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Effects of High Dose Irradiation on Cross-Linking of Vitamin E-Blended UHMWPE
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| Vitamin E-stabilized, highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is a promising oxidation and wear resistant UHMWPE with improved mechanical strength in comparison with the first generation, irradiated and melted UHMWPE. However, radiation cross-linking efficiency of UHMWPE decreases in the presence of vitamin E. Therefore an optimum vitamin E concentration and radiation dose level need to be determined to achieve a cross-link density comparable to 100-kGy irradiated and melted UHMWPE, which has shown excellent wear properties in vivo. Vitamin E concentrations equal to or above 0.3wt% (3000 ppm) in blended materials are not recommended for subsequent irradiation to achieve a wear resistant cross-linked UHMWPE. |
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Trace Concentrations of Vitamin E Protect Radiation Crosslinked UHMWPE from Oxidative Degradation
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| This research tested the hypothesis that the oxidation resistance of Vitamin E-blended UHMWPE would be influenced by trace doses of antioxidant, resin, and radiation treatment. Trace concentrations (<=500 ppm w/w%) of alpha-tocopherol (Vitamin E) were blended separately with GUR 1020 and 1050 resins, molded into disks, and irradiated according to different protocols. The results of this experiment supported the hypotheses that trace concentrations of Vitamin E, coupled with radiation treatment-but not resin grade-influence the mechanical and oxidative degradation behavior of UHMWPE. |
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Effects of Packaging on Free Radicals in Vitamin E Blended UHMWPE
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| Ultra-high molecular weight polyethylene (UHMWPE) powder (GUR 1020) was blended with high concentration (20%) of vitamin E (alpha-Tocopherol (alpha-T)) for direct detection of alpha-T radicals in presence of PE radicals. When irradiated in air, alpha-T-resin produced ESR signals characteristics of tochopheroxyl radicals (alpha-T-O(*)), suggesting that PE radicals are quenched by alpha-T. When alpha-T-resin was irradiated in N(2), presence of both PE and alpha-T radicals were evident in the ESR spectra. |
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Assessment of Oxidative Changes after In Vivo Degradation of UHMWPE Knee Components
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| This study reports on the suitability of different experimental techniques to evaluate chemical, microstructural, and mechanical changes associated with in vivo oxidation encountered in historical polyethylene components. The chemical, physical, and mechanical properties data confirmed the occurrence of in vivo degradation in the long-term implanted knee components following gamma irradiation in air. Furthermore, infrared spectroscopy alone appeared to provide excellent insight into the oxidation and crystallization state of the in vivo oxidized polyethylene. |
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2008 AAOS Scientific Exhibit: Gamma Inert Sterilization: A Solution to Polyethylene Oxidation?
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| This study explores the hypothesis that implants sterilized in a low oxygen environment undergo similar in vivo oxidative mechanisms as implants sterilized in air. Over the past seven years, an multi-institutional retrieval program has traced and analyzed 264 conventional polyethylene hip and knee components. Measurable oxidation was observed in all cohorts. The oxidation was regional. Surfaces with access to bodily fluids were more heavily oxidized than protected, bearing surfaces. This variation appeared to be greater in gamma-air sterilized implants. The research therefore demonstrates that gamma inert sterilization may have improved, but not completely solved, the problem of polyethylene oxidation for hip and knee arthroplasty. |
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Correlation of In Vivo Wear and Motion Patterns in TDR
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| This study combined the evaluation of retrieved total disc replacements (TDRs) with a biomechanical study using human lumbar spines. Thirty-eight CHARITE TDRs were retrieved from 32 patients after 7.3 years average implantation. In parallel, 20 new implants were evaluated at L4-L5 and L5-S1 in an in vitro lumbar spine model. This is the first study to directly compare the long-term PE wear and damage mechanisms in TDR retrievals with the motion patterns generated by a validated in vitro cadaveric testing model. The retrievals exhibited wear patterns consistent with the in vitro testing. |
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2008 ORS Poster: Future Young Patient Demand for Primary and Revision Joint Replacement
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| Researchers from Exponent have developed updated nationwide projections for primary and revision TJR for the young patient population in the U.S. Using the most recent procedure data currently available for the U.S., previous projections were updated and the hypothesis was tested that patients younger than 65y will represent the majority (> 50%) of the anticipated demand for primary and revision TJR in the U.S. between 2010 and 2030. While researchers previously forecast a massive demand for primary hip and knee replacement, the current study underscores the major contribution that young patients are expected to play in the future utilization of primary TJR surgery. |
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2008 ORS Poster: In Vivo Oxidation, Oxidation Potential, and Clinical Performance of First and Second-Generation Highly Crosslinked Acetabular Bearings for THA
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| Highly crosslinked polyethylenes were developed to reduce wear in THA and are thermally processed by remelting or annealing. The main hypothesis was that highly crosslinked polyethylene formulations would have lower oxidation, oxidation potential, and lower head penetration than historical gamma-air and conventional gamma-inert sterilized liners. 109 highly crosslinked (90 - 105 kGy) retrieved components were compared with 48 gamma sterilized (25-40 kGy) controls. Penetration measurements were significantly lower in the highly crosslinked groups. Regional variations in oxidation were observed in all groups except for the remelted and sequentially annealed groups. The results of this retrieval study support the hypothesis that highly crosslinked polyethylene reduces in vivo wear, however the oxidation resistance was formulation-dependent. |
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2008 ORS Poster: Immunohistochemical Analysis of Periprosthetic Tissue from THR Revision Surgery
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| Researchers from Drexel University have developed a comprehensive approach to characterizing the specific and non-specific immune response of retrieved periprosthetic tissue from three cohorts of implant devices. Tissue samples were collected from THA revision surgeries of uncemented polyethylene (PE) hip components. The presence of macrophages, T cells, plasma cells and neutrophils was detected in tissue taken from historical, remelted and highly crosslinked polyethylene implants. These data provide the basis for a better evaluation of THR polyethylene-based inflammatory trends. |
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2008 ORS Poster: Polyethylene Particle Load Around Retreived Artificial Discs
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| The purpose of this study was to compare the polyethylene (PE) wear particle load of periprosthetic tissue from total disc replacement (TDR) with results from total hip replacement (THR) at the time of revision surgeries. PE particles were present in TDR and THR tissues, however the load for TDR implants was greater with pre-1998 TDR polyethylene components as compared the post-1998 polyethylene components. This is the first study to demonstrate a quantitative particle load comparison between TDR and THR periprosthetic tissue. |
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2008 ORS Poster: Post Damage in Three Contemporary Designs of Posterior-Stabilized Knee Components
