Are scapular morphologic characteristics or rotator cuff tear patterns associated with acetabularization of the coracoacromial arch?

PURPOSE: To determine whether rotator cuff tear (RCT) patterns and scapular morphologic characteristics are associated with acetabularization of the coracoacromial arch when the remaining rotator cuff cannot stabilize the humeral head centered on the glenoid. METHODS: Thirty-two consecutive patients incapable of stabilizing the humeral head within the native glenoid were included and divided into 2 groups: unstable glenohumeral fulcrum kinematics (GHFK) group (n = 16; absence of acetabularization of the coracoacromial arch) and captured GHFK group (n = 16; the presence of acetabularization of the coracoacromial arch). Magnetic resonance imaging (MRI) analysis included tear locations, tear extensions (anterior, posterior, and global), and fatty infiltration of the rotator cuff muscles. Plain radiographic and computed tomography image measurements included acromiohumeral distance, critical shoulder angle, lateral acromial angle, acromial index, acromial tilt, acromial slope angle, anterior and posterior acromial coverage, and coracoacromial ligament coverage. RESULTS: Patient demographic characteristics did not differ significantly (P > .05). No differences in tear patterns were found between patients with unstable GHFK and those with captured GHFK on MRI (P > .05). Scapular morphologic parameter measurements showed significant differences between the unstable and captured GHFK groups: anterior acromial coverage (–5.8 ± 13.8° vs. 13.8 ± 11.3°, P < .001), acromial tilt (34.9 ± 8.9° vs. 26.7 ± 6.2°; P = .005), and acromial slope angle (24.5 ± 8.1° vs. 33.5 ± 7.9°, P = .003). CONCLUSION: Scapular morphologic characteristics, rather than RCT patterns, were associated with the development of acetabularization of the coracoacromial arch when the remaining rotator cuff could not stabilize the humeral head. Patients with captured GHFK exhibited larger anterior acromial coverage, smaller acromial tilt, and a more curved acromion than those with unstable GHFK.