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Item type:Publication, Access status: without files , Backside wear of tibial polyethylene components is affected by gait pattern: A knee simulator study using rare earth tracer technology(2020-07-01); ; ; ; The aim of this study was to determine the effect of two in-vivo–determined gait patterns, one with low and one with high anteroposterior (AP) motion, on total and backside polyethylene insert wear in comparison with the ISO (International Organization for Standardization) standard 14243-3. In order to differentiate and accurately quantify topside and backside wear, a novel technique was employed where different lanthanide tracers were incorporated into the polyethylene during manufacture. Wear particle analysis was conducted following established protocols. For all tested liners and motion protocols, the chemically calculated wear rates correlated closely with gravimetrically determined wear. Both in vivo motion groups displayed higher wear rates than the ISO group following the order of the AP motion amplitudes. Backside wear for ISO constituted 2.76% ± 0.90% (mean ± SE) of the total wear, increasing significantly to 15.8% ± 3.2% for the low AP and further increasing to 19.3% ± 0.95% for the high AP motion protocol. The mean wear particle sizes were under 200 nm for all three motion patterns, being largest for the protocol with high AP motion. Particle release from the low and high AP gait patterns was 1.9 to 2.8 times that from the ISO protocol. Testing for the proportion of backside wear across various activities of daily living should be an important consideration in evaluating knee prostheses wear.Publicationtype: Journal Article79 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Competitive binding of Bilirubin and Fatty Acid on Serum Albumin Affects Wear of UHMWPE(Multidisciplinary Digital Publishing Institute (MDPI), 2020-05-10); ; ; ; Total Joint Replacement (TJR) devices undergo standardized wear testing in mechanical simulators while submerged in a proteinaceous testing solution to mimic the environmental conditions of artificial joints in the human body. Typically, bovine calf serum is used to provide the required protein content. However, due to lot-to-lot variability, an undesirable variance in testing outcome is observed. Based on an earlier finding that yellowish-orange serum color saturation is associated with wear rate, we examined potential sources of this variability, by running a comparative wear test with bilirubin; hemin; and a fatty acid, oleic acid, in the lubricant. All these compounds readily bind to albumin, the most abundant protein in bovine serum. Ultrahigh molecular weight polyethylene (UHMWPE) pins were articulated against CoCrMo discs in a pin-on-disc tribometer, and the UHMWPE wear rates were compared between lubricants. We found that the addition of bilirubin increased wear by 121%, while hemin had a much weaker, insignificant effect. When added at the same molar ratio as bilirubin, the fatty acid tended to reduce wear. Additionally, there was a significant interaction with respect to bilirubin and hemin in that UHMWPE wear rate decreased with increasing fatty acid concentration. We believe the conformational change in albumin by binding bilirubin makes it more likely to form molecular bridges between UHMWPE and the metal counterface, thus increasing adhesive wear. However, fatty acids compete for binding sites on albumin, and can prevent this conformational change. Hence, the protein is stabilized, and the chance for albumin to form bridges is lowered. Ultimately, UHMWPE wear rate is driven by the competitive binding of bilirubin and fatty acid to albumin.Publicationtype: Journal ArticleScopus© Citations 8 174 211 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Articulation of an alumina-zirconia composite ceramic against living cartilage – An in vitro wear testBackground: There is interest in minimally invasive solutions that reduce osteoarthritic symptoms and restore joint mobility in the early stages of cartilage degeneration. The aim of the present study was to evaluate an alumina-zirconia composite (AZC) as a counterface for articulation against live cartilage explants in comparison to the clinically relevant cobalt-chromium (CoCrMo) alloy. Methods: A four-station bioreactor designed to articulate against living tissue in an incubator was used for testing. Twelve 32 mm AZC and twelve 32 mm CoCrMo femoral heads with equal surface roughness made up both test groups. Each head articulated against a cartilage disk harvested from stifle joints of 24-week old steers. Test samples and free-swelling control cartilage samples were cultured in Mini ITS medium. Testing was conducted 3 h daily over 10 days applying a contact load of approximately 2 MPa. PG/GAG and hydroxyproline were analyzed using biochemical assays. Additionally, chondrocyte survival and Mankin score analyses were performed on histological slides. Results: Cells stayed alive during the course of the experiment, with cell survival values close to 80% at test completion in the superficial zone. There was no significant difference between AZC and free-swelling control tissue. However, cell count values were inferior for CoCrMo (p = 0.003). Tested tissue suffered mostly structural abnormalities. The PG/GAG content in medium was not different between CoCrMo and AZC (p = 0.315); however, the hydroxyproline release into medium was nearly 30% higher for CoCrMo (p = 0.024). Conclusion: Based on average values, AZC induces less cell and tissue damage than CoCrMo. However, only the hydroxyproline measurements reached statistical