Improving glenoid-side load sharing in a virtual reverse shoulder arthroplasty model

Background The goal of glenoid fixation in reverse shoulder arthroplasty (RSA) is to provide a stable environment to allow bony ingrowth into the baseplate. When this does not occur, eventual baseplate failure is likely. This study aims to determine the additional implant–bone contact achieved when the glenosphere undersurface is in contact with the glenoid and if this increase in implant–bone contact improves stability through load sharing with respect to baseplate fixation. We hypothesize that substantial increases in contact area are possible and that this increased contact area will improve baseplate stability through load sharing. Methods A computer-assisted design program was used to create 3-dimensional models of 7 currently available RSA devices. Total implant–bone contact area was compared in 2 conditions: (1) baseplate flush with bone and no additional glenosphere contact, or (2) baseplate and glenosphere undersurface in contact with bone. Next, finite element models were created from a commercially available system. Micromotion and stress were computed for each size of implant in the 2 conditions. Results All devices tested can achieve increased total contact area when the glenosphere is in contact with bone. Stress and micromotion were reduced when comparing condition 2 with condition 1 in all sizes of one commercially available system. The average micromotion decreased 37%, from 98.04 to 61.97 μm. Larger glenospheres experienced a greater reduction in micromotion. Likewise, average von Mises stress decreased 26%, from 3.29 to 2.42 MPa. Conclusion Increasing glenosphere size and allowing glenosphere undersurface contact increased overall implant–bone contact area and baseplate stability. The goal of glenoid fixation in reverse shoulder arthroplasty (RSA) is to provide a stable environment to allow bony ingrowth into the baseplate. When this does not occur, eventual baseplate failure is likely. This study aims to determine the additional implant–bone contact achieved when the glenosphere undersurface is in contact with the glenoid and if this increase in implant–bone contact improves stability through load sharing with respect to baseplate fixation. We hypothesize that substantial increases in contact area are possible and that this increased contact area will improve baseplate stability through load sharing. A computer-assisted design program was used to create 3-dimensional models of 7 currently available RSA devices. Total implant–bone contact area was compared in 2 conditions: (1) baseplate flush with bone and no additional glenosphere contact, or (2) baseplate and glenosphere undersurface in contact with bone. Next, finite element models were created from a commercially available system. Micromotion and stress were computed for each size of implant in the 2 conditions. All devices tested can achieve increased total contact area when the glenosphere is in contact with bone. Stress and micromotion were reduced when comparing condition 2 with condition 1 in all sizes of one commercially available system. The average micromotion decreased 37%, from 98.04 to 61.97 μm. Larger glenospheres experienced a greater reduction in micromotion. Likewise, average von Mises stress decreased 26%, from 3.29 to 2.42 MPa. Increasing glenosphere size and allowing glenosphere undersurface contact increased overall implant–bone contact area and baseplate stability.