In endoprosthesis surgery there are typically a high percentage of implant defects, these can lead to failure of the whole prosthesis. One type of total hip replacement function loss is acetabular cup loosening from the pelvic bone. This article examines manufacture perturbations as one of the possible reasons for this kind of failure. Both dimension and geometry manufacturing perturbations of ceramic head and polyethylen cup were analyzed. We find that perturbations in the variables analysed here affect considered values of contact pressure and frictional moment. Furthermore, contact pressure and frictonal moment are quantities affecting replacement success and durability. From obtained results we can recommend to fit head and cup with a clearance of between 0 mm andd 0.05 mm. We do not recommend using interference type of fit. Roundness perturbation of ceramic head should not exceed 0.025 mm. and Obsahuje seznam literatury
This article studies several aspects of problems associated with diseases of big joints. It is an introductory essay to another three articles that focus on solving various biomechanical problems in hip joint. Stress limit states on contact surfaces of the hip joint can be considered as a common denominator of all these problems. General analyses of these states are described in a separate part of this article. Other general analyses concern the complex of problems associated with diseases of big joints. As an illustration (in view of the articles that follow), this article includes a systemic conception on analysis of the applicability of biomechanics in solving therapeutic problems of big joints. As an illustrative example, the hip joint was selected. and Obsahuje seznam literatury
This article deals with determining the size of linear wear of acetabulum of total hip endoprosthesis by experimental modelling. The creation of an experimental sample and the equipment to simulate human walking are described in detail. The greatest attention is paid to the method form determining the topography of polyethylene cup and measuring of the loss of polyethylene during the simulation of walking. Holographic interferometry was selected to determine the loss of polyethylene cup on the basis of extensive analysis. Further parts of the article focus on first experience with the application of this method results and other possibilities. and Obsahuje seznam literatury
The paper deals with the problems of ceramic head of hip joint endoprosthesis destructions, and with assessing the impact of shape deflections of conical surfaces on the probability of this failure. Concerned are shape deflections from the ideal conical surfaces of the stem and the head of the endoprosthesis, which - when the head is put on the stem and the endoprosthesis loaded - form a contact configuration. The shape deflections may be modelled at the macro-level - this concerns model shape inaccuracies such as deflection from the nominal degree of taper, ovality, and their combination, or, possibly, 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 algorithm of the finite element metod for spatial contact tasks, and the Weibull probability model was used for solving the problem of head cohesion failure probability. In the paper are presented and analysed the results of solution of the micro-level shape deflections, obtained from measurements made on the cones of stems and heads.
The paper is focused on computational modeling of elbow articulation with radial head replacement. The main part of the project is aimed towards the creation of computational model of suitable partial endoprothesis of proximal part of the radial bone tissue which would keep the function of the elbow articulation while replacing the distance created by resection. The geometrical and computational models of radial head replacements and elbow joint were created. Computational models with these implants were compared with given physiological state of elbow articulation. The influence of friction and material characteristics of bone tissue and cartilage on changes in contact pressure (and therefore to the abrasion) were analyzed using those models. and Obsahuje seznam literatury
Possibility of substituting the affected hip joint with endoprothesis is - for many people all over the world - the only way for returning to the normal life without pains and significant motion limitations. But the age limit requiring the application of replacement becomes lower and lower. The endoprothesis applied to young patients must be replaced several times during their lives and the application and repeated replacements affect the bone so that it may happen that the next application may not be possible any more. For such cases the surface replacement the propose of which is to postpone the need of the first application of the classic total endoprothesis, has been invented. So that the objective of the contribution consists in creating a computing model of the healthy hip joint and the hip joint with the classic total hip replacement and with the surface replacement, in carrying out the stress-strain analyses, and in mutually confronting the results obtained. The problem has been solved as a direct task by means of computational modelling, by the method of finite elements in the ANSYS. The computational model consists of these components: sacral, pelvic and femoral bone, muscles, cup, and femoral compponent. and Obsahuje seznam literatury