significance, partially due to substantial scatter within both groups.Publicationtype: Journal Article87 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of molybdate ion and pH on the fretting corrosion of a CoCrMo – Titanium alloy coupleRecent findings suggest that during wear CoCrMo alloys develop a protein-rich protective tribochemical film formed by interaction of released molybdate ion with proteins in the lubricant. The purpose of this study was to determine the effect of adding molybdate ions directly to the medium on the fretting corrosion of a high carbon CoCrMo alloy in contact with a Ti6Al4V alloy. We also examined the effect of lowered pH to simulate acidification that may occur in enclosed areas, as within a modular joint. High-carbon CoCrMo cylindrical pins underwent fretting (± 50 μm, 17 N, 60 MPa) against a Ti6Al4V rod in a flat-on-cylinder configuration in a custom-designed fretting corrosion set-up that included a standard three-electrode configuration for electrochemical measurements. Four electrolytes were used, consisting of diluted bovine serum (30 g/L of proteins), with or without added sodium molybdate (32 mM), and at pH 4.5 or 7.6. All the tests were performed potentiostatically at − 0.25 V versus SCE. Total Co, Cr, and Ti release to the media was determined by ICP-MS. The addition of molybdate ion decreased the release of cobalt by 32% and increased the after-to-before ratio of the polarization resistance by 8 × at pH 4.5, but had not effect on these parameters at pH 7.6. Film deposits in the wear scar were more pronounced in the presence of molybdate ion. The addition of molybdate ion to the medium had a significant protective effect for the CoCrMo only at pH 4.5, possibly because the lower pH allowed for more molybdate-induced protein film formation.Publicationtype: Journal Article105 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A servoelectric apparatus with potentiostat to study the fretting corrosion of cobalt-chromium-titanium alloy couples(ASTM International, 2015); ; ; ; The study of fretting degradation in prosthetic modular junctions requires a combination of tribological testing and electrochemical measurements. The goal of this study was to design a testing apparatus that offers this combination using servoelectric actuator technology because such technology provides ease of installation and handling and is cost-effective. A line-contact configuration that more closely simulates in vivo conditions than the usual point-contact geometry was used. The operation of the apparatus was demonstrated in a study of fretting of a high carbon CoCrMo-Ti-6AI-4V couple. A custom-made fretting corrosion apparatus using a servoelectric universal testing machine (THELKIN, Winterthur, Switzerland) in combination with a standard three-electrode electrochemical system was built. Line contact between the test surfaces was achieved by pressing the flat surfaces of two CoCrMo pins against a vertical Ti-6AI-4V rod attached to the machine actuator. The pins and rod served as the working electrode in an electrochemical cell controlled by a potentiostat. Fretting corrosion conditions were as follows: ±50 μm, 17N normal force, diluted bovine serum (30 g/l proteins) medium at pH 4.5 or 7.6, 5000 cycles test duration, under potentiostatic conditions (-0.25V versus SCE). The servoelectric actuator system was shown not to interfere with the electrochemical measurements. The fretting loops were consistent with a gross slip regime and indicated good system rigidity. The amount of Co and Cr released to the medium was significantly greater at pH 4.5 than at pH 7.6, whereas release of Ti was independent of pH. The reason for the higher wear and corrosion rate of the CoCrMo under acidic conditions appears to be connected with the decreased formation or stability of a chromium-rich protective tribofilm. Significance: A novel fretting corrosion apparatus that goes beyond point contact was constructed and validated to advance the study of fretting degradation in prosthetic modular junctions.Publicationtype: Conference Paper36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Damage due to rolling in total knee replacement : the influence of tractive force© 2013, The author(s). The femoral condyles of a knee prosthesis articulate with a combination of rolling and sliding on the tibial polyethylene plateau. Little is known about potential polyethylene damage due to rolling motion. Since rolling does not exclude the presence of tangential surface loads, this study sought to investigate the influence of tractive rolling on the wear of polyethylene. A “wheel-on-flat” apparatus, consisting of a metal wheel and a polyethylene flat, mimicked contact conditions present in total knee replacement. An increasingly tractive force under conditions of pure rolling was applied. It was found that under rolling kinematics a tangential surface load of up to 17% of the normal load could be transferred through the contact. Surface damage was dependent on the amount of tractive force and appeared more severe with higher forces. In the region of highest tractive force, wear features were identified that resembled perpendicular ridges on surfaces of retrieved tibial polyethylene devices. This suggests that tractive rolling may be a relevant wear mode in total knee replacement.Publicationtype: Journal ArticleScopus© Citations 11 273 254 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , European multidisciplinary consensus statement on the use and monitoring of metal-on-metal bearings for total hip replacement and hip resurfacing(Elsevier, 2013-03-16); ; ; ; Introduction: There is an