Predicting the wear of hard-on-hard hip joint prostheses

The wear of the bearing surfaces of hip joint prostheses is a key problem causing their primary failure. This paper introduces a wear prediction model with the aid of the finite element analysis. To mimic walking, the most common activity of a human body, a three-dimensional physiological loading gait cycle was considered. The wear at the bearing surface in gait cycles was calculated based on the contact stress variation from the finite element analysis and the sliding distance obtained from three-dimensional hip gait motions. The geometry of the worn surface was updated considering the average routine activities of a patient. The model was applied to three hard-on-hard prostheses, i.e., PCD (polycrystalline diamond)-on-PCD, ceramic-on-ceramic and metal-on-metal couples. It was found that due to the gait motion, the intensity and location of the maximum contact stress in the bearing components change with the gait instances. With a given geometry and gait loading, the linear and volumetric wear on the cup surface increases with the number of gait cycles. With increasing the gait cycles, the surface wear can bring about scattered contact pressure distribution. Compared to the ceramic-on-ceramic and metal-on-metal couples, the PCD-on-PCD bearing has the lowest wear progression. It was also concluded that the computational wear model presented in this paper can reasonably predict the wear evolution in hard-on-hard hip implants.