Larger-Diameter Trunnions and Bolt-Reinforced Taper Junctions are Associated with Less Tribocorrosion in Reverse Total Shoulder Arthroplasty.

Abstract

Morse taper junction tribocorrosion is recognized as an important failure mode in total hip arthroplasty (THA). While taper junctions are used in almost all shoulder arthroplasty systems currently available in the United States, with large variation in designs, limited literature has described comparable analyses of taper damage in these implants. In this study, taper junction damage in retrieved reverse total shoulder arthroplasty (RTSA) implants was assessed and analyzed. Fifty-seven retrieved RTSAs with paired baseplate and glenosphere components with Morse taper junctions were identified via database query; 19 of these also included paired humeral stems and trays or spacers with taper junctions. Components were graded for standard damage modes and for fretting corrosion with a modified Goldberg-Cusick classification system. Medical records and preoperative radiographs were reviewed. Comparative analyses were performed assessing the impact of various implant, radiographic, and patient factors on taper damage. Standard damage modes were commonly found on the evaluated trunnion junctions, with scratching and edge deformation damage on 76% and 46% of all components, respectively. Fretting and corrosion damage was also common, observed on 86% and 72% of baseplates and on 23% and 40% of glenospheres, respectively. Baseplates showed greater moderate-to-severe (grades≥3) fretting (43%) and corrosion (27%) damage than matched glenospheres (fretting, 9%; corrosion, 13%). Humeral stems showed moderate-to-severe fretting and corrosion on 28% and 30% of implants, respectively; matched humeral trays/spacers showed both less fretting (14%) and corrosion (17%). In subgroup analysis, on glenospheres, large-tapered implants had significantly lower summed fretting and corrosion grades than small-tapered implants (both p≤0.001); paired baseplate corrosion grades were also significantly lower (p=0.031) on large-tapered implants. Factorial analysis showed bolt-reinforcement of the taper junction was also associated with less fretting corrosion damage on both baseplates and glenospheres. Summed fretting and corrosion grades on glenospheres with trunnions (male) were significantly greater than glenospheres with bores (female) (both p≤0.001). Damage to the taper junction is commonly found in retrieved RTSAs and can occur after only months of being implanted. In this study, tribocorrosion predominantly occurred on the taper surface of the baseplate (vs. glenosphere) and on the humeral stem (vs. tray/spacer), which may relate to the flexural rigidity difference between the titanium and the cobalt-chrome components. Bolt-reinforcement and use of large-diameter trunnions led to less tribocorrosion of the taper junction. The findings of this study provide evidence for the improved design of RTSA prostheses to decrease tribocorrosion.