Lateralization in reverse shoulder arthroplasty: A review

Reverse shoulder arthroplasty, as originally designed by Grammont, has revolutionized the treatment of rotator cuff arthropathy as well as fractures about the proximal humerus. The original design consisted of glenoid and humeral components with a medialized center or rotation compared to the native shoulder. Long term outcome studies on this design demonstrated high rates of scapular notching as well as significant loss of external rotation. To combat these flaws, prosthesis design has evolved to include the concept of lateralization whereby the center of rotation is moved laterally compared to the Grammont prosthesis via either the glenoid or humeral components. Lateralization via the glenoid component has sought to reduce scapular notching, however, concerns over early loosening have been raised secondary to increasing stress at the glenosphere/glenoid interface. Lateralization via the humeral component has been theorized to improve the mechanics of the remaining rotator cuff and deltoid musculature while avoiding the problems inherent with glenoid lateralization. While limited clinical evidence is available currently to support one design over the other, multiple biomechanical studies have shown improvements in rates of scapular notching and post-operative external rotation for lateralized humeral and glenoid components. Future research should aim to delineate advantages of one design over the other or optimal combinations of the two designs.