Biomechanical evaluation of a novel glenoid design in total shoulder arthroplasty

The amount of articular curvature mismatch providing optimal performance in total shoulder arthroplasty (TSA) is unknown. The objectives of this study were to quantify glenohumeral joint mechanics before and after TSA and to compare the performance of 3 glenoid components: (1) nonconforming, (2) conforming, and (3) a novel design featuring a conforming center extending into a nonconforming periphery. Six fresh-frozen cadaveric shoulders (mean age, 43 years) were mechanically tested on a custom apparatus by use of simulated muscle forces and a coordinate-measuring machine to determine joint kinematics. B-spline models of the natural and prosthetic articular surfaces were generated, and joint contact was computed by use of a proximity criterion. During both centered (P = .02) and eccentric (P = .05) loading protocols, glenoid contact migrated posteriorly in conforming implants. No statistical differences in kinematics and contact were found among the nonconforming design, the new design, and the natural joint. Therefore, adding a central region of conformity does not compromise the ability of nonconforming TSA components to reduce rim loading.