Publications & Reports

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5th UHMWPE International Meeting Presentation: Crack Propagation Behavior in HXLPE

The Paris relationship estimates the fatigue crack propagation (FCP) resistance of UHMWPE, but recent studies suggest that a static mode mechanism governs fatigue crack propagation in UHMWPE. The hypothesis of this study is that fatigue crack propagation velocity in crosslinked UHMWPE is driven by the peak stress intensity, Kmax, during cyclic loading, rather than the stress intensity factor range, ΔK. The results suggest that, although crosslinked UHMWPE is a ductile polymer, the fracture mechanisms governing crack propagation are primarily static mode in nature, which is characteristic of brittle materials.

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5th UHMWPE International Meeting Presentation: Properties of an Easily Crosslinkable PE

The aim of this study was to investigate the mechanical properties, fatigue (FCP) and wear resistance for an easily crosslinkable polyethylene with an Mw of 500 kg/mol. The introduction of extra pendant vinyl groups via diene copolymerization did increase the crosslink efficiency significantly.

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5th UHMWPE International Meeting Presentation: The Role of Retrieval Analysis

This invited lecture explores the role of retrieval analysis in the validation of new polyethylenes. Implant retrieval analysis is a major tool in understanding the natural history of UHMWPE THR component behavior. Because clinical screening tools for evaluating in vivo performance of TKR, retrieval analysis is the primary tool for validating UHMWPE TKR component behavior in patients. Implant retrieval analysis has been a valuable approach that has helped to understand the performance of UHMWPE components.

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5th UHMWPE International Meeting Presentation: Tradeoffs in Crosslinked UHMWPE

In this invited lecture, Prof. Lisa Pruitt from Berkely evaluates the wear, fatigue, and oxidation behavior of a large number of clinically-relevant first and second generation ultra-high formulations which may have application in TJA. There is a trade-off amongst wear rate, resistance to fatigue crack propagation, and oxidative stability in clinically-relevant cross-linked formulations of UHMWPE. Moderately crosslinking re-melted materials produces good fatigue and oxidation resistance but fair wear resistance; submelt annealing highly cross-linked materials produces good wear and fatigue properties but leaves the material susceptible to oxidation.

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5th UHMWPE International Meeting - Final Conference Proceedings Posted Online!

The finalized conference proceedings book (99 pp) can now be downloaded for the 5th UHMWPE International Meeting, which was convened at Drexel University, Philadelphia, PA, USA, on September 22-23, 2011. The PDF proceedings include the program and the hyperlinked one- to two-page abstracts for 27 podium and 31 poster presentations. The focus of the present meeting was on clinical, radiographic, and retrieval studies of highly crosslinked UHMWPE, with a special emphasis on the performance of knee arthroplasty; advances in Vitamin E and antioxidant technologies for UHMWPE; structural composites and woven fiber applications of medical grade UHMWPE; advances in biologic aspects of UHMWPE wear debris. We received a record number of abstracts for this meeting.

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5th UHMWPE International Meeting Presentation: Regulation of UHMWPE Biomaterials in Total Joint Arthroplasty

This invited lecture reviews the regulatory pathway for UHMWPE biomaterials for total joint replacement. Dr. Michael Kasser from the FDA starts with an overview of the FDA regulations as they apply to orthopaedic implants. The 510(k) Flowchart is used to illustrate the regulatory pathway for irradiated and thermally treated HXLPEs, as well as the latest generation of HXLPEs containing Vitamin E. The testing requirements that have been required for the FDA to reach a substantial equivalent determination for Vitamin E blended UHMWPEs are outlined in detail.

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5th UHMWPE International Meeting Presentation: In Vivo Oxidative Stability of 1st and 2nd Generation HXLPEs

The purpose of this multicenter study was to assess the oxidative stability, mechanical behavior, wear and reasons for revision of 2nd generation HXLPEs and compare them to our ongoing retrieval collection of 1st generation annealed and remelted HXLPEs. Hip liners were consecutively retrieved during revision surgeries at 10 surgical centers and continuously analyzed over the past 10 years in a prospective, multicenter study of THA revision outcomes and retrieval analysis. All of the HXLPEs materials in this study were effective at reducing wear rates compared to the Gamma Inert and Gas Sterilized controls. The oxidative stability and mechanical behavior of these materials, however, was formulation dependent.

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5th UHMWPE International Meeting Presentation: Surface Damage and In Vivo Oxidation of HXLPE in TKA

The purpose of this study was to investigate the damage mechanisms and oxidative stability of remelted polyethylenes in a consecutive series of retrieved tibial components. Posteriorly stabilized tibial components were retrieved at consecutive revision surgeries at 7 different surgical centers. Remelted highly crosslinked polyethylenes proved to have reduced oxidation indices as compared with conventional inserts.

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5th UHMWPE International Meeting Presentation: In Vivo Performance of Highly Cross-linked UHMWPE

Preliminary in vitro accelerated aging tests have shown that both generations of highly cross-linked polyethylene are vulnerable to oxidation in varying degrees after exposure to lipids. These results raise concerns about the long-term in vivo oxidative resistance of highly cross-linked liners, leading researchers at MGH to investigate the effect of lipid absorption in retrievals. Detectable oxidation has been identified in both 1st and 2nd generations of highly cross-linked retrievals, including both materials with and without free radicals. No other material properties appear to be affected by the oxidation levels at the short- to mid-duration in vivo service times. Investigation of longer duration retrievals will be necessary to determine if this loss of oxidative stability should raise concerns about the longterm clinical performance of these materials.

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5th UHMWPE International Meeting Presentation: Oxidation of Highly Cross-linked Tibial Inserts

In this retrieval study, researchers from Dartmouth University investigated the following hypotheses: (1) highly cross-linked UHMWPE bearings produced by all protocols have the potential to oxidize in vivo, and (2) annealed highly cross-linked UHMWPE has a greater potential to oxidize in vivo than remelted highly cross-linked UHMWPE. Differences in postirradiation thermal processing of highly cross-linked UHMWPE were shown to lead to differences in oxidation resistance of HXL bearings in vivo.

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