Mechanics and Performance of Traceable UHMWPE Implants

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DESCRIPTION (provided by applicant): Total hip replacement (THR) surgery is the standard of care for advanced degenerative joint disease. However, 13-18% of all THR surgeries are reoperations, which have poorer outcomes and greater economic burden than primary THRs. Bearing technologies have undergone major changes with respect to formulation and component design over the past decade with the introduction of first-generation highly crosslinked ultra-high molecular weight polyethylene materials (remelted and annealed) and the recent introduction of second-generation materials, stabilized with sequential annealing or vitamin-E diffusion. With the advent of these more wear resistant materials, head sizes have increased to reduce the incidence of instability. Ten years ago, we began a multi-institution traceable retrieval collection to determine in vivo changes to polyethylene components and to analyze periprosthetic tissue responses to polyethylene wear debris. We have developed protocols to measure the mechanical properties, oxidation, and volumetric wear of retrieved implants, as well as the size and shape of polyethylene wear debris and the associated immunologic response through analysis of periprosthetic tissue samples. We now have evidence to show that degradation of gamma inert-sterilized, annealed, and remelted polyethylene occurs in the body for short- to intermediate-term implantation times (<10 years). There is a continued need to understand the long-term effects of in vivo degradation of highly crosslinked polyethylenes and to evaluate the performance of new material and design modifications. Through explant studies we will evaluate: the performance of retrieved annealed and remelted bearings implanted greater than 5 years; the clinical performance of second-generation highly crosslinked liners; and relationships between head size, wear, and rim damage. We hypothesize that: beyond five years of implantation, in vivo oxidation, wear and loosening as reasons for revision of annealed and remelted highly crosslinked liners will not differ; 2nd-generation polyethylene formulations will preserve oxidative stability and mechanical properties comparable to remelted highly crosslinked liners; and femoral head sizes greater than 28 mm will not increase bearing surface wear and rim damage in first and second generation crosslinked liners. Achieving the proposed aims will lead to improved clinical performance of THRs through a better understanding of bearing technology factors and survivorship of polyethylene components. PUBLIC HEALTH RELEVANCE: Bearing technologies have undergone major changes with respect to formulation and component design over the past decade with the introduction of first- and second- generation highly crosslinked UHMWPE materials. A fundamental objective of our device retrieval research is to understand successful implant materials and designs and assess failures through explant, tissue and clinical analysis. Thus, successful achievement of the proposed research will provide essential information on THR implant performance and clinical outcomes, which are needed for informed health care decisions.