Is there an association between the individual anatomy of the scapula and the development of rotator cuff tears or osteoarthritis of the glenohumeral joint?

TLDR

The authors hypothesised that a large acromial cover with an upwardly tilted glenoid fossa would be linked to degenerative rotator cuff tears, while a short acromion with an inferiorly inclined glenoid would be linked to glenohumeral osteoarthritis. They tested this by measuring a new radiological metric, the critical shoulder angle (CSA), which integrates glenoid inclination and acromion lateral extension, on radiographs of 94 asymptomatic controls, 102 shoulders with full‑thickness rotator cuff tears, and 102 shoulders with primary osteoarthritis. The CSA was significantly larger in the rotator cuff tear group (mean 38.0°) and smaller in the osteoarthritis group (mean 28.1°), with 84 % of patients having CSA > 35° in the tear group and 93 % having CSA < 30° in the OA group, indicating that distinct shoulder anatomies are associated with specific degenerative joint disorders.

Abstract

We hypothesised that a large acromial cover with an upwardly tilted glenoid fossa would be associated with degenerative rotator cuff tears (RCTs), and conversely, that a short acromion with an inferiorly inclined glenoid would be associated with glenohumeral osteoarthritis (OA). This hypothesis was tested using a new radiological parameter, the critical shoulder angle (CSA), which combines the measurements of inclination of the glenoid and the lateral extension of the acromion (the acromion index). The CSA was measured on standardised radiographs of three groups: 1) a control group of 94 asymptomatic shoulders with normal rotator cuffs and no OA; 2) a group of 102 shoulders with MRI-documented full-thickness RCTs without OA; and 3) a group of 102 shoulders with primary OA and no RCTs noted during total shoulder replacement. The mean CSA was 33.1° (26.8° to 38.6°) in the control group, 38.0° (29.5° to 43.5°) in the RCT group and 28.1° (18.6° to 35.8°) in the OA group. Of patients with a CSA > 35°, 84% were in the RCT group and of those with a CSA < 30°, 93% were in the OA group. We therefore concluded that primary glenohumeral OA is associated with significantly smaller degenerative RCTs with significantly larger CSAs than asymptomatic shoulders without these pathologies. These findings suggest that individual quantitative anatomy may imply biomechanics that are likely to induce specific types of degenerative joint disorders.