An axisymmetric contact model of ultra high molecular weight polyethylene cups against metallic femoral heads for artificial hip joint replacements

Contact mechanics of ultra high molecular weight polyethylene (UHMWPE) cups against metallic femoral heads for artificial hip joints is considered in this study. Both the experimental measurement of the contact area and the f inite element prediction of the contact radius, maximum contact pressure an d maximum Von Mises stress have been carried out for a wide range of contem porary artificial hip joints. Good agreement of the contact radius has been found between the experimental measurements and the finite element predict ions based upon an elastic modulus of 1000 MPa and a Poisson's ratio of 0.4 for UHMWPE material under various loads up to 2.5 kN. It has been shown th at the half contact angle for all the cup/head combinations considered in t his study is between 40 degrees and 50 degrees under a load of 2.5 kN. The importance of this result has been discussed with respect to the anatomical position of the cup when placed in the body and the selection of a simple wear-screening test for artificial hip joints. The predicted contact radius and maximum contact pressure from the finite e lement model have also been compared with a simple elasticity analysis. It has been shown that the difference in the predicted contact radius between the two methods is reduced for more conforming contacts between the femoral head and the acetabular cup and smaller UHMWPE cup thickness. However, goo d agreement of the predicted maximum contact pressure has been found for al l the combinations of the femoral head and the acetabular cup considered in this study. The importance of contact mechanics on the clinical performanc e of artificial hip joint replacements has also been discussed.