How to Define the Contact Point of the Tibiofemoral Joint of the Prosthesis in In-Vitro Biomechanical Testing

No standard method has been provided to define the contact point of the tibiofemoral joint of the total knee prosthesis. Our objective was to estimate the contact point of the tibiofemoral joint in in vitro biomechanical testing of the total knee prosthesis. Three commercial knee prostheses were used for testing. We applied compression loads and used Fuji-prescale films to measure the contact areas at different flexion angles (0°, 10°, 30°, and 60°). The contact point was calculated when the maximum contact configuration was achieved. We used a sensitivity analysis and digital image analysis of the Fuji-prescale film to find