There is an increasing recognition that, in the long-term, total joint replacement (TJR) may be associated with adverse local and remote tissue responses that are mediated by the degradation products of prosthetic materials. There has been particular interest in the metallic degradation products of TJR because of the known toxicities of the metallic elements that comprise implant alloys. In this long-term study, metal release, transport, storage and excretion in patients with TJRs habs been investigated. In the current grant period, it has been demonstrated that (1) elevations in serum Ti, Co and Cr can be detected in individuals with well functioning total hip and knee replacements up to 84 months postoperative; (2) the highest Cr and Co levels have been observed in patients with metal-on-metal bearings; (3) passive dissolution from extensively porous coated Co-base alloy femoral stems is not a dominant mode of metal release; rather, fretting corrosion of femoral components at modular junctions is more closely associated with elevations in serum Cr; (4) in patients with TJR and elevated serum metal concentrations, two molecular weight ranges were found to bind Cr (at approximately 70 kD and approximately 180 kD) whereas a single molecular weight range (at approximately 70 kD) was found to bind Ti; (5) following revision surgery for a failed total hip replacement, circulating metal levels diminish, but remain chronically elevated up to 60 months post-revision; (6) Co- and Ti-alloy particulate degradation products, usually from sources other than the bearing surface, commonly disseminate to paraaortic lymph nodes, liver and spleen, particularly in individuals who have had a failed TJR; and (7) the bioreactivity of metal degradation products is governed by its' physiochemical nature and protein adducts: a Cr-containing 180 kD metal-protein complex was the most stimulatory in these studies. This proposal expands on these findings by addressing the following Specific Aims: (1) to quantify metal release in the prospective primary THR study groups which will be 10 to 15 years postoperative, an interval in which complications related to the implant are more prevalent; (2) to prospectively follow patients with Co-alloy metal-on-metal hip replacements to determine the prevalence of metal hypersensitivity in correlation with the serum and urine metal content; (3) to expand the autopsy retrieval program to characterize not: only the systemic distribution of particulate wear debris but also the tissue metal levels and the cellular localization; and (4) to conduct bioavailability and bioreactivity studies of circulating metal-protein complexes which result from corrosion and wear of joint replacement components.
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