Rotator cuff tear arthropathy and reverse total shoulder arthroplasty: biomechanics and contemporary designs

Rotator cuff tear arthropathy (RCTA) is a complex condition characterized by rotator cuff insufficiency, altered shoulder kinematics, and progressive joint degeneration. In advanced stages, it results in pain, loss of active elevation, and significant functional impairment. Reverse shoulder arthroplasty (RSA) is now the best surgical option for advanced RCTA because it restores shoulder elevation by changing how the joint works and making the rotator cuff less important. The original RSA concept focused on medialization and distalization of the center of rotation to increase the deltoid moment arm, improve joint stability, and allow active elevation in the absence of a functional rotator cuff. Although this design provided clinical improvement, it also revealed biomechanical limitations, including scapular notching and restricted rotational range of motion, among others. In response, contemporary RSA systems have evolved design modifications, such as lateralization and glenosphere eccentricity, inferior tilt, variable humeral neck-shaft angles, and modular humeral socket configurations. These strategies aim to optimize deltoid efficiency, minimize impingement, and improve range of motion. Despite the availability of numerous implant designs, no consensus exists regarding the optimal combination of components or positioning parameters. A comprehensive understanding of RSA biomechanics associated with modern designs is essential for implant selection and surgical planning in patients with RCTA.