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Compliant layer acetabular cups : friction testing of a range of materials and designs for a new generation of prosthesis which mimics the natural joint.

Scholes, S. C. and Burgess, I. C. and Marsden, H. R. and Unsworth, A. and Jones, E. and Smith, N. (2006) 'Compliant layer acetabular cups : friction testing of a range of materials and designs for a new generation of prosthesis which mimics the natural joint.', Proceedings of the I MECH E part H : journal of engineering in medicine., 220 (5). pp. 583-596.

Abstract

Total joint replacements (TJRs) have a limited lifetime, but the introduction of components that exhibit good lubricating properties with low friction and low wear could extend the life of TJRs. A novel acetabular cup design using polyurethane (PU) as a compliant layer (to mimic the natural joint) has been developed. This study describes a series of friction tests that have been used to select the most appropriate material, optimize the design parameters, and fine-tune the manufacturing processes of these joints. To determine accurately the mode of lubrication under which these joints operate, a synthetic lubricant was used in all these tests. Friction tests were carried out to assess the lubrication of four PU bearing materials. Corethane 80A was the preferred material and was subjected to subsequent testing. Friction tests conducted on acetabular cups, manufactured using Corethane 80A articulating against standard, commercially available femoral heads, demonstrated friction factors approaching those for full-fluid-film lubrication with only approximately 1 per cent asperity contact. As the joint produces these low friction factors within less than half a walking cycle after prolonged periods of loading, start-up friction was not considered to be a critical factor. Cups performed well across the full range of femoral head sizes, but a number of samples manufactured with reduced radial clearances performed with higher than expected friction. This was caused by the femoral head being gripped around the equator by the low clearance cup. To avoid this, the cup design was modified by increasing the flare at the rim. In addition to this the radial clearance was increased. As the material is incompressible, a radial clearance of 0.08 mm was too small for a cup diameter of 32 mm. A clearance of between 0.10 and 0.25 mm produced a performance approaching full-fluid-film lubrication. This series of tests acted as a step towards the optimization of the design of these joints, which has now led to an in vivo ovine model.

Item Type:Article
Keywords:Total joint replacement, Polyurethane, Friction, Acetabular cup, Lubrication.
Full text:PDF - Published Version (1237Kb)
Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1243/09544119H06404
Publisher statement:© Scholes, S. C. and Burgess, I. C. and Marsden, H. R. and Unsworth, A. and Jones, E. and Smith, N., 2006. The definitive, peer reviewed and edited version of this article is published in Proceedings of the I MECH E part H : journal of engineering in medicine, 220, 5, pp. 583-596, 10.1243/09544119H06404
Record Created:18 Nov 2008
Last Modified:09 Aug 2011 17:06

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