Tensile Stress Analysis of the Ceramic Head Endoprosthesis with different Micro Shape Deviations of the Contact Areas

Abstract

The paper deals with the problems of ceramic head of hip joint endoprosthesis destructions in vivo, and with assessing the impact of shape deflections of conical surfaces on the tensile stress in the head. Concerned are shape deviations from the ideal conical surfaces of the stem and the head of the endoprosthesis. The shape deviations may be modelled at the macro-level - this concerns model shape inaccuracies such as deviation from the nominal degree of taper, at the micro-level - when the stochastic distribution of unevenness on the contact areas is respected. The problem of stress in ceramic heads was solved using the finite element method - system ANSYS under ISO 7206-5 loading. There are presented and analysed the results of solution of the macro shape deviations and micro shape deviations, obtained from measurements made on the cones of stems and heads. There are analysed two different groups of micro shape deviations. The first is three variants of the sizes of the measured micro shape deviations (measured, doubled and halved). The second group of the analysed shapes deviations contained modeled deviations with the linear transformation of the measured deviations along the cone depth.