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| The objective of this study was to study the mechanisms of damage at the post in contemporary PS designs and to compare them with the results of a historical gold standard, the IB/PS II. Evidence of damage, usually scratching or burnishing, to the stabilizing post was noted for all of the contemporary PS TKR replacements regardless of the design, similar to the PS IBII components. The extent of post damage was generally mild, and the post was generally not observed to suffer from severe fatigue wear. Wear performance seemed to be insensitive to different designs in all regions. Condylar and post wear for each design followed the general increasing trend with in vivo time, consistent with a fatigue mechanism, while the backside wear was less sensitive to it. |
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2008 ORS Poster: In Vivo Oxidation and Oxidation Potential for Polyethylene in Total Disc Replacement
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| The aim of this study was to investigate the oxidation potential of polyethylene in total disc replacements in the context of the sterilization environment. The main hypothesis was that the rim region of the polyethylene core would exhibit greater oxidation and oxidation potential than the dome. The data support the hypothesis that, for the two types of historical packaging methods employed by the manufacturer, oxidation and oxidation potential were significantly higher at the rim as opposed to the dome. |
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2008 AAOS Poster: In Vivo Oxidation is the Primary Contributor to Delamination in TKA
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| It remains unclear to what extent in vivo oxidation contributes to fatigue wear in TKA. We studied the oxidation profiles in 70 consecutively traced TKA inserts from one manufacturer. Due to their relatively short shelf lives and the significant regional variations between the surface and backsides, oxidation was inferred to have taken place in vivo, supporting our hypothesis that in vivo oxidation is a contributing factor to delamination in TKA. We found no evidence to suggest that in vivo oxidation is related to pitting. Our data also did not support the hypothesis that resin and conversion techniques substantially influence the resistance of tibial inserts to in vivo oxidation. |
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6th Combined ORS Meeting Poster: Validation of Hybrid Model and Ultimate Chain Stretch Criterion for a Second-Generation Highly Crosslinked UHMWPE
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| An analytical model, known as the Hybrid Model (HM), has been shown to accurately capture the large deformation behavior of highly crosslinked UHMWPE. Previous model validation efforts have been focused on predicting the tensile rupture of highly crosslinked materials under uniaxial and multiaxial loading conditions by using the ultimate chain stretch as the underlying theory for failure in polymers. However, it was unknown whether the HM or the ultimate chain stretch criterion would be applicable to second-generation, highly crosslinked UHMWPEs. Consequently, the purpose of the present study was to validate the HM and ultimate chain stretch criterion for a second-generation highly crosslinked material. |
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3rd UHMWPE International Meeting - Polyethylene in Total Joint Replacement Systems: Concerns and Solutions
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| International experts from Europe, the United States, and Asia converged on Madrid for two days of scientific discourse on UHMWPE on September 14-15, 2007. Topics covered at the meeting included in vivo oxidation, Vitamin E, 2nd-generation highly crosslinked UHMWPE, and wear. Transactions of the meeting are now available for download. Speakers at the meeting have been invited to share their presentations via uhmwpe.org, and are made available below individually with the permission of the authors. It was announced that the 4th UHMWPE International Meeting will be organized by Prof. Luigi Costa in Torino, Italy in September 2009. |
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3rd UHMWPE International Meeting Presentation: On the Mechanical Properties of UHMWPE
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| This seminar reviews the mechanical behavior of conventional and highly crosslinked UHMWPE. Methods to more effectively reduce free radicals without having to remelt the material (e.g, doping with vitamin E) have been explored as a means to maintain crystallinity, while simultaneously maintaining better mechanical properties of crosslinked UHMWPE. The combined effects of radiation-induced crosslinking followed by remelting or annealing on mechanical properties of UHMWPE can be complex. Crosslinked materials are found to be more sensitive to notches under uniaxial tensile loading as compared with non-crosslinked UHMWPE, however little difference was found between remelted and annealed UHMWPE materials. |
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3rd UHMWPE International Meeting Presentation: Monotonic and Cyclic Fatigue Behaviors of Conventional and Sequentially Annealed Highly Crosslinked UHMWPE
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| This study examined the effect of notch-induced triaxial stress state on the monotonic and cyclic tensile true stress-strain behavior of conventional and second generation, sequentially annealed UHMWPE. Two geometries of cylindrical dog-bone tensile specimens, smooth and notched, were tested to failure. The materials showed stress hardening and strain hardening in the smooth and notched conditions. Fractographic analysis showed a difference in the fracture micromechanism between the two materials. |
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3rd UHMWPE International Meeting Presentation: Analyses of Oxygen-Induced Radicals in UHMWPE
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| Researchers from the University of Memphis have compiled a review of free radical measurements on UHMWPE following
sterilization with gamma rays (Co-60) at room temperature in open air, vacuum, nitrogen, or argon and subsequently aged at room temperature, 37°C or 75°C for approximately 10 years. Measurements made on vitamin E-mixed UHMWPE powder as well as compression-molded
bulk materials are also presented. Additionally, this report includes data obtained from measurements on retrieved acetabular cups and tibial inserts. All free radical measurements were conducted using X-band (~9 GHz) electron spin resonance (ESR) technique. |
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3rd UHMWPE International Meeting Presentation: Influence of Centrifugation on Morphology of UHMWPE Wear Particles
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| It has been proposed that centrifugation of UHMWPE wear debris at high speeds might influence the shape of the particles. In this study, UHMWPE wear particles were isolated and separated by flotation or centrifugation at (i) 2 min at 500g, (ii) 5 min at 16000g or (iii) 30 min at 105000g. The highest centrifugation speed and time did not influence particle shapes. |
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3rd UHMWPE International Meeting Presentation: Aging of Gamma-Sterilized UHMWPE- Influence of Oxygen Concentration in Barrier Packaging
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| The goal of this study was to evaluate the effect of different barrier packaging combinations on the oxidation and oxidation potential of contemporary gamma sterilized UHMWPE. Accelerated aging was performed on the UHMWPE stored in its packaging at 55°C, corresponding to a ten-fold thermal acceleration for the packaging (ASTM F1980). In contrast with oxidation, which appeared to be insensitive to packaging conditions, the oxidative potential of the material strongly varied with the amount of oxygen present. Small differences in the oxygen concentration within the packaging resulted in large differences in the oxidative potential of gamma inert-sterilized UHMWPE. |
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3rd UHMWPE International Meeting Presentation: Nanoscale Modification of UHMWPE using MPC
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| Investigators from Japan have used photo-induced radical polymerization to graft 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer onto the surface of cross-linked polyethylene (CLPE-g-MPC) in order to reduce friction and wear at the orthopaedic bearing surface. Various grafted poly(MPC) layers 10 to 200 nm thick were clearly observed on the surface of the CLPE substrate. Even after 5.0 x 106 cycles in the hip joint simulator test, no wear of MPC-g-CLPE cups with a poly(MPC) layer 10 nm thick was observed. |
