Vijay Kumar K. R.1 , Kamesh G.2 , Ranjitha Kulkarni3
BACKGROUND Subacromial impingement and rotator cuff tears are common causes of shoulder pain and indications for MRI shoulder. They often require surgical treatment. The underlying causes for the same are still poorly understood. Both intrinsic degenerative changes in the rotator cuff tendons and extrinsic compression by the acromion are responsible for rotator cuff tears. Certain acromial morphologies contribute to rotator cuff injury by decreasing the subacromial space. Identification of these acromial morphology becomes important as indications for acromioplasty are based on both clinical symptoms and changes in acromial morphology on MRI. METHODS Type of acromion, Lateral Acromial Angle (LAA), Acromion Index (AI) and Acromiohumeral Interval were measured on MRI from 15 patients with supraspinatus tears, 15 patients with subacromial impingement, and 10 controls without subacromial pathology. RESULTS There was no significant difference in the type of Acromion between the three groups. None of the controls had type III acromion, in contrast to 20% of subacromial impingement and rotator cuff tear patients. There was significant difference in Lateral Acromial Angle distribution between three groups. Low acromion angles were found in patients with rotator cuff tear in comparison to controls and patients with subacromial impingement. An angle of <70 degrees, occurred only in patients with rotator cuff tears (n=2). There was significant difference in Acromial Index distribution between the three groups. However, the difference between rotator cuff tear and impingement patients did not reach statistical significance. There was significant difference in Acromiohumeral Interval distribution between the three groups. Significantly low values were found in patients with rotator cuff tear. Mean age of controls (46.00 ± 7.50 years) and patients with subacromial impingement (50.14 ± 7.62 years) were similar, but those of controls and rotator cuff tear patients (60.07 ± 6.25 years) and impingement and rotator cuff patients were different. CONCLUSIONS Morphologic parameters of acromion such as low lateral acromial angle, higher acromial index and lesser acromiohumeral interval are associated with higher prevalence of subacromial impingement and rotator cuff tears and can be measured using MRI. An extremely hooked anterior acromion with lateral acromial angle of less than 70° occurred only in patients with rotator cuff tears.
