Use of the Finite Element Method in the analysis of load of polyethylene inserts of knee joint endoprosthesis

Abstract

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.

Stress occurring in the friction node of elements in the total knee endoprosthesis

“…All the calculations proved that the stresses in endoprosthesis are concentrated right underneath the contact surfaces of both elements, particularly underneath surface [6]. Figures 8 and 9 present exemplary results of numerical calculations.…”

“…All the calculations proved that the stress underneath the contact surfaces of both elements, particularly surface [6]. Figures 8 and 9 present exemplary results of numerical The most significant is the thickness of the insert = G: G1 = 8 mm, G2 = 13 mm, G3 = 22 mm calculations have been conducted for 9 computing variants, using 3 thick nesses of polyethylene inserts cooperating with 3 different sleds.…”

Numerical analysis of stress distribution generated in polyethylene inserts by knee joint endoprotheses' sleds made of different titanium alloys

“…Poisson's coefficient ν The calculations prove that stress in endoprosthesis is concentrated in the polyethylene insert, right underneath the contact area of both elements, and highest stress is located right underneath the insert's surface [7]. Some examples of the calculations are present in Figures 5-7.…”

Modelado de superficie del polietileno de ultra alto peso molecular (UHMWPE) para reducción del desgaste en la aplicación de prótesis de rodilla

“…En el 2014 Marcin Nabrdalik presento un artículo de análisis numérico sobre los esfuerzos en las zonas más desgastada en la parte de la articulación de la rodilla, trabajó con la modificación geométrica del inserto tibial sugiriendo un inserto de contornos más suavizados y curveados en comparación con el inserto comercial el cual es completamente plano [3].…”

“…Obteniendo resultados muy cercanos con los tres criterios, demostrando que el método desarrollado es una herramienta muy útil para la aplicación del análisis de clasificación más precisa del diseño, permitiendo reducir el uso de costosos estudios experimentales utilizando simuladores fiscos [2] En el 2014 Marcin Nabrdalik presentó un artículo de análisis numérico sobre los esfuerzos en las zonas más desgastada en la parte de la articulación de la rodilla, trabajo con la modificación geométrica del inserto tibial sugiriendo un inserto de forma esférica. [3].…”