Structure Design and Performance Analysis of a Stem for Tumor-type Knee Prosthesis

Background: After undergoing tumor-type knee prosthesis replacement, patients with bone tumor in the distal femur may experience aseptic loosening on the femoral side, potentially resulting in implant failure. Compared with the traditional bone cement fixation method, the biological fixation can ensure the long-term stability of the prosthesis. To reduce stress shielding of the biologically fixed femoral stem and enhance its initial stability, this study focuses on the structural design and performance analysis of porous femoral stem. Method: The three-dimensional model of the knee joint was constructed using inverse modeling, and the finite element models were established for prosthetic replacements featuring various femoral stem lengths and fixation methods. The fretting of the femoral stem was designed based on a triply periodic minimal surface (TPMS) structure. To determine the most suitable TPMS structure, quasi-static compression and friction test were performed. Additionally, gait experiments were conducted to collect patient-specific data, using for the loading of the finite element analysis. Result: Both fixation methods exhibited stress shielding, and it increased with greater stem length. Constraining the top of the femoral stem at the femoral isthmus was found to reduce the fretting of the femoral stem. Experimental results showed that the Gyroid structure with 60% porosity demonstrated higher yield strength and friction coefficient, furthermore it maintained an elastic modulus comparable to that of natural bone tissue. Based on data collected from gait experiment, finite element analysis showed that porous femoral stems can effectively reduce stress shielding and fretting. Conclusion: The new type of femoral stem with porous structure can effectively reduce stress shielding and enhance initial stability, providing a valuable reference for future femoral stem design.