COMPARATIVE EXAMINATIONS OF THE RIGIDITY, DEFORMATION AND ABSORPTION BEHAVIOR OF DIFFERENT ARTIFICIAL HIP JOINTS UNDER DYNAMIC LOADS

The biomechanical reasons for moving and loosening of the acetabular c up and femoral prosthesis are still unclarified. Especially, chronic a nd mechanical overloads of the inferfaces, which are caused by the cha nge 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 publicatio n aims to complete the knowledge about mechanical properties of artifi cial hip joints. Primarily, we focused on the quantitative registratio n 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. Conve ntional test methods work according to the principle of constancy of m aximum forces and excitation frequencies. They do not consider the for ces of inertia resulting from body mass, even though these reaction fo rces are decisive for the dynamic properties and mechanical behaviour of the components of endoprotheses. A selection of representative impl ants from several manufacturers were tested according to the new test method, which is based on the ''mass- spring, absorber'' principle. Th e examined prostheses regarding differed in material, method of fixati on and geometric dimensions. The results of these examinations give cl ues to the repercussions of the mentioned parameters on the dynamic be haviour of endoprosthetic systems. In order to evaluate the results, h ip joints from animals were also examined and provided relevant inform ation for desirable alternative solutions to the problem in view of co nstruction and material.