Prevalence of os acromiale and concomitant rotator cuff tears: a focused assessment of 3697 shoulder magnetic resonance imagings

Abstract

The purpose of this study was to define the prevalence of os acromiale on magnetic resonance imaging (MRI) in patients presenting with shoulder pain, to document how often it coexists with rotator cuff tears, and to assess whether focused review detects this variant more reliably than routine radiology reporting. Methods: A retrospective review was conducted on 3697 shoulder MRI examinations obtained between 2020 and 2025 at a tertiary referral center. All studies were independently evaluated by 2 fellowship-trained shoulder surgeons and 1 musculoskeletal radiologist, focusing specifically on the presence, subtype, and coexistence of os acromiale with rotator cuff pathology. Interobserver reliability was assessed using Cohen’s kappa coefficient, and findings were compared with the original radiology reports. Results: Os acromiale was identified in 26 cases, corresponding to a prevalence of 0.7%. Only 11 cases were mentioned in the original radiology reports. Interobserver agreement between shoulder surgeons was almost perfect (κ = 0.98) and excellent between surgeons and the radiologist (κ = 0.92). Subtypes included 12 preacromion, 13 mesoacromion, and 1 metaacromion. Rotator cuff tears were present in 20 of 26 patients with os acromiale (77%), including isolated supraspinatus tears (n = 9), combined supraspinatus–infraspinatus tears (n = 4), supraspinatus–subscapularis tears (n = 3), massive tears (n = 2), and cuff tear arthropathy (n = 2). Conclusion: Os acromiale was uncommon in this MRI-based cohort but frequently coexisted with full-thickness rotator cuff tears. Although causality cannot be inferred, this coexistence may carry clinical relevance. Notably, focused evaluation documented more cases than routine radiology reports, underscoring the added value of targeted assessment. Level of Evidence: Level IV, Diagnostic study. © 2026, AVES. All rights reserved.