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Abstract
The most significant clinical problems in patients with total hip replacements (THR) are related to wear of these prostheses and the biological response to wear debris. Three experimental approaches used to understand consequences of wear in THRs are implant retrieval research, in vivo animal models, and in vitro studies. This clinically motivated research investigated mechanisms and implications of wear in alumina ceramic-on-ceramic (COC) THRs using a combination of these approaches. Implant retrieval analysis of 54 COC bearings found posterior edge loading was a normal occurrence in THRs, while anterosuperior edge loading was associated with high wear and persistent squeaking. The architectural features of the pseudocapsules surrounding 23 of these prostheses varied in response to a combination of debris, but there was no evidence tissue inflammation contributed to the THR failure. The acute inflammatory response to alumina nanoparticles was investigated further using a murine air pouch model, in which a variable synovial-like lining of macrophages and multinucleated giant cells phagocytized the nanoparticles. In addition to the air pouch model, a novel xenograft animal model was used to investigate the effects of polyethylene particles generated in patients. These were delivered to a trabecular bone defect in athymic rats via human granuloma tissues where they inhibited bone healing. Each experimental approach had limitations. However, from these multifaceted studies, one can conclude that alumina COC THRs have low wear bearings and are biocompatible, with no evidence of wear-debris related complications, even when edge loading has occurred.