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Royal Leamington Spa, United Kingdom

Kwon Y.-M.,Nuffield Orthopaedic Center | Kwon Y.-M.,Harvard University | Glyn-Jones S.,Nuffield Orthopaedic Center | Simpson D.J.,Nuffield Orthopaedic Center | And 5 more authors.
Journal of Bone and Joint Surgery - Series B | Year: 2010

The presence of pseudotumours, which are soft-tissue masses relating to the hip, after metal-on-metal hip resurfacing arthroplasty has been associated with elevated levels of metal ions in serum, suggesting that pseudotumours occur when there is increased wear. We aimed to quantify the wear in vivo of implants revised for pseudotumours (eight) and of a control group of implants (22) revised for other reasons of failure. We found that the implant group with pseudotumours had a significantly higher rate of median linear wear of the femoral component at 8.1 μm/year (2.75 to 25.4) than the 1.79 μm/year (0.82 to 4.15; p = 0.002) of the non-pseudotumour group. For the acetabular component a significantly higher rate of median linear wear of 7.36 μm/year (1.61 to 24.9) was observed in the pseudotumour group compared with 1.28 μm/year (0.81 to 3.33, p = 0.001) in the other group. Wear of the acetabular component in the pseudotumour group always involved the edge of the implant, indicating that edge-loading had occurred. Our findings are the first direct evidence that pseudotumour is associated with increased wear at the metal-on-metal articulation. Furthermore, edge-loading with the loss of fluid-film lubrication may be an important mechanism of generation of wear in patients with a pseudotumour. ©2010 British Editorial Society of Bone and Joint Surgery. Source

Duncan L.A.,University of Surrey | Labeed F.H.,University of Surrey | Abel M.-L.,University of Surrey | Kamali A.,Smith and Nephew Orthopaedics Ltd. | Watts J.F.,University of Surrey
Journal of Materials Science: Materials in Medicine | Year: 2011

Post-manufacturing thermal treatments are commonly employed in the production of hip replacements to reduce shrinkage voids which can occur in cast components. Several studies have investigated the consequences of these treatments upon the alloy microstructure and tribological properties but none have determined if there are any biological ramifications. In this study the adsorption of proteins from foetal bovine serum (FBS) on three Co-Cr-Mo ASTM-F75 alloy samples with different metallurgical histories, has been studied as a function of protein concentration. Adsorption isotherms have been plotted using the surface concentration of nitrogen as a diagnostic of protein uptake as measured by X-ray photoelectron spectroscopy. The data was a good fit to the Langmuir adsorption isotherm up to the concentration at which critical protein saturation occurred. Differences in protein adsorption on each alloy have been observed. This suggests that development of the tissue/implant interface, although similar, may differ between as-cast (AC) and heat treated samples. © Springer Science+Business Media, LLC 2011. Source

Li C.X.,Smith and Nephew Orthopaedics Ltd.
Surface Engineering | Year: 2010

Extensive researches carried out over the past few years have shown that the novel active screen plasma nitriding (ASPN) technique can be used to treat low alloy steels, stainless steels, tool steels and other steels to achieve identical nitriding effects as the conventional DC plasma nitriding technology. Importantly, the ASPN technique provides the possibilities of treating non-electrical conducting materials such as steel with an oxidised surface and polymeric materials which are unattainable with a conventional DC plasma system. Experimental results presented in this overview further demonstrate that sputtering and deposition play important roles in nitrogen mass transfer in ASPN. In order to achieve a desirable metallurgical response, materials for the active screen and the amount of bias applied to the component have to be considered in applications of active screen plasma processing. The distance between the screen and the component surface also needs to be considered if the components to be treated are placed in a floating potential. © 2010 Maney Publishing. Source

Li C.X.,Smith and Nephew Orthopaedics Ltd. | Hussain A.,Smith and Nephew Orthopaedics Ltd. | Kamali A.,Smith and Nephew Orthopaedics Ltd.
Wear | Year: 2010

Material loss during hip simulator studies is commonly attributed to wear occurring within the bearing surfaces. Potential mass loss from the non-bearing surfaces and its contribution to the overall gravimetric measurement results are seldom mentioned in the literature. In this study, CoCrMo alloy disc samples and resurfacing cups with various surface conditions were immersion tested in serum solution for up to 1200 h. Gravimetric measurement results showed that the static immersion and cleaning induced weight loss for a cup alone could be in the same order of magnitude as a typical hip simulator tested wear loss reported in the literature for a metal-on-metal hip joint. Since in a hip wear simulator the parts to be tested are generally immersed in serum or other physiologically relevant solutions and cleaned periodically before gravimetric measurement, it is highly possible that material loss can also occur from the non-bearing surfaces, affecting the accuracy, repeatability and comparability of hip simulation tested wear results. Accordingly, non-bearing surface conditions and the potential material loss from the non-bearing surfaces have to be considered in designing hip simulator test protocols and in analysing wear results. The results presented in this paper pertain to in vitro wear simulator studies and have little clinical relevance to the performance of any implant in vivo. © 2009 Elsevier B.V. All rights reserved. Source

Li C.X.,Smith and Nephew Orthopaedics Ltd. | Hussain A.,Smith and Nephew Orthopaedics Ltd. | Kamali A.,Smith and Nephew Orthopaedics Ltd.
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine | Year: 2011

In vitro wear data for hip joint devices reported in the literature vary in a wide range from one simulator study to another sometimes for the same type of device tested under identical physiological testing conditions. We hypothesized that non-bearing surface condition of the testing components could be an important factor affecting the simulator wear results. To confirm this hypothesis, fifteen 50mm metal-on-metal hip resurfacing devices with identical bearing specifications were tested in a ProSim hip wear simulator for 5 million cycles. The heads were standard Birmingham Hip Resurfacing (BHR) heads; whilst the pairing acetabular cups were identical to the standard BHR cup except their different back surface conditions, including: (a) off-the-shelf products after removing the hydroxyapatite (HA) coating; (b) semifinished products without HA coating; and (c) purposely-made cups without cast-in beads and HA coating. Results showed that the different back surfaces of the cups used indeed caused significantly large variations in the gravimetrically measured wear loss. We postulated that materials loss from the non-bearing surface of the testing components could contribute to the gravimetrically measured wear loss during a wear simulator test both directly and indirectly. The results presented in this paper pertain to In vitro wear simulator study and have little clinical relevance to the performance of any implant in vivo. © Authors 2011. Source

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