[Comparative experimental studies on rigidity, deformation and blunting behavior of various total hip endoprostheses...

The biomechanical reasons for moving and loosening of the acetabular cup and femoral prosthesis are still unclarified. Especially, chronic and mechanical overloads of the interfaces, which are caused by the change of stiffness and damping properties of the whole system, cannot be excluded. To date, the description of dynamic behaviour of hip-joint endoprostheses from the viewpoint of material selection and design is insufficient. On the basis of comparative experiments, this publication aims to complete the knowledge about mechanical properties of artificial hip joints. Primarily, we focused on the quantitative registration of certain influences (e.g. design, dimensions and material) on the dynamic properties of different kinds of acetabulum cups. Therefore, a significant new test method was developed for this examination. Conventional test methods work according to the principle of constancy of maximum forces and excitation frequencies. They do not consider the forces of inertia resulting from body mass, even though these reaction forces are decisive for the dynamic properties and mechanical behaviour of the components of endoprostheses. A selection of representative implants from several manufacturers were tested according to the new test method, which is based on the "mass-spring, absorber" principle. The examined prostheses concerned differed in material, method of fixation and geometric dimensions. The results of these examinations give clues to the repercussions of the mentioned parameters on the dynamic behaviour of endoprosthetic systems. In order to evaluate the results, hip joints from animals were also examined and provided relevant information for desirable alternative solutions to the problem in view of construction and material.