Correlative MRI study of acromion morphology and associated rotator cuff tears

Background: Shoulder pain is frequently caused by subacromial impingement or rotator cuff injuries and forms the major indications for presurgical evaluation using MRI. Rotator cuff tears are caused by either internal degenerative changes or extrinsic compression of the acromion on the rotator cuff tendons. Reduction in subacromial space and abnormal acromial morphologies contribute to rotator cuff damage. Hence identifying these acromial abnormalities forms an essential part of evaluation since these forms the main indication for corrective acromioplasty. Methods: This institution-based MRI study was evaluated in three groups as follows: Group1-15 patients with rotator cuff tear; Group 2-15 patients with subacromial impingement; Group 3-10 controls without subacromial impingement pathology and rotator cuff tear and assessed for type of acromion, Lateral Acromial Angle (LAA), Acromion Index (AI), and Acromio-humeral Interval. Results: The type II Acromion showed significant association with rotator cuff tear and subacromial impingement followed by Type III and Type I respectively in our study. However, Type II acromion is relatively commoner in the control study and showed 26.92%, subacromial impingement showed 30.7% and rotator cuff tear showed 42.31%. The distribution of Lateral Acromial Angles differed significantly between the three groups. In comparison to controls, patients with low lateral acromial angle had significant association with subacromial impingement and rotator cuff tears. The age distribution of the Acromial Index differed significantly between the three groups with higher predilection to rotator cuff tear and impingement as age advanced and higher acromial index. Between the three groups, the subjects with low acromio-humeral distance had significant association with rotator cuff tears and impingement. Conclusions: Low lateral acromial angle, larger acromial index, and smaller acromio-humeral interval are related with a higher incidence of subacromial impingement and rotator cuff tears on MRI assessment of the shoulder.