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3rd UHMWPE International Meeting Presentation: Review of Highly Crosslinked UHMWPE Clinical Literature
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| The introduction of highly cross-linked
polyethylene has attempted to solve the problem of increased wear. A detailed review of short-term clinical studies indicates that the volumetric wear of highly cross-linked polyethylene is significantly less than conventional polyethylene. Long-term clinical follow-up is needed to establish the durability of highly cross-linked polyethylene, especially in conjunction with larger diameter femoral heads so as to guide use. |
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3rd UHMWPE International Meeting Presentations: Advances in Wear and Oxidation Resistance of 2nd Generation UHMWPE
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| An alternative second-generation highly crosslinked polyethylene that is irradiated and stabilized by Vitamin-E (alpha-tocopherol) doping has been proposed. Because Vitamin-E stabilization replaces melting, the crystallinity of the irradiated polyethylene is not decreased and hence mechanical properties and fatigue strength are preserved. We investigated the effect of vitamin E presence on the wear and oxidation resistance of acetabular liners. |
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3rd UHMWPE International Meeting Presentation: UHMWPE Stabilization with Vitamin E during E-Beam Irradiation
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| In the present work researchers from Torino have studied both the stability of macroradicals produced during irradiation under inert atmosphere and the thermal stability of hydroperoxides (ROOH) produced
during irradiation in air. The oxidation process induced by e-beam of UHMWPE stabilized with Vitamin E has also been studied. The stabilization effect is a function of the concentration of Vitamin E. These results will be considered in the stabilization process of oxidation of UHMWPE in presence of vitamin E. |
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3rd UHMWPE International Meeting Presentation: Practical Considerations in the Scale Up and Manufacture of Vitamin E-Blended UHMWPE for Orthopedics
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| This study focuses on the results of blending Vitamin E with UHMWPE on a commercial scale. Although blending UHMWPE resins is nothing new in the industrial landscape, it is certainly a challenge when considering the requirements that have become commonplace in producing Medical Grade materials over the last decade.
There is the affect on color, the increased complexity of the process and hence the opportunity to increase inclusions, and finally the new testing and inspection challenges that arise from all of this. |
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3rd UHMWPE International Meeting Presentation: Spectroscopic and Nanoindentation Study of In Vivo Degradation in Total Knee Replacements
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| In the present study, FTIR and Raman spectroscopies, as well as nanoindentation were chosen to characterize oxidative, microstructure, and mechanical changes in gamma sterilized UHMWPE for total knee replacement. Raman spectra performed on surface, subsurface and bulk regions were used to calculate the crystalline content according to Strobl and Hagedorn. This study corroborates in vivo oxidation as the underlying phenomenon responsible for the chemical and microstructure changes, as well as mechanical degradation, in tibial components for total knee replacement. |
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3rd UHMWPE International Meeting Presentation: Ion Implantation of Highly Crosslinked and Remelted UHMWPE
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| Investigators from the University of Zaragoza implanted highly crosslinked and remelted UHMWPE with N and He ions at different ion fluences. Mechanical and tribological properties under distilled water lubrication at body temperature were assessed after ion implantation by means of microhardness and pin-on-disk tests respectively. The influence of the ionic species, and implantation dose on surface hardness, friction coefficient and wear factor were characterized. |
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3rd UHMWPE International Meeting Presentation: On the Novel Use of Nitroxides and Alpha-Tocopherol as Radiolytically-Produced Free Radical Scavengers in UHMWPE
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| Researchers from the University of Maryland have compared alpha-tocopherol (Vitamin E) with nitroxides as electron-transfer radical scavengers. Nitroxides (RRNO) are stable organic compounds that are able to reduce to hydroxylamines and oxidize to oxoammonium cations. These reactions are reversible and can be exploited to yield a novel radical scavenger in UHMWPE. |
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3rd UHMWPE International Meeting Presentation: 15-Year Experience in Analysis of UHMWPE: State of the Art and Future Perspectives
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| During the last 15 years, researchers from Torino have had the opportunity to analyze more than 700 UHMWPE prosthetic components (hip, knee and shoulder). Diffusion of polar compounds from the synovial fluid into polyethylene was observed in the majority of the retrieved samples. The nature of these products have been investigated along with their possible influence on the mechanical properties of the polymer. In the last five years, the researchers have studied a significant number of crosslinked polyethylenes, both new and retrieved. The results of this study indicate that the variables of the crosslinking process can greatly influence final material properties and that not all crosslinked polyethylenes are the same. |
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3rd UHMWPE International Meeting Presentation: Trace Concentrations of Vitamin E Protect Radiation Crosslinked UHMWPE from Oxidative Degradation
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| Our objective was to determine the minimum Vitamin E concentration necessary to protect conventional and highly crosslinked UHMWPE from a severe, in vitro oxidative challenge. Trace concentrations (0-500 ppm) of a-tocopherol (Vitamin E) were blended with GUR 1020 and 1050 resins and compression molded into sheets. 10 mm-thick blocks were divided into three groups: (1) no irradiation (control); 30 kGy of gamma irradiation in nitrogen; and (3) 75 kGy of gamma irradiation in air. The minimum concentration of Vitamin E needed to stabilize UHMWPE during our accelerated tests depended upon the method of radiation processing. |
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In Vivo Oxidation of Gamma-Barrier-Sterilized Polyethylene Bearings
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| Researchers from the Thayer School of Engineering in Dartmouth College have studied polyethylene stored in gamma-barrier packaging before and after implantation. The series of gamma-barrier retrievals studied suggests that oxidation occurs in the body via the same mechanism as seen in gamma-air-sterilized bearings. A critical oxidation level is identified above which polyethylene bearings are susceptible to fatigue damage after sufficient cycles of use. Although critical oxidation was not reached in the majority of the retrieved gamma-barrier bearings studied, in vivo oxidation appears to follow an exponential increase with time. |
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Wear Resistance and Mechanical Properties of Vitamin E Doped Acetabular Inserts
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| Researchers from MGH have evaluated the wear resistance and mechanical behavior of vitamin E-doped, highly crosslinked UHMWPE acetabular inserts. The doped inserts exhibited a four to ten-fold decrease in wear rate from that of conventional UHMWPE. The data indicate good wear properties and improved mechanical and fatigue properties for vitamin-E stabilized cross-linked UHMWPE. |
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Effect of Alpha-Tocopherol on the Oxidation and Free Radical Decay in Irradiated UHMWPE.
