Objective: Os acromiale is a variation that develops due to the fusion defect in the ossification process of the scapula. Thus, the acromion becomes an accessory bone separate from the spine of the scapula. Various opinions have been reported about the presence and frequency of os acromiale in the studies conducted. The aim of this study is to determine the prevalence of os acromiale in Tokat, gender distribution and the anatomical region where fusion defect is most common, using magnetic resonance imaging (MRI) method.

Material and Method: A total of 864 shoulder MRI images of individuals aged 30-90 who applied to the Health Research and Application Center of Tokat Gaziosmanpasa University, who had no history of trauma, operation, fracture and who had shoulder MRI for any reason were evaluated.

Results: Os acromiale was detected in 54 of the shoulder MRIs evaluated in our study. Os acromiale was found in 8 (2,02%) shoulders in men and 46 (9,80%) in women. It was determined that it was more common in women (p ≤0,05). When os acromiale types were evaluated in the cases and when compared in terms of gender, 42 meso-acromions (36 females, 6 males) were observed, 10 preacromions (all in females) and 2 metaacromions (all in males) were detected.

Conclusion: The prevalence of os acromiale was measured as 6,25%. It was significantly more common in women than men, and meso-acromion type os acromiale was found more frequently (77,77%) than the other types.