Wear and corrosion at modular taper junctions of orthopedic endoprostheses remain of great concern and are associated with adverse clinical reactions. Whereas fretting and corrosion of hip tapers was extensively investigated, there is only little knowledge regarding the clinical performance of modular shoulder prosthesis. This retrieval study evaluated moderately to severely worn taper junctions of anatomical shoulder explants. A total of 30 hemiarthroplasties (n=26) and total shoulder arthroplasties (n=4) of 9 different manufacturers were assessed. The mean service life was 3.1 ± 4.4 year (0.5-22 years), 11 patients were male and 19 were female. Modular humeral heads of ceramic (n=5) or CoCrMo alloy (n=25) have been aligned either with CoCrMo (n= 4) or Ti6Al4V trunnions (n= 26).
All explants were assessed using a stereo-light microscope to examine the locations of material degradation. Selected components were investigated using scanning electron microscopy with energy dispersive X-ray spectroscopy (EDS), confocal microscopy and metallography to determine the damage mode as well as the effects of the taper topography and the alloy microstructure.
Among all examined humeral heads, 83% exhibited prevalence of material degradation that could be associated with potential material loss. We show that oxide films, carbonaceous materials, wear debris as well as corrosion products can accumulate in the contact areas of the stem and head tapers. Based on the determined volumetric material transfer, we found that corundum blasted Ti6Al4V trunnions seem to be more susceptible to severe wear damages independently of the head material than turned CoCrMo or Ti6Al4V trunnions.
This retrieval study confirmed that taper wear and corrosion also occur on less weight bearing implants, like shoulder prosthesis. We assume that the surface defects due to corundum blasting hinder the formation of a stable passivation layer, thereby reducing the pitting corrosion resistance at the taper junction. Further work, however, will be needed to identify of the exact damage pathways.