Three-dimensional Finite Element Analysis And Biomechanical Study On Reconstruction Of The Large Defect Of Proximal Femur With Custom Endoprostheses

Objectves: To create three-dimensional finite element models of reconstruction of the large defect of proximal femur with custom endoprostheses and analyse the influence of the custom endoprostheses with different intramedullary stem-lengths on the stress distribution of femur-cement-prosthese.The optimal stem-length of custom endoprostheses is discussed to guide clinical work.Material & Method: Three-dimensional finite element models of reconstruction of the large defect of proximal femur and custom endoprostheses with different stem-lengths(160mm,140mm,120mm,100mm, 80mm)were created using CT-scan and computer aided design(CAD) methods. Loads were established and applied on the endoprosthese to simulate the values for walking. The stress on femur-cement-prostheses and the influence of stress on the different stem-lengths were analysed.Results: The stress on the lateral and medial of the proximal femur increase gradually from the proximal end of the femur to the distal end and reach its highest value at the tip of the prostheses which is under the fatigue strength of the femur shaft.The variations of the stem-length have no significant influence on stress-shielding of the proximal femur,but have influnce on the region of stress-shielding. The stress on cement mantle increase from the proximal end of the cement mantle to the distal end andreach its highest value near the tip of the prostheses.The prostheses with stem-lengths of 120mm, 100mm, 80mm increase the stress on the cement mantle to the value beyond the fatigue strength of the cementBut when the stem-length is 140mm or 160mm, the stress is under the value. The highest stress value on the prosthese stem is near the tip of the stem, which is under the fatigue strength of the stem itself.Conclusion: 1.Decreasing the length of the intramedullary stem can not decrease the level of the stress-shielding on the proximal femur, but it can decrease the region of the stress-shielding to some extent. 2.The intramedullary stem of the custom endoprosthese must be with enough length to decrease the stress on the cement mantel in order to avoid the loosening of the prostheses. 3.For the reconstruction of the 130mm defect of the proximal femur, the optimal length of the intramedullary stem of the custom endoprostheses is 140mm.