Objective To analyze the relationship between the morphological characteristics and rotator cuff tear (RCT) by MR.Methods The data of clinic and shoulder MRI of 37 patients with RCT (patients group) were analyzed retrospectively,and 19 healthy volunteers were collected in control group.The acromial shapes were classified into type Ⅰ (flat),type Ⅱ (curved),type Ⅲ (hooked) and type Ⅳ (convex).Additional measurements about pathogenesis of RCT including acromio-humeral distance (AHD),acromial index (AI),lateral acromial angle (LAA) and acromial thickness were performed for further assessment.Results Type Ⅱ was the most commonly encountered acromial shape in patients group (16/37,43.24 ％) and control group (11/19,57.89 ％).There was no statistically significant difference in the incidence of each acromial shape between two groups (P＞0.05).However,the AHD,AI,LAA and acromial thickness showed statistically significant difference between the patients group and control group (all P＜0.05).The type Ⅲ acromion was signifi candy different from the other types in patients group (P＜0.05).Conclusion MRI can clearly display RCT.The AHD and LAA are smaller,the AI and acromial thickness are bigger in RCT patients.Type Ⅲ acromion may increase risks for RCT.