Comparison of Glenoid Bone Loss After Unidirectional Versus Combined Shoulder Instability in a Military Population.

Background: While glenoid bone loss (GBL) after anterior shoulder instability correlates with poor functional outcomes, the specific effects of GBL in posterior and combined-type shoulder instability remain poorly characterized, especially in a high-risk military population. Purpose/Hypothesis: The purpose of this study was to compare GBL between unidirectional anterior or posterior instability versus combined-type instability in active-duty servicemembers. It was hypothesized that total GBL and GBL in the direction of instability would be greater in those with combined-type instability compared with unidirectional instability. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Active-duty servicemembers who underwent shoulder stabilization surgery between January 2010 and December 2019 were eligible for inclusion. Patients with multidirectional instability, concomitant rotator cuff tears, osteochondritis dissecans of the glenoid or humeral head, superior labral anterior-posterior tears, biceps pathologies, and humeral avulsion of the glenohumeral ligament were excluded. Patients were grouped according to direction of instability (anterior, posterior, or combined), and patient characteristics, instability characteristics, suture anchor use, and GBL were compared between the 3 cohorts. Results: In total, 117 patients met the study inclusion criteria. The mean patient age was 29 years, 89.7% were male, the dominant extremity was involved in 63.2%, 65.8% attributed their injuries to a singular traumatic event, and the mean follow-up was 7.9 years. There was no significant difference regarding patient characteristics, injury mechanism, or follow-up time between the 3 cohorts. As compared with the combined-type instability cohort, mean anterior GBL was greater in the anterior instability cohort (8.00% ± 4.40% vs 4.98% ± 5.26% for combined; Conclusion: GBL in the direction of instability was found to be significantly greater in the unidirectional versus combined-type instability cohorts.