Stress Analysis of Artificial Knee Joints under Flexion and Rotation

3-D finite element models of two types of PS type knee prostheses were constructed using their CAD data with use of a nonlinear spring model and an analytical load data for deep squatting. PS-type1 model was formerly used in total knee arthroplasty, and PS-type2 model is the latest version with a modified design of post structure. Stress analysis was then performed by an explicit finite element method under continuous flexion motion from 0 to 135 degrees with internal rotation up to 10 degrees. It was shown that the post/cam contact starts at about 65 degrees of flexion, and the equivalent stress rapidly increases due to the contact. Severe stress concentration is also generated on the Post surface due to the post/cam contact. This kind of stress concentration may cause damage and failure of the post. It was clearly shown that the design modification applied to PS-type2 effectively reduced the stress concentration of the post