Comparative ageing behaviour of commercial, unworn and worn 3Y-TZP and zirconia-toughened alumina hip joint heads

There is a trend today to develop zirconia toughened alumina (ZTA) composites for orthopaedic applications. So far, there is limited data concerning their sensitivity to ageing, especially considering tests performed on implants produced on an industrial scale. Here, complementary tools were used to assess the ageing resistance of ZTA femoral heads. The results were compared to femoral heads processed under the same industrial process with monolithic 3Y-TZP. As expected, monolithic 3Y-TZP implants exhibited significant ageing. In contrast ZTA femoral head showed no sign of degradation even over a period equivalent to that of a human life. The potential impact of coupling effects between wear and ageing is assessed. Monolithic zirconia and ZTA femoral heads were thus first worn in a hip joint simulator, and then aged in autoclave. The kinetics of transformation of the worn monolithic zirconia implants is accelerated while that of worn ZTA femoral heads remains almost unchanged.