These authors point out that there are differences in scapular shape between shoulders with rotator cuff tears (RCT) and osteoarthritic shoulders (OA). They analyzed the orientation and shape of the acromion in 70 shoulders with massive degenerative RCT (apparently those having subsequent reverse total shoulders) and 45 shoulders with concentric OA (apparently those having subsequent anatomic total shoulders) using multiplanar computed tomography (CT) analysis.
They found that lateral acromial roof extension was an average of 4.6 mm wider and the acromial area was an average of 156 mm2 larger in RCT than in COA (P < .001). Significant differences of the lateral extension of the acromion margin were limited to the anterior two-thirds. Acromial roof orientation in RCT was average of 10.8° more “externally rotated” (axial plane: P < .001) and an average of 7.8° more tilted downward (coronal plane: P < .001) than in COA. The glenoid in RCT was an average of 5.5° (P < .001) more covered posteriorly compared with COA.
Comment: It is understood that loading of the acromion is different in patients with massive cuff tears than in patients with concentric osteoarthritis and that these changes are reflected by radiographic changes in acromial shape. Compare the acromial shape in the upper AP x-ray of a shoulder with a massive cuff tear with that in the lower AP x-ray of a shoulder with concentric osteoarthritis.
It seems likely that the acromial changes are likely to be adaptive in response to the change in loading of the acromion in patients with massive cuff tears. In 1972 Neer observed "a characteristic ridge of proliferative spurs and excrescences on the undersurface of the anterior process (of the acromion), apparently caused by repeated impingement of the rotator cuff and the humeral head, with traction of the coracoacromial ligament. . . . Without exception it was the anterior lip and undersurface of the anterior third that was involved."(see this link)
Evidence remains lacking that surgical alteration of the acromial shape can change the natural history of cuff disease (see this link) or of osteoarthritis.
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