Finite element analysis of glenoid-sided lateralization in reverse shoulder arthroplasty

The purpose of this study was to evaluate glenoid-sided lateralization in reverse shoulder arthroplasty (RSA), and compare bony and prosthetic lateralization. The hypothesis was that stress and displacement would increase with progressive bony lateralization, and be lower with prosthetic lateralization. A 3D finite element analysis (FEA) was performed on a commercially available RSA prosthesis. Stress and displacement were evaluated at baseline and following 5, 10, and 15mm of bony or prosthetic lateralization. Additional variables included glenosphere size, baseplate orientation, and peripheral screw orientation. Maximum stress for a 36mm glenosphere without bone graft increased by 137% for the 5mm graft, 187% for the 10mm graft, and 196% for the 15mm graft. Likewise, displacement progressively increased with increasing graft thickness. Stress and displacement were reduced with a smaller glenosphere, inferior tilt of the baseplate, and divergent peripheral screws. Compared to bony lateralization, stress was lower with prosthetic lateralization through the glenosphere or baseplate. Displacement with 5mm of bony lateralization reached recommended maximal amounts for osseous integration, whereas, this level was not reached until 10-15mm of prosthetic lateralization. Baseplate stress and displacement in an FEA model is lower with a smaller glenosphere, inferior tilt, and divergent screws. Bony lateralization increases stress and displacement to a greater degree than prosthetic lateralization. It appears that at least 10mm of prosthetic lateralization is mechanically acceptable during RSA, but only 5mm of bony lateralization is advised. (c) 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1548-1555, 2017.