Glenoid bone stock and morphology and rotator cuff muscle quality and tendon integrity affect the outcome of total shoulder arthroplasty. We hypothesized that glenoid bone loss correlates with rotator cuff muscle fatty infiltration (FI), tendinopathy, and atrophy.
Forty-three 3D CT scans and MRIs of 43 patients (mean age 62 years; SD 13 years; range 22-77 years) referred for primary shoulder pain were evaluated. Measurements of glenoid bone stock, version, and posterior humeral subluxation index (HSI) were assessed on an axial CT image reconstructed in the true scapular plane. Measurements utilized the Friedman line to approximate the pre-pathologic surface. Glenoid morphology was assigned by modified Walch classification. Rotator cuff FI, atrophy, and tendon integrity were assessed on corresponding MRIs.
There was a very strong negative correlation between increasing glenoid version and HSI (r = - 0.908; p < 0.0001). There was a moderately negative correlation between anterior bone loss and HSI (r = - 0.562; p < 0.0001) and a moderately positive correlation between posterior bone loss and HSI (r = 0.555; p < 0.0001). Subscapularis muscle FI correlated moderately with increased anterior and central bone loss and increased humeral head medialization (r = 0.512, p = 0.0294; r = 0.479, p = 0.033; r = 0.494, p = 0.0294; respectively). Inter-observer reliability (intra-class correlation coefficient [ICC] and kappa) was good to excellent for all measurements and grading.
Glenoid anteversion and anterior and posterior bone loss are associated with varying HSI. Subscapularis muscle FI, not tendon integrity, correlates to anterior and central glenoid erosion. The study adds evidence that neither rotator cuff tendinopathy nor muscle atrophy exhibits a significant relationship to HSI.