Influence of the fixation region of a pressfit hip endoprosthesis on the stressstrain state of the boneimplant system

Although significant progress has been made in the development of total hip replacement, behaviour of the femoral component of an endoprosthesis in relation to the type of its fixation in the bone is still not fully understood. In this paper, behaviour of the femoral bone and the stem prosthesis is studied taking into account different types of prosthesis fixation in the medullary canal of the femur under the action of functional loads. For an analysis, a three-dimensional model of a femur has been developed based on the results of a computed tomography. The stressstrain state governing behaviour of the femoral bone and the stem prosthesis has been estimated with the use of the finite element method (FEM).The FEM analysis has shown that for the diaphyseal fixation, the area of contact between the surface of the endoprosthesis and the bone is insufficient and leads to large stresses in the implant accompanied by stress concentration in the distal femur. An increase in the area of contact between the implant and the bone raises the stiffness of the "boneimplant" system, which, in turn, reduces stresses in the implant. The applied metaphyseal-type fixation yielded an improvement of results regarding behaviour of the femoral bone and the stem prosthesis. Namely, the study yielded the distribution of stress in the bone similar to the physiological stress state. A Fortran subroutine of femur bone adaptation is developed.Influence of the type of prosthesis fixation on the bone remodelling is studied and quantified.The risk of stress shielding effect yielded in the case of the prosthesis with distal fixation is discussed.The differences in peak stresses in the stem prosthesis are detected and numerically evaluated.Possible reduction of stress shielding in the case of proximal fixation of the stem is detected.