3-D finite element model of a typical PS type knee prosthesis was constructed using its CAD data with use of a nonlinear spring model and an analytical load data for deep squatting. Stress analysis was then performed by an explicit finite element method under continuous deep flexion motion. It was shown that the equivalent stress on the Post surface rapidly increases due to the Post/Cam contact. Severe stress concentration is also generated on the surface. This kind of stress concentration may cause damage and failure of the Post. Wear analysis was also performed based on the results of the stress analysis and the classical wear theory. Wear depth was then estimated and the analytical result suggests that the developed FE model is useful for risk assessment of knee prostheses.