Patients undergoing RSA using a lateralized humerus design with greater inferior overhang of the glenosphere demonstrated significantly greater improvement in aFE and lower rates of notching compared to those with low overhang. No ideal glenosphere overhang range was identified to maximize function in this study.
Using a prospectively collected shoulder arthroplasty database, all primary RSAs performed at our institution between 2007 and 2015 with a single implant design (lateralized humerus, medialized glenoid) and minimum 2-year follow-up were evaluated. Glenosphere overhang in relation to the inferior rim of the glenoid was measured in millimeters (mm) on postoperative Grashey radiographs of the shoulder and categorized into tertiles (low, ≤7.1 mm; medium >7.1 to ≤9.9 mm; high, >9.9 mm). Clinical outcomes of interest comprised of the change between preoperative and postoperative values for the following ROM and outcome score measures: active forward elevation (aFE), active external rotation, the American Shoulder and Elbow Surgeons (ASES) score, the Constant-Murley score (CMS), the Shoulder Pain and Disability Index (SPADI), and the Simple Shoulder Test (SST) score. Random effects linear models were used to assess univariate and multivariable associations between overhang tertile and change in patient outcomes. Differences in outcomes were further compared to the minimal clinically important difference (MCID).
Previous studies have demonstrated that decreased impingement-free range of motion (ROM) can adversely influence clinical outcomes following reverse shoulder arthroplasty (RSA). Inferior placement of the glenosphere is thought to minimize impingement and its associated sequelae. This study evaluates the relationship between inferior overhang of the glenosphere and clinical outcomes in patients undergoing primary RSA using a lateralized humeral implant design.
The study identified 284 shoulders in 265 patients. Median follow-up was 36 months (range, 24-108 months). Median glenosphere inferior overhang was 8.4 mm with an interquartile range (IQR) of 6.3-10.6 mm. Plots demonstrated a non-linear relationship between overhang, outcome scores, and ROM. Patients with a high overhang experienced significantly greater improvements in aFE compared to patients with low overhang (p=0.019) which exceeded the MCID. No other differences in ROM and outcome scores between overhang groups exceeded the MCID. For other outcome scores and ROM measurements, there was no significant relationship with glenosphere overhang. Increased overhang was associated with a significantly lower incidence of scapular notching (p = 0.005).