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Lubrication and Wear of Ultra-High Molecular Weight Polyethylene in Total Joint Replacements
Published September 08, 1997 by Institution of Mechanical Engineers in United Kingdom
Event: New Directions in Tribology
This paper reviews recent advances in tribology of artificial joints. Emphases are given to the latest developments in understanding wear mechanisms and in wear testing of ultra-high molecular weight polyethylene (UHMWPE) materials and components. Two major advances have been made. One is the discovery and recognition of the importance of multidirectional motion in wear mechanisms and wear testing of UHMWPE. The other is the development of an orientation-softening wear concept. The significant of joint kinematics in wear of acetabular and tibial components is discussed. New ways of improving the wear resistance of UHMWPE are proposed based upon the theory of orientation softening. Crosslinking of UHMWPE by ionizing radiation has been shown to significantly improve the wear resistance. The degree of improvement is greater with higher doses of irradiation and is much more effective for the hip than for the knee. A starved lubrication mechanism is proposed for the conforming contact between a UHMWPE acetabular cup and a CoCr or alumina ceramic head. Soluble proteins are found not to be an effective boundary lubricant for UHMWPE. Criteria for validating wear and joint simulator testing are discussed. Focuses are given on the choice of lubricant, the degree of motion and the positioning of components in joint simulator testing.