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| Researchers have investigated the effect of alpha-tocopherol on the oxidation and transformation of residual free radicals during real-time aging of alpha-tocopherol-doped, irradiated UHMWPE (alphaTPE) and irradiated UHMWPE (control). During the first month, alphaTPE showed some oxidation at the surface, which stayed constant thereafter. Control exhibited substantial oxidation in the subsurface region, which increased with time. In summary, the real-time oxidation behavior of alpha-TPE was consistent with that observed using accelerated aging methods. This new UHMWPE is oxidation resistant and is expected to maintain its properties in the long term. |
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Review of Oxidative Stability, Mechanical Behavior, and Biocompatibility of Alpha-Tocopherol in UHMWPE
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| Recently, alpha-tocopherol (Vitamin E) doped UHMWPE has received increased attention as a novel orthopedic UHMWPE. Alpha-tocopherol doped UHMWPE exhibits excellent wear and fatigue performance and can be applicable to high stress and linear motion applications, such as total knee replacements (TKR). This paper comprehensively reviews recent advances in the mechanical properties, oxidation stability, and biocompatibility of medical grade UHMWPE, particularly focusing on highly crosslinked UHMWPE and alpha-tocopherol doped UHMWPE. |
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Logistics and Implementation of a Multi-Center, Regional Total Hip Replacement Retrieval Program to Investigate In Vivo Oxidation of Polyethylene
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| Researchers have developed a prospective retrieval collection program for specific types of retrieved implants for clinical evaluation and subsequent characterization of mechanical and physical properties. This paper focuses on the logistics and implementation of a multi-center, regional total hip replacement retrieval program to investigate in vivo oxidation of polyethylene. The organizational structure detailed in this manuscript may hopefully be generalized to other multi-institutional retrieval programs that are motivated to answer a specific research question. |
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3rd UHMWPE International Meeting - Polyethylene in Total Joint Replacement Systems: Concerns and Solutions
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| This is the announcement for a two-day meeting in Madrid, which is planned for September 14-15, 2007. The meeting is in two main parts: one basic research module, open for papers and oriented to gather cutting-edge research on UHMWPE; and a second part oriented to clinical aspects and discussion. Additional details about the conference can now be found at the conference website: http://www.facing-bcn.com/uhmwpe2007/. |
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Polyethylene Wear Debris and Long-Term Clinical Failure of the Charite Disc Prosthesis
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| Researchers assessed the clinical significance of polyethylene wear debris in salvage surgery after initial total disc replacement, the pattern and the mechanisms of polyethylene wear in the retrieved cores, and the extent of polyethylene debris in the periprosthetic tissues obtained from 4 patients. All of the retrieved polyethylene cores showed evidence of wear, but the extent and severity varied among the 4 patients. Histologic examination of the periprosthetic tissues confirmed the presence of wear debris lying in inflammatory fibrous tissue. |
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Anisotropy and Oxidative Resistance of Highly Crosslinked UHMWPE after Deformation Processing
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| Solid-state deformation processing is a promising technique for modifying the physical and mechanical properties of highly crosslinked ultra-high molecular weight polyethylene (UHMWPE) beyond simple thermal treatment cycles that have been employed previously. This study evaluates anisotropy and oxidative resistance in a novel, radiation crosslinked (50kGy) UHMWPE material, incorporating solid-state, deformation processing by extrusion below the melt transition for application in total hip arthroplasty. |
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Significance of In Vivo Degradation for Polyethylene in Total Hip Arthroplasty
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| An implant retrieval program was developed to study in vivo degradation of polyethylene. Data from historical, ArCom, and Crossfire retrievals all pointed to a similar scenario in which the femoral head limits the in vivo oxidation of polyethylene at the bearing surface. Researchers concluded that in vivo degradation should be included among the list of potential long-term failure modes for modular polyethylene components for total hip arthroplasty. |
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Digital Photogrammetry for Quantitative Wear Analysis of Retrieved TKA Components
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| Researchers at Drexel University developed a digital photogrammetric method to quantify the extent of surface damage in retrieved total knee replacement components. The overall accuracy of area measurements was 97.8%. The photogrammetry method was found to be reasonably accurate and repeatable in measuring 2-D areas and applicable to determining wear. There was no significant variation in uncertainty detected among different implant designs. |
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Double Notching Apparatus for Impact Testing per ASTM F648 and ISO 5834
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| To faciliate the development of impact testing standards and upcoming round robins, the design drawings and photographs of a double notching device have been provided by Ticona and Orthoplastics. This device is used to reproducibly notch impact test specimens for testing in accordance with ASTM F648 and ISO5834. |
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Oxidation behavior in prosthetic UHMWPE components sterilised with high energy radiation in the presence of oxygen
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| In the present study, a large number of never implanted, gamma sterilised prosthetic components have been analysed by using FTIR micro-spectroscopy and derivatisation techniques. Based on the obtained oxidation profiles, the samples were divided in three groups and a correlation between the oxidation products and distribution and some sterilisation parameters has been proposed. Presence of oxygen, dose rate and temperature were found to play a highly relevant role in determining the whole oxidation degree and its distribution in the UHMWPE components. |
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Book Chapter Excerpt: Total Disc Arthroplasty
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| The state of knowledge in total disc replacements is evolving rapidly. In this field, the majority of published papers are either clinical studies or review articles. This excerpt from the Spine Technology Handbook reviews and examines the previous (and soon to be realized) published technologies behind total disc arthroplasty from a bioengineering perspective. This chapter includes the history and background of CHARITÉ and ProDisc total disc replacements, which both incorporate UHMWPE as a bearing component. |
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Polyethylene Wear and Rim Fracture in Total Disc Arthroplasty
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| The purpose of this study was to evaluate the magnitude and rate of polyethylene (PE) wear and surface damage in TDRs. Twenty-one implants (SB CHARITÉ III: DePuy Spine, Raynham, MA) were analyzed from 18 patients undergoing TDR revision surgery. The dominant wear mechanism was adhesive/abrasive wear at both the dome and rim. This is the first study to quantitatively analyze the long-term PE damage mechanisms in contemporary TDRs. The TDRs displayed surface damage observed previously in both hip and knee replacements. |
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Projections of Primary and Revision Hip and Knee Arthroplasties in the United States from 2005 to 2030
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| This study sought to quantify of the number of primary and revision procedures for total hip and total knee arthroplasty (THA and TKA, respectively) in the U.S. through 2030. Census data were used to incorporate the growth in population through 2030, and a Poisson regression was used to independently model the growth in population and rate of surgeries as a function of age, gender, race, and Census region. Results showed that the total number of revision TKAs performed in 2005 would double by 2015, whereas revision THAs would not double in number until 2026. The projections demonstrate a massive expected future demand for arthroplasty surgeries. |
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An Advanced User Material Model for UHMWPE
