The general configuration of replaced knee is difficult to anticipate because of the large number of geometrical parameters related to morphology, prosthetic implants and pre-operative choices (such as ligament release). This article features the studies achieved in order to create a decision aiding computer tool dedicated to total knee prosthesis. METHOD AND MODEL: We have built a geometrical modelling of the physiological knee and prosthesis elements association. A numerical processing through biomechanical laws permitted to simulate the geometrical and mechanical behaviour of the whole for different flexing angle.A first validation of the model, comparing the numerical simulation results and the measuring of the 30 implanted knee X-rays, showed a valid matching (86 p.cent of the total cases) between model and real configuration.This tool allows to realise simulations and optimizations with regard to the following issues: decreased risks of the unsealing of the patellar component through contact centering with the trochlea, increased mechanical efficiency of the force transmission from the quadriceps to the tibia, increased maximum flexing angle considering the extension of the quadriceps.The orthopedic surgeon should be greatly assisted in the future preoperative planning by these initial findings.