Screening Wear Tester Versus Hip Joint Simulator: Results of UHMWPE Sliding Against Different CoCrMo Counterfaces

Abstract

The wear of ultra high molecular weight polyethylene (UHMWPE) articulating against different CoCrMo counterfaces was tested with unidirectional sliding motion using a reciprocating pin on flat machine (RPOF) in accordance with ASTM 732. The results were compared with wear data obtained from the same material combinations using a hip joint simulator (HJS) featuring a multidirectional sliding motion (biaxial rocking motion). There were three CoCrMo surfaces: a forged CoCrMo alloy (ISO 5832-12), which was subjected to an industrial mass finishing treatment, the same alloy with a hand polished surface finish and a CoCrMo coating applied to the forged CoCrMo alloy by magnetron sputtering physical vapour deposition. The results show that the linear reciprocating motion led to a deterioration of the PVD coating causing significantly higher UHMWPE wear compared to the mass finished and hand polished forged CoCrMo alloy. However, the same CoCrMo coating caused significantly less UHMWPE wear than the forged CoCrMo alloys in the HJS. These results highlight the importance of selecting the correct choice of sliding motion, suggesting that this type of coating may be promising for applications in which multidirectional sliding predominates, for example, as a coating on femoral heads in artificial hip joints.