Maximizing range of motion of reverse total shoulder arthroplasty using design optimization techniques

Range of motion (ROM) obtained after reverse shoulder arthroplasty (RSA) is an important factor in patient satisfaction and success of the procedure. The optimum RSA design that maximizes ROM is currently unknown. Furthermore, it is unknown if the envelope of motion the RSA is optimized for (overall versus forward elevation planes only) will determine its design. We hypothesized that these were potentially competing objectives (maximizing ROM in frontal elevation planes would require sacrifice in posterior elevation planes), and as a result the optimized designs would differ. The objective of this study was to use computer models and design optimization techniques to determine RSA configurations optimized for either case and compare them in terms of design and performance. Design parameters included glenoid lateralization, humeral lateralization, neck-shaft angle, and inferior offset of the center of rotation (COR) and two different cup depths. All optimized designs maximized glenoid lateralization and inferior offset of the COR. Designs optimized specifically for greater forward elevation plane ROM, however, had slightly higher neck-shaft angles and greater humeral lateralization. In terms of performance, the optimized designs provided 31% to 39% increases in ROM in comparison to that of a representative commercially-available Grammot-style prosthesis. It was concluded that RSA designs optimized for overall versus forward elevation plane ROMs will differ, but both offer improvement over a representative commercially available design, regardless of which ROM region is considered.