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This report summarizes the finite element implementation of the Hybrid Model for UHMWPE as a user-material model in LS-DYNA (http://www.lsdyna.com/). The HM was calibrated to data from uniaxial tension experiments performed at different strain rates and with different loading-unloading segments. For validation, the calibrated HM was then used to simulate a small punch test. A direct comparison between the experimental data and model predictions of the calibration and validation data demonstrate that the HM accurately captures the non-linear response of UHMWPE. The ability to simulate large-scale contact problems was examined by simulating the deformation behavior of a total knee replacement component and the Charité™ artificial disc. |
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Oxidation of Radiation-Sterilized UHMWPE Components in a Low Oxygen Environment
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| In the present study, the early stages of oxidation were investigated by assessing the hydroperoxide levels and distribution within a selection of ready-to-use UHMWPE prosthetic components. Hydroperoxides were detected in all samples, despite the sterilisation in inert atmosphere. Three different types of behaviour were identified and discussed. A correlation with the packaging and sterilisation conditions was proposed. |
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Influence of Remelting on Fatigue Behavior of E-Beam Irradiated UHMWPE
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| Currently used post-irradiation thermal treatments, which aim to decrease the free radicals within the material, introduce microstructural changes that affect UHMWPE mechanical properties, particularly the fatigue strength. This study was planned to evaluate the influence of UHMWPE remelting after irradiation on the fatigue resistance of the material. |
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Effects of Annealing and Remelting on Fatigue Crack Propagation of Crosslinked UHMWPE
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| The objective of this study was to evaluate the effects of gamma radiation-induced crosslinking with two different post-irradiation thermal treatments on the FCP resistance of UHMWPE. Crosslinking was found to decrease the ability of UHMWPE to resist crack inception and propagation under cyclic loading. The findings also suggested that annealing as a post-irradiation treatment may be somewhat less detrimental to FCP resistance of UHMWPE than remelting. |
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Analysis of Retrieved Crossfire Liners
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| This study reports on detailed analyses of retrieved, annealed crosslinked liners. Slight variation in properties was observed as a function of sampling location, with the properties near the unworn surface displaying the greatest relative variability. The authors concluded that the variability in polyethylene properties was not clinically significant. |
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Chemical Co-Agents Enhance Radiation Crosslinking of UHMWPE
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| Researchers from the University of Torino have investigated the effect of unstaturated additives on the crosslinking behavior of UHMWPE. 1,7-octadiene turned out to be the most effective additive for the present purpose, exhibiting a good efficiency in enhancing crosslinking. FTIR analyses showed that consumption of vinyl double bonds is proportional to the irradiation dose, with an efficiency which increases with increasing their initial concentration, confirming the hypothesis of the involvement of these groups in the crosslinking process. |
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Prevalence of Primary and Revision Total Hip and Knee Arthroplasty in the United States
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| The purpose of this study was to quantify the procedural rate and revision burden of total hip and knee arthroplasty in the United States. The number and prevalence of primary hip and knee replacement procedures increased substantially between 1990 and 2002, but the trend was considerably more pronounced for primary total knee arthroplasty. The reported prevalence trends have important ramifications on the number of expected joint replacement surgeries to be performed by orthopedic surgeons in the future. |
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Survey of Oxidation in Contemporary Packaged UHMWPE
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| The packaging and chemical stability of both conventional and highly crosslinked polyethylene components available for clinical use in Italy were analyzed. A total of 100 sterilized polyethylene components were entered by 18 orthopedic manufacturers into the study. This is the first study that relates elevated oxidation and hydroperoxide content in gamma sterilized polyethylene components to certain types of contemporary, polymeric barrier packaging. |
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Crystallinity Changes in Crosslinked UHMWPE During Compression
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| This study examines the effect of a large compressive plastic deformation on the melt temperature (Tm), lamellar thickness, crystallinity, and density of conventional and highly crosslinked UHMWPE. The microstructural evolution during compressive deformation was found to be a function of UHMWPE formulation, as affected by irradiation and postirradation heat treatment. |
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In Vivo Degradation of Polyethylene Liners after Gamma Sterilization in Air
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| The purpose of this study was to quantify the extent to which the mechanical properties and oxidation of conventional polyethylene acetabular liners treated with gamma sterilization in air change in vivo. On the average, the rim and the unloaded bearing showed evidence of severe oxidation near the surface after long-term in vivo aging, but these trends were not typically observed on the loaded bearing surface or near the backside of the liners. |
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Validation of MicroCT Wear Analysis of Hip Replacements
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In this study, a novel microCT based technique for evaluating wear in retrieved acetabular liners was introduced and validated. Overall scanner error was quantified gravimetrically and associated with a maximum uncertainty of 0.6%. Intra- and inter-observer uncertainty analysis showed the method to be both accurate and repeatable. |
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Conference Presentation: Oxidation and Stabilization of Polyethylene
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| This conference presentation describes the rationale for preventing oxidation of polyethylene using synthetic stabilizers, including Vitamin E. This presentation was prepared by Prof. Billingham for a Vitamin E Stabilization meeting at the University of Torino on March 17, 2005. |
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Conference Presentation: Stabilizing Effect of Vitamin E on UHMWPE: Some remarks
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| This conference presentation describes recent findings by the University of Torino related to Vitamin E stabilization of UHMWPE. This presentation was delivered by Dr. Bracco on March 17, 2005, at a Vitamin E stabilization meeting at the University of Torino. |
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Stabilisation of UHMWPE with Vitamin E
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| This paper describes recent findings by the University of Torino related to Vitamin E stabilization of UHMWPE. Vitamin E is found to be an effective and practical stabilizer for preventing oxidation of UHMWPE during consolidation and following irradiation. This paper was presented on March 18, 2005, at the UHMWPE meeting at the University of Torino. |
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Clinical Results of Crosslinked UHMWPE
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| Surgeons from the University of Torino have reviewed the literature describing the clinical performance of crosslinked UHMWPE. This paper was presented on March 18, 2005, at the UHMWPE meeting at the University of Torino. |
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Morphological Analysis of Retrieved Cross-linked UHMWPE and Improved Microstructures for Enhanced Fatigue and Wear Performance
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| This paper discusses the effect of cross-linking on the fatigue properties of UHMWPE and examines the role of cross-linking on clinical performance in total joint replacements. Additionally, this work seeks to examine the role of morphology on the mechanical behavior of UHMWPE and the ability to optimize fatigue and wear behavior with optimized microstructure. This paper was presented on March 18, 2005, at the UHMWPE meeting at the University of Torino. |
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Comparison of the Wear, Wear Debris and Functional Biological Activity of Non-crosslinked and Crosslinked GUR 1020 and GUR 1050 Polyethylenes used in Total Hip Prostheses
