Acromial shapes and extension of rotator cuff tears: magnetic resonance imaging evaluation.

Magnetic resonance imaging makes it possible to inspect the status of the rotator cuff and the shape of the acromion. To clarify the relationship between acromial shapes and rotator cuff tears, we evaluated magnetic resonance images obtained in 192 shoulders. We classified the acromial shapes into 3 types: type I (flat), type II (curved), and type III (hooked). Among a group of 91 shoulders with rotator cuff tears, 33 (36.3%) were type I, 22 (24.2%) type II, and 36 (39.6%) type III. The size of rotator cuff tears in type III acromions was significantly larger than in type I or II acromions. Comparison of the incidence of each acromial shape between groups of specimens with and without rotator cuff tears revealed no significant differences. We suggest that whereas acromial shapes have a bearing on the extent of rotator cuff tears, the correlation between rotator cuff tears and a type III acromion is not as strong as has been suggested in the literature.