Three-dimensional Finite Element Analysis And Biomechanical Study On Reconstruction Of The Large Defect Of Proximal Femur With Allograft Prosthesis Composite

Objectves: By using mathematical mechanics method, Three-dimensional finite element models of the large defect of proximal femur were reconstructed with allograft prosthesis composite in Three bone-healing phases. Then these models were tested under two physical loads. By analysing the stress distribution of femur-cement-callus-prostheses safe physical loads were found in different bone-healing phases. The optimal post-operation scheme is selected to guide clinical work.Material & Method: The femur was constructed with efilm software from CT data, then to create three-dimensional concrete models by using ProeWildfire software, in final three-dimensional finite element models of allograft prosthesis composite were made in ANSYS 11 software. Loads were simulated the peaking values during stance walking and straight leg raising. The stress on femur-cement-callus-prostheses and the influence of stress on the different bone-healing phases were analysed. Results: Among three models the stress distribution of femur almost are identical, the stress on the lateral and medial of the proximal femur are high and reach its highest value at the tip of the Prostheses which is under the fatigue strength of the femur shaft. The highest stress value on the cement mantle is near the tip of the stem Among B and C models, which is under the fatigue strength of the cement itself, but the A model is very different from B and C models, The highest stress value on the cement mantle is near medial side of the sectional plane and is beyond the fatigue strength of the cement. The highest stress value on the Prostheses stem is near the upper 4cm of the stem tip Among B and C models, which is under the fatigue strength of the stem itself, but the A model is very different from B and C models, The highest stress value on the prosthese stem is near medial side of the sectional plane and A2 model is beyond the fatigue strength of the Prostheses. Among three callus models the stress distribution of femur almost are identical, The highest stress value on the callus is medial side of the callus layer and is under the corresponding fatigue strength.Conclusion: 1. Bone-healing strength of allograft and host bone must be acquired so that can transfer stress and prolong lever arm effectively. It may decrease stress in bone cement mantle to prevent fracture of bone sement and loosing of prosthesis. 2. Current model was specified 138mm intramedullary stem-length of host bone and 135mm defect-length of proximal femur, midiumterm callus model and maturing callus model are well enough for stance walking, preliminary callus model are unsuitable for stance walking and should be cautious for straight leg raising.