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| Researchers from the University of Leeds have characterized the wear and wear particles generated from two different grades of UHMWPE acetabular cups, non-crosslinked GUR 1020 and GUR 1050, moderately crosslinked (4 MRad GUR 1020; 2.5 MRad GUR 1050) and highly crosslinked GUR 1050 (10 MRad) in an anatomical physiological hip joint simulator. The functional biological activity of the wear particles resulting from the wear tests was compared. This paper was presented on March 18, 2005, at the UHMWPE meeting at the University of Torino. |
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New processes to improve the mechanical performance of UHMWPE
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| Researchers from Harvard Medical School report the results of new processing techniques to improve the mechanical properties of crosslinked UHMWPE. The improvements in properties were achieved using high pressure crystallization. This paper was presented on March 18, 2005, at the UHMWPE meeting at the University of Torino. |
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Characterisation of Crosslinked UHMWPE
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| In this review, the test methods used to characterize highly crosslinked UHMWPE are described. This paper was presented on March 18, 2005, at the UHMWPE meeting at the University of Torino. |
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Cross-linked Ultra-High Molecular Weight Polyethylene
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| This review paper describes the radiation chemistry related to highly crosslinked UHMWPE. This paper was presented on March 18, 2005, at the UHMWPE meeting at the University of Torino. |
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Mechanical Properties and In Vitro/In Vivo Oxidation of UHMWPE
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| This review paper compares the distribution of in vivo oxidation in conventional and highly crosslinked UHMWPE implants with oxidation that occurs during in vitro oxidation. This paper was presented on March 18, 2005, at the UHMWPE meeting at the University of Torino. |
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State of the art of UHMWPE in orthopaedics: Sterilisation and packaging
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| In this review, surgeons and researchers from Torino discuss recent observations of oxidation for gamma sterilized prostheses stored in certain types of contemporary packaging. This paper was presented on March 18, 2005, at the UHMWPE meeting at the University of Torino. |
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Microstructure Changes of Extruded UHMWPE After Gamma Irradiation and Shelf Aging
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| Researchers at the University of Zaragoza and Madrid have investigated the lamellar microstructure of ram extruded UHMWPE after gamma irradiation in air and shelf aging using TEM and DSC. The stacking or high lamellar concentration in the subsurface in shelf-aged samples was consistent with higher crystallinity and with a degradation process controlled by oxygen diffusion and free radical distribution after gamma irradiation. |
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Fatigue Resistance of Electron-Beam and Gamma Irradiation Crosslinked UHMWPE
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| Researchers from the University of Zaragoza and Madrid have investigated the fatigue behavior of electron beam and gamma radiation crosslinked UHMWPE. The researchers observed crossover behavior between gamma and electron beam irradiated UHMWPE as a function of the applied stress. |
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Deformation, Yielding, Fracture, and Fatigue Behavior of UHMWPE
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This review paper examines the deformation, yielding, fracture and fatigue behavior of conventional and highly cross-linked medical grade UHMWPE. The mechanical properties discussed include the deformation behavior of UHMWPE, the yielding associated with quasi-static tension and compression, fracture toughness, cyclic loading, and fatigue resistance. |
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Analysis of a Retrieved Total Disc Replacement Component
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In this case study, a detailed retrieval analysis was performed of an explanted Charité disc replacement that was part of the US IDE study. The purpose of this study was to analyze the wear mechanisms, oxidation levels, and mechanical properties of the retrieved polyethylene disc replacement component. Despite the small size of the retrieved polyethylene core, ASTM standard test techniques developed for analysis of retrieved hip and knee replacements were readily adapted for the total disc prosthesis. |
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Fluid Pressure - An Alternative to Wear-Induced Lysis?
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| In addition to polyethylene wear, fluid pressure has been suggested to be an alternative mechanism to producing periprosthetic osteolysis. In this experimental study, the fluid pressure in a screw hole is examined across a range of implant design factors, including polyethylene thickness. |
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Real-Time Shelf Aging Data for Current Sterilization Methods
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| Researchers from the University of Utah have studied the density and oxidation behavior of two UHMWPE materials sterilized by gas plasma, EtO, and gamma irradiation following four years of real-time aging. The type of sterilization method was found to have a larger influence on PE degradation than resin type. |
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Notch Strengthening Behavior of Crosslinked UHMWPE
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This study examined the engineering and true axial stress-strain behavior of smooth cylindrical and shallow and deep notched cylindrical test specimens, under applied axial tensile loading using non-contacting methods, of both conventional and highly crosslinked UHMWPEs. This study suggests that notches inherent in the design of UHMWPE joint replacement components (posts, undercuts, grooves) will have different notch sensitivity depending on the UHMWPE formulation. |
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Molecular Chain Stretch as Multiaxial Failure Criterion
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This paper outlines the theoretical framework for predicting the failure of UHMWPE under uniaxial and multiaxial loading conditions. Out of eight failure criteria evaluated in this study, the maximum molecular chain stretch criterion was found to most closely predict the failure of conventional and highly crosslinked UHMWPE. |
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Failure Property Distributions for Crosslinked UHMWPE
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The goal of this study was to evaluate parametric and nonparametric statistical approaches to describing the failure properties of UHMWPE. Both Normal and Weibull models were found to provide a reasonable description of the central tendency of the failure property distributions for conventional and highly crosslinked UHMWPE. |
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FDA Panel Unanimously Approves Total Disc Replacement
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The orthopedic and rehabilitation devices panel of the U.S. Food and Drug Adminstration unanimously approved the first total disc replacement on June 2, 2004, subject to certain conditions. Although UHMWPE has been used since the 1980s for disc replacement in the spine in Europe, these devices have been only available for investigational use in the United States. |
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Interlaboratory Study of Impact Strength for UHMWPE
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| The purpose of this study was to evaluate the repeatability and reproducibility of a miniature (4 mm) IZOD test specimen method to quantify the impact resistance of UHMWPE stock materials that are too small for production of a standard-sized specimen. The analysis was performed to assist the ASTM committee for F648 in identifying miniature specimen test methods suitable for characterizing the impact strength of consolidated UHMWPE materials. |
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NMR Analysis of Copolymer Content and Branching in UHMWPE Resin
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| Samples of UHMWPE resin were analyzed using 1H NMR to quantify the co-polymer content and branching. The analysis was performed to assist the ASTM committee for F648 in identifying test methods suitable for characterizing the molecular structure of UHMWPE resin materials. |
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Alpha-Tocopherol (Vitamin E) Doped Highly Crosslinked UHMWPE
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Researchers from MGH in Boston have investigated highly crosslinked UHMWPE doped with alpha-Tocopherol (Vitamin E). The researchers observed that the biocompatible antioxidant improved the oxidation resistance, wear resistance, and fatigue resistance of 100kGy-irradiated, highly crosslinked UHMWPE. |