ongoing debate about the optimal use of metal-on-metal (MoM) bearings in total hip replacement, since there are uncertainties about local and systemic adverse effects due to wear and corrosion of these bearings. Despite various national recommendations, efforts to achieve international harmonization of specific evidence-based recommendations for best practice are still lacking. Hypothesis: An international consensus study group should be able to develop recommendations on the use and monitoring of MoM bearings, preferably at the European level, through a multidisciplinary approach, by integrating the perspectives of various stakeholders. Materials and methods: Twenty-one experts representing three stakeholder groups and eight countries participated in this European consensus study, which consisted of a consensus meeting, subsequent structured discussion, and consensus voting. Results: The current statement defines first of all benefits, local and systemic risks, as well as uncertain issues related to MoM bearings. Safety assessment after implantation of MoM comprises all patients. A closer follow-up is recommended for large head MoM (≥36mm) and resurfacing. In these implants basic follow-up should consist of x-rays and metal ion measurement of cobalt in whole blood, performed with GF-AAS or ICP-MS. Clinical and/or radiographic abnormality as well as elevated ion levels needs additional imaging (ultrasound, CT-scan and/or MARS-MRI). Cobalt values less than 2. μg/L are probably devoid of clinical concern, the threshold value for clinical concern is expected to be within the range of 2-7. μg/L. Discussion: This is the first multinational, interdisciplinary, and multiprofessional approach for developing a recommendation for the use and monitoring of MoM bearings in total hip replacement. The current recommendations are in partial agreement with previous statements regarding the extent of follow-up and imaging techniques. They however differ from previous communications regarding measurement of metal ions and especially the investigated medium, technique, and eventual threshold levels. Level of evidence: Level V, expert opinion/agreement conference.Publicationtype: Journal Article211 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Microstructure of retrievals made from standard cast HC-CoCrMo alloys(ASTM International, 2013); ; ; ; During the past decade, self-mating metal bearings based on cobalt- chromium-molybdenum (CoCrMo) alloys have become very popular in total hip replacements and hip resurfacings. This led to a market share of more than 35 % for metal-on-metal (MoM) bearings in the United States before several cases of high wear with biologic consequences led to a sharp drop in popularity. In part, these failures are a result of a very shallow understanding of the wear mechanisms in MoM joints and their relation to the microstructure. In order to find such a relation, one has to keep in mind that the microstructures of metallic materials depend distinctly on the entire production sequence. In addition, they change markedly under tribological stresses. This paper does not discuss the wear of any specific retrieval or even try to relate that to the specific microstructure, because such a task would be impossible based on the unknown loading history of such retrievals. Thus, we depict only the possible range of microstructures from standardized high carbon (HC)-CoCrMo retrievals. These reveal different types of hard phases: carbides and/or intermetallic phases. Some are fine (<10μm) and homogeneously distributed, whereas others appear as thin (<1 μm) and brittle cord-shaped arrangements at grain or dendrite boundaries. Coarser (>30 μm) types of mixed hard phases, which consist of carbides and interme-tallic phases, often show microcracks already below the articulating surfaces. Such subsurface microcracks are known to destabilize the gradient below the surface and the balance between tribochemical reactions and surface fatigue. In this paper, the microstructures of retrievals manufactured from standard cast CoCrMo alloys are shown and evaluated.Publicationtype: Conference Paper45 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Consensus statement "Current evidence on the management of metal-on-metal bearings" April 16, 2012(Sage Publications, 2013-01-01); ; ; ; The following recommendations are based on expert opinions of an international multidisciplinary panel endorsed by the "European Federation of National Associations of Orthopaedics and Traumatology" (EFORT), the "European Hip Society" (EHS), the German "Arbeitsgemeinschaft Endoprothetik" (AE) and the "Deutsche Arthrosehilfe" (DAH). © 2013 Wichtig Editore - ISSN 1120-7000.Publicationtype: Journal ArticleScopus© Citations 38 27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Metal-on-metal : ion levels as an intervention strategyDue to the wear-related problems with large diameter metal-on-metal THA components, ion levels of cobalt and chromium in blood or serum are used to identify bearings with high-wear rates. Threshold levels for critical concentrations for these two alloys are published and quite frequently revised. Patients and doctors are confused, if measured values are close to thresholds. A new approach is presented by an international expert panel endorsed by EFFORT and several national organizations suggesting the use of a range instead of a specific value as threshold. This approach supports the philosophy that metal ion concentrations by themselves are not a diagnosis but one - important - piece in the assessment of a patient with a metal-on-metal hip articulation.Publicationtype: Journal Article1