In vivo corrosion and damages in modular shoulder prostheses

Wear and corrosion at taper junctions of orthopaedic endoprostheses remain of great concern and are associated with adverse clinical reactions. Whereas tribocorrosion of hip tapers was extensively investigated, there is only little knowledge regarding the clinical performance of modular total shoulder prostheses. This retrieval study evaluated 35 modular taper junctions of anatomical shoulder explants using stereomicroscopy, confocal microscopy, as well as optical and scanning electron microscopy to determine the damage modes as well as the effects of taper topography and alloy microstructure. Among all humeral head tapers, 89% exhibited material degradation. Different overlapping wear mechanisms were identified such as plastic deformation, adhesive material transfer, microploughing, and fretting damage. Only CoCrMo cast alloy heads showed a susceptibility to electrochemically dominated fretting in comparison to CoCrMo wrought alloy. Moreover, corundum blasted stem tapers show a significantly increased incidence rate for microploughing. To date, this is the most comprehensive study on the damage types of modular taper junctions of anatomical shoulder arthroplasty proving the existence of fretting even on less weight-bearing implants. This study revealed critical fretting factors, such as the surface finish and the alloy type that are essential for the development of countermeasures that avoid any taper corrosion.