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Effect of Joint Loading on Clinical Wear
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| In this clinical wear study, researchers from the University of Chicago investigated the effect of joint loading on the measurement of radiographic wear. Using the Martell computerized radiographic wear technique, 78 paired AP pelvis radiographs in 46 patients at a mean of 14 months after surgery (range 1-92 months) were evaluated with and without joint loading. |
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Effects of Contact Area and Stress on Wear of UHMWPE
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The effects of contact area and contact stress on the wear of ultrahigh molecular weight polyethylene articulating with a polished surface of cobalt-chromium alloy were evaluated using a pin-on-disk apparatus implementing bi-directional movement. Within a relevant range of contact stress, volumetric wear rate increased with increasing contact area. |
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Rheology of Joint Fluid in Total Knee Arthroplasty Patients
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While the properties of joint fluid may affect the tribology of joint replacement
prostheses, the flow parameters of joint fluid have not yet been examined in the context of total knee arthroplasty (TKA). The objective of this study was to evaluate the flow properties of joint
fluids in patients undergoing index TKA or revision TKA. |
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NIH Draft Consensus Statement on Knee Replacement
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The National Institutes of Health has published a Draft Consensus statement for total knee replacement (TKR) in the United States. This statement reflects the current scientific knowledge regarding TKR, as reviewed at a consensus development conference on Dec 8-10, 2003. |
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Two-Year Clinical Results for Highly Crosslinked UHMWPE in THA
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Researchers from the University of Chicago report the two-year results for a prospective randomized trial comparing highly crosslinked to standard polyethylene in total hip replacements. A significant reduction in two and three-dimensional linear wear rates (42 and 50 percent) was found in the highly crosslinked group. |
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Fractography of UHMWPE Following Accelerated Aging
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| In this study, researchers from Zaragoza and Madrid have explored the fractography of molded GUR 1050 that was gamma sterilized in air and then followed by different aging times at 120 ºC. The microstructure of the UHMWPE from the oxidized zone of the specimens was similar to that found in gamma irradiated tibial components, which had been shelf-aged for 6-7 years. |
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Fracture Behavior of Shelf-Aged Tibial Components
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| Researchers from Zaragoza and Madrid have studied the fracture behavior of UHMWPE knee components that were shelf aged in air for 6 to 7 years following sterilization. Mechanical measurements and fracture morphology in the subsurface region confirmed the embrittlement of oxidized UHMWPE. |
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High Pressure Crystallization of Crosslinked UHMWPE
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Researchers from Brigham & Women's Hospital and Berkeley have developed high pressure processing techniques for highly crosslinked UHMWPE, marrying the fatigue resistance obtained from high pressure crystalization with the wear resistance obtained from crosslinking. This paper was presented on Sept. 19, 2003, at the UHMWPE meeting at the University of Torino. |
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Biological Response to Wear Debris
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| Researchers from the University of Leeds have summarized their research to determine the functional biological activity of in vitro-generated wear debris particles. This paper was presented on Sept. 19, 2003, at the UHMWPE meeting at the University of Torino. |
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UHMWPE Processing: Techniques and Problems
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In this review, Mark Allen from Perplas Ltd. (Bacup, England) provides a coverter's perspective of the challenges related to processing of UHMWPE. This paper was presented on Sept. 19, 2003, at the UHMWPE meeting at the University of Torino. |
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Historical Review: Discovery of Polyethylene
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This paper provides an intimate and detailed account of the historical development of polyethylene, including UHMWPE. This paper was presented on Sept. 19, 2003, at the UHMWPE meeting at the University of Torino. |
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Oxidation and Stabilization of UHMWPE
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Researchers at the University of Turino have written a review summarizing the mechanisms of oxidation and stabilization of UHMWPE using Vitamin E. This paper was presented on Sept. 19, 2003, at the UHMWPE meeting at the University of Torino. |
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Simulation of Unloading and Cyclic Loading
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| A previously developed hybrid constitutive model has been augmented to allow also for accurate predictions of the unloading behavior of conventional and highly crosslinked UHMWPE during cyclic loading. It is shown that the augmented hybrid model accurately captures the experimentally observed characteristics of uniaxial cyclic loading, large strain tension, rate-effects, and multiaxial deformation histories. |
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Mechanical Property Degradation Following Long-Term Implantation
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| In this study, researchers evaluated 16 consecutive traceable Hexloc acetabular components implanted on average 11.5y. The results of this study strongly support the hypothesis that the degradation of mechanical properties for the liners occurred during implantation. |
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Failure Micromechanisms in Conventional and Highly Crosslinked UHMWPE
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| The goals of this study were to evaluate the micromechanisms of failure under uniaxial tension and to determine the effect of gamma radiation-induced crosslinking and post-irradiation thermal processing on the estimated fracture toughness (Kc) of UHMWPE. Reseachers observed the same basic failure mechanism for all of the conventional and highly crosslinked UHMWPE specimens. |
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Comparison of Annealed Crosslinked and Conventional UHMWPE
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| This paper reviews the choices available to an implant designer when developing a highly crosslinked UHMWPE as an orthopaedic bearing material. The authors suggest that the application of annealing rather than remelting in the thermal processing step allows the retention of important mechanical properties in the finished material. |
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Validation of Wear Simulation Methods
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| In this doctoral dissertation, O. Calonius evaluates a range of wear simulation methods for UHMWPE used in joint replacements. Click here to view the abstract page. The entire dissertation is published as an issue of Acta Polytechnica Scandanavica, but the first chapter and overview of wear particle analysis and slide track analysis can be downloaded as a separate pdf here. |
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Prediction of Multiaxial Mechanical Behavior for Conventional and Highly Crosslinked UHMWPE
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| This study compares the predictive capability of the new Hybrid constitutive model with the J2-plasticity model for four conventional and highly crosslinked UHMWPE materials during multiaxial loading. The Hybrid model outperforms the J2-plasticity model both for combined uniaxial tension and compression predictions and for simulating multiaxial large deformation mechanical behavior produced by the small punch test. |
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Multiaxial Fatigue Behavior of Crosslinked UHMWPE
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| The goal of this study was to evaluate the suitability of the small punch test for conducting miniature-specimen, cyclic loading experiments of conventional and highly crosslinked UHMWPE. Fatigue failures were consistently produced according to a power law relationship in the low cycle regime, corresponding to failures below 10,000 cycles. |
