instability events after enrollment were identified for further analysis. All MRIs of those with pre-existing shoulder injuries were measured and evaluated for comparison to the MRI of the uninjured shoulder. A paired t-test was performed to compare morphological measurements within subjects.

RESULTS: 10 individuals were removed due to having a history of bilateral instability. 66 individuals with a prior instability event in a single shoulder completed screening MRIs post-enrollment. A total of 132 shoulder MRIs were measured and analyzed. Mean glenoid bone loss (GBL) was significantly greater in injured shoulders compared to healthy shoulders (9.1% vs 6.2%, p<0.001). Injured shoulders also demonstrated significantly greater glenoid retroversion (8.2° vs 1.5°, p<0.001), and reduced posterior acromial tilt (36.2° vs 53.1°, p<0.001) relative to healthy shoulders. Hill-Sachs lesions (HSL) were present in 65 of 66 injured shoulders, with a mean lesion area of 0.7mm2. As of June 2025, 10 of these 66 shoulders with a pre-existing injury went on to have subsequent injury and shoulder stabilization surgery.

CONCLUSIONS: Shoulder instability events are especially common in individuals during their military career. We identified 66 service academy freshmen presenting with pre-existing shoulder instability pathology on MRI, and 15.2% went on to have subsequent shoulder instability events and surgery. In the injured shoulders, we identified a moderate rate of GBL and glenoid retroversion, and a 98% rate of HSL on screening MRIs. These findings highlight the incidence of shoulder instability injuries early in military careers, emphasizing the importance of efficient management to allow for enhanced long-term readiness.