Influence of Complex Frictional Heating and Mechanical Stress Effect for Surface Crystalline Structure Change of Zirconia Femoral Head

Abstract

Several clinical reports pointed out that the monoclinic transformation of crystalline structure of zirconia femoral head with clinical service time can cause the changes of surface roughness and mechanical properties. To elucidate the relationship between these surface roughness change induced by phase transformation and UHMWPE socket wear, hip simulator wear tests were performed on total hip prostheses (THP) up to 6 million cycles running. Four groups of different surface monoclinic phase fraction of Kyocera zirconia heads were prepared by aging treatment prior to the wear tests. The surface roughness/ wear rate of zirconia heads with 0, 10, 50 and 80mol% monoclinic phase fraction were 0.009/ 3.8, 0.014/ 3.9, 0.012/ 3.7 and 0.010µmRa/ 3.1mg/million cycles, respectively. These results exhibit that the surface roughness change induced by phase transformation does not significantly influence extent of the generation of UHMWPE debris in Kyocera zirconia /UHMWPE THP system. In contrast, the surface roughness exhibited complex relation with the monoclinic phase fraction and therefore the morphological analysis was performed on the zirconia articulating surfaces