Abstract. The paper presents the numerical analysis of stress occurring in the most wearable parts of knee joint endoprostheses. That applies to the pair: sled -spherical insert. The Finite Elements Method makes it possible to calculate the stress in particular elements of the tested model. The interaction between the two parts of endoprosthesis takes place on a comparatively small contact surface. Keywords: contact stress, FEM, endoprosthesisThe Finite Elements Method (FEM) makes it possible to conduct a wide range of numerical analyses of strength with the usage of virtual models. As the method provides much more precise results than any simplified analytic calculations, it is commonly used in engineering calculations. Additionally, it is cheaper and easier in application than other experimental methods and furthermore faster in obtaining the results, which is critical in any real conditions. With FEM it is possible to define the values of stress in friction nodes of knee joint endoprostheses, regardless of the shape of sleds or polyethylene inserts, subjected to different loads. Therefore the stress and strain values distribution is clear and obtained quickly, even if there are many similar models of endoprostheses considered, without the necessity to bear the costs of constructing each of them separately; furthermore, it can quickly optimize construction. Polyethylene inserts applied in knee joint endoprosthesesProperly adjusted joints' elements, like sleds and polyethylene inserts, can significantly reduce the problem of high contact stress in the area where the components are subjected to friction and wear. As polyethylene has lower strength values than titanium alloy, the shape of the inserts must ensure the reduction of wear. However, the perfect shape is still being sought and worked on, as the geometry of polyethylene insert must be optimal in order to prolong the time between implantation and the next surgery.

AbstractThe aim of the study was to present numerical strength analysis of the virtual knee and hip joints for the most popular tribological pairs used in prosthetic arthroplasty based on the Finite Elements Method. FEM makes it possible to calculate the stress in particular elements of the tested models. The research was dedicated to elucidate abrasive wear mechanisms during surface grinding of a polyethylene UHMW and a metal elements of endoprostheses. Strong adhesion was found between the abrasives and workpieces, which might be attributed to the chemical bonding between the abrasives and workpieces in synovial liquid. Therefore, the wear of UHMWPE is both chemical and physical. Abrasive wear effect, as a result of the abrasive wear process, is associated with material loss of the element surface layer due to the separation of particles by fissuring, stretching, or micro-cutting.

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The paper presents the numerical analysis of stress and strain occurring in the most wearable parts of hip and knee joints endoprostheses. The complexity of the processes taking place in both, natural and artificial joints, makes it necessary to conduct the analysis on the 3D model based on already existing mathematical models. Most of the mechanical failures in alloplasty are caused by material fatigue. To cut down the risk of it, we can either increase the fatigue resistance of the material or decrease the load strain. It is extremelly important to indicate the areas where damage or premature wear may occur. The Finite Elements Method makes it possible to calculate the stress and strain in particular elements of the tested models. All presented numerical calculations define quality conclusions concerning the influence of some parameters of endoprostheses on the values of stress and strain that are formed in polyethylene parts of endoprotheses of hip and knee joints. The obtained results help to reveal “weak points” in examined models and thus, counteract the subsequent effects resulting from premature wear of endoprosthesis elements. The numerical analysis was performed basing on the finite elements method using Autodesk Simulation Mechanical 2017 software and the ADINA 7.5.1.

Abstract. The paper presents the numerical analysis of stress occurring in the friction node of bi-condylar knee endoprostheses. The Finite Elements Method allows one to calculate and present the stress distribution in all elements of the computing model.