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Taguchi Analysis of Accelerated Aging Conditions for UHMWPE
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Using a Taguchi approach, this study documents the effects of heating rate, sample preparation, humidity, test temperature, and the irradiation-aging time interval on the effects of oxidation in UHMWPE after accelerated aging in an oxygen bomb. Accelerated aging results are compared with data collected from samples naturally aged for 3 and 5 years. |
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Interaction of Oxidation and Crosslinking
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The interaction between oxidation and crosslinking in gamma-irradiated ultrahigh molecular weight polyethylene with or without artificial aging was evaluated in this study. The results suggest that the storage environments and durations prior to irradiation and prior to artificial aging must be taken into account in attempting to duplicate the oxidation-crosslinking profiles that occur with actual implants in clinical use. |
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Effect of Natural and Accelerated Aging on Inert-Packaged UHMWPE
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Researchers from Queen's University at Belfast have investigated the effect of shelf storage for 3 years on inert-packaged UHMWPE after gamma irradiation. Gamma-irradiation of vacuum packaged UHMWPE promotes a degree of cross-linking and seems to reduce the susceptibility of gamma-irradiated UHMWPE to oxidative degradation upon removal from its vacuum packaging. |
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Implant Wear in Total Joint Replacement
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The American Academy of Orthopedic Surgeons (AAOS) has published a book reviewing the clinical, biological, design, and material factors influencing wear in total joint replacements. Edited by T.M. Wright and S. Goodman, Implant Wear was based on a symposium convened by the AAOS and the National Institutes of Health in October 2000. All 25 chapters of the book can be downloaded from the AAOS website in pdf format. |
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Thermomechanical Behavior of Crosslinked UHMWPE
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Three series of uniaxial tension and compression tests were conducted on two conventional and two highly crosslinked UHMWPEs. The data collected in this study will be used to develop constitutive models based on the physics of polymer systems for predicting the thermomechanical behavior of conventional and crosslinked UHMWPE used in total joint replacements. |
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Deconvolution of Surface Topology in Crosslinked Acetabular Inserts
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Quantitative analysis of surface morphology is crucial for the comprehensive evaluation of wear surfaces for crosslinked UHMWPE acetabular inserts after short-term implantation, when machining marks may be partially worn away or plastically deformed in vivo. The goal of this study was to provide a unified conceptual framework for discriminating between waviness and roughness of the articulating surface for machined orthopedic components. |
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Effect of Resin, Processing, and Radiation Environment on Mechanical Degradation
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The resin and processing route have been identified as potential variables influencing the mechanical behavior, and hence the clinical performance, of UHMWPE orthopaedic components. In this study, a series of accelerated aging experiments were conducted to systematically examine the influence of resin (GUR or 1900), processing method (bulk compression molding or extrusion), and sterilization method (none, in air, or in nitrogen) on the mechanical behavior of UHMWPE. |
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Virgin UHMWPE is Not Immune to Oxidative Degradation
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Thermal degradation alone, in the absence of free radicals, may be sufficient to artificially age UHMWPE in a manner analogous to natural aging. In the present study, virgin and air irradiated UHMWPE (extruded GUR 1050 and compression molded 1900) were aged up to four weeks at elevated oxygen pressure and the mechanical behavior at the surface and subsurface was examined. |
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Microabrasion to Assess Surface Degradation of UHMWPE
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Thermal degradation alone, in the absence of free radicals, may be sufficient to artificially age UHMWPE in a manner analogous to natural aging. In the present study, virgin and air irradiated UHMWPE (extruded GUR 1050 and compression molded 1900) were aged up to four weeks at elevated oxygen pressure and the mechanical behavior at the surface and subsurface was examined.Researchers from the Queen's University of Belfast have studied the microabrasive properties at the surface of sterilized and aged UHMWPE components. Microabrasion was found to be a sensitive technique for assessing the surface degradation of UHMWPE. |
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Numerical oxidation model for gamma radiation-sterilized UHMWPE
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Researchers have developed a quantitative theoretical model for heterogeneous oxidation in UHMWPE. The predictive capability of the model has been illustrated by simulations of shelf aging in air and accelerated aging at elevated oxygen pressures. |
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Macro- and Microscopic Evaluation of Fatigue in Medical Grade Ultrahigh Molecular Weight Polyethylene
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In this doctoral dissertation, D. Baker evaluates the initiation and propagation of flaws in conventional and highly crosslinked UHMWPE. Of particular interest is a novel form of ultra small angle x-ray scattering, which highlights the fatigue initiation process in conventional and crosslinked UHMWPE. |
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Oxidation of Ethylene Oxide Sterilized Cups
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Retrieved EtO sterilised acetabular cups usually show less degradation than gamma-ray sterilised cups. Some retrieved EtO sterilised cups have, however, revealed unexpected bulk oxidation. In this study, which will be published in a future issue of Biomaterials, researchers from Turin, Italy, examined a mechanism of oxidation in EtO sterilised acetabular cups after long-term shelf aging and implantation. |
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Validation of Oxidation Index Standard after Severe Oxidation
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Researchers have investigated whether severe oxidation associated with long-term shelf aging affects the repeatability and reproducibility of oxidation index measurement techniques. This study, which will be published in a future issue of Applied Biomaterials, provided validation of standard oxidation index measurement methods after severe oxidation. |
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New Hybrid Constitutive Model for UHMWPE
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A new constitutive model has been proposed for the mechanical behavior of UHMWPE under monotonic and cyclic loading histories. This "hybrid model" is the latest addition to a family of physically-inspired constitutive theories for polymers, which incorporate viscoplasticity, as well as viscoelasticity, based upon fundamental, statistically-based deformation mechanisms in polymers. |
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Miniature Specimen Shear Punch Test for UHMWPE
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A miniature specimen (0.5 mm thickness x 6.4 mm diameter) shear punch test has been developed to evaluate the shear behavior of UHMWPE used in total joint replacement components. In this paper, to appear in Biomaterials, researchers have investigated the shear punch behavior of virgin and crosslinked stock materials, as well as of UHMWPE from tibial implants that were gamma-irradiated in air and shelf aged for up to 8.5 years. |
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Wear Surfaces of Highly Crosslinked Acetabular Components
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Highly crosslinked acetabular components have been clinically introduced in an effort to reduce volumetric wear rates and concomitantly the rate of late-onset osteolysis. In this report, researchers examined the wear surfaces of three highly crosslinked acetabular components using optical microscopy, scanning electron microscopy, and white light interferometry. |
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Development of the Small Punch Test for UHMWPE
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This book chapter, made available here with permission of Trans Tech Publications Ltd, traces the historical development of the small punch test and reviews recent research on miniature specimen mechanical test methods for characterizing UHMWPE used in orthopedic components. |
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