Glenoid Retroversion Associates With Asymmetric Rotator Cuff Muscle Atrophy in Those With Walch B-type Glenohumeral Osteoarthritis.

BACKGROUND Our purpose was to determine whether glenoid retroversion associates with asymmetric rotator cuff muscle atrophy in eccentric glenohumeral osteoarthritis (GHOA) and if this asymmetry is worsening of GHOA-related atrophy. METHODS Two groups of shoulder magnetic resonance images were studied: patients older than 50 years without a rotator cuff tear or GHOA (control group) and patients preoperative to anatomic total shoulder arthroplasty (GHOA group). Retroversion and rotator cuff muscle cross-sectional areas were measured using reliable and accurate techniques. Proportional muscle areas were created by dividing by total cuff area to correct for differences in overall patient size. Walch grades were assigned via consensus. RESULTS The control group consisted of 102 patients and the GHOA cohort consisted of 141 patients. Within the eccentric GHOA group, retroversion associated with relative increasing supraspinatus (r = 0.268, P = 0.035), increasing infraspinatus (r = 0.273, P = 0.032), and decreasing subscapularis areas (r = -0.343, P = 0.006). However, the combined GHOA group had a significantly higher relative subscapularis area than the control group (P = 0.026). CONCLUSION In the eccentric GHOA, increasing retroversion is associated with increasing volume of the posterior cuff relative to the anterior cuff muscles, which is a reversal of the asymmetric increasing volume of the anterior cuff relative to the posterior cuff muscles seen with concentric GHOA. LEVEL OF EVIDENCE Diagnostic, level III.