New compounds for improving wear behavior of a tumor knee endoprosthesis

Wear of the central bushing made of ultra-high molecular weight polyethylene (PE-UHMW) of the hinged knee endoprosthesis of a tumour-resection system is the leading reason for revision. The aim of the study was to optimize the wear characteristics of the endoprosthesis on the basis of the tribological properties of new materials and an additional finite element (FE) calculation taking account of the given design. In screening tests the reference combination of PE-UHMW bushing and CoCr axis--used in the clinical setting--was first tested. The PE-UHMW bushing was then replaced by one made of each of the materials reinforced high-density polyethylene (PE-HD) and carbon fibre-reinforced epoxy resin (CFRP). In addition, a new material combination with an alumina ceramic bushing and a CFRP axis was investigated. In comparison with the reference combination PE-UHMW/metal, the combination of ceramic bushing and CFRP axis showed less wear. However, with the particular design of the prosthesis studied here, high mechanical loading applied experimentally resulted in mechanical failure. FE calculations confirmed these experimental results. Improvement of the wear characteristics of this specific implant caused therefore be achieved only by optimizing the bearing design.