Stress Analysis of PS Type Knee Prostheses under Deep Flexion

Abstract

3-D finite element models of two kinds of Stryker's PS type knee prostheses, Scorpio Superflex and NRG, were constructed using their CAD data with use of a nonlinear spring model and an analytical load data for deep squatting. Superflex model was formerly used in TKA, and NRG model is the latest version with a modified design of Post. Stress analysis was then performed by an explicit finite element method under continuous flexion motion from 0 to 135 degree. It was shown that only the condylar surfaces of the femoral component and the tibial insert contacted each other from 0 to 60 degree flexion for both the models, and the stress concentration in NRG was a little higher than that in Superflex. The simulation results also exhibited that severe stress concentration was generated at Post of the tibial UHMWPE insert due to Post/Cam contact. This kind of stress concentration may result in damage and failure of Post. It was shown that the design modification applied to NRG effectively reduced the stress concentration of Post.

Keywords

• total knee arthroplasty
• uhmwpe insert
• deep flexion
• finite element analysis