The design of knee prostheses can be improved by computer aided design and structural analysis based on the finite element simulation. Our assumption is that by knowing the stress patterns between the knee prosthesis components and between this implant and its surroundings, we can better evaluate the wear performances and improve its design. The geometry of mobile bearing knee prosthesis with a polyethylene insert was used to predict peak and average contact pressures in several explicit dynamics finite elements analyses. The contact pressure, shear stress distribution and shear movements at the interface implant-cement and bone-cement are important for prostheses life and were computed. Rigid body dynamics analysis was used to predict body positions and orientations. Numerical modeling and simulations are used to predict contact pressures between three-dimensional surfaces. Our computational results showed a positive matching with experimental data from literature. This modeling approach is sufficiently fast and accurate to be used in design sensitivity and optimization studies of knee implant mechanics.