Three-dimensional Finite Element Stress Analysis For Custom Endoprosthesis In Distal Femur Reconstruction

Objectives: To determine the effects of femoral prosthesis stem length and the percentage of bone removed on stress distribution in the custom endoprosthetic reconstruction system of distal femur.Materials & Methods: CT scans of a 23 years-old man's right femur were obtained. The program ANSYS was used to built eight three-dimensional finite element models. Model A,B,C,D,E represent using different stem-length (150mm, 160mm, 170mm, 180mm, 190mm) custom endoprostheses to reconstruct 40% defect of the distal femur, while Model F, G and H represent using 170mm long stem custom endoprosthesis to reconstruct 30%,40% and 50% defect of the distal femur. The maximum load corresponding to the gait cycle (normal walking) was applied.Results: The stress on the femur decreased gradually from the proximal femur to the distal end. The maximum stress on the bone recorded was in the medial of the proximal femur. The stress on the cement dropped from 27.2Mpa to 19.06Mpa when the stem-length increased from 150mm to 190mm. No bone fracture, cement damage and stem failure occurred in all models except model H, in which the maximum flexural stress on cement exceeded its ultimate strength.Conclusions: Compared to long stems, short stems lead to bone fracture and cement damage more easily. Increasing the length of the intrameduUary stem often increases the level of the stress-shielding on the bone. To reconstruct 40% defect of the distal femur the optimal stem-length is 170mm. When the defect of distal femur is beyond 50%, using custom endoprosthetic to achieve limb salvage might be dangerous.