Emulating the human tibiofemoral joint by using a four-bar linkage, condylar shapes and slip ratio variation

This study evaluates a biomechanical design concept of the tibiofemoral (TF) joint by using a four-bar linkage (FBL) mechanism on a sagittal plane in order to accurately simulate the motion of the human knee. Also included are the design objectives and parameters of both the endo- and exo-prostheses of the knee, both of which derive from TF characteristics. The exo-prosthesis of the knee depends only on the femoral polode (or the moving polode (MP) linkage). On the other hand, the endo-prosthesis of the knee relies upon the TF condylar surface and the slip ratio variation, without needing to consider the femoral polode. By calculating the polodes of the FBL mechanism and by applying envelope curve applications, the proposed design concept incorporates both the endo- and exo-prosthesis parameters with the multi-objective goal of recreating the full functionality of the TF joint. Those results demonstrate that the slip ratio adjusts to the TF condylar surface even if the femoral polode is unaltered, thereby determining the optimal measurement between the pole and contact point with the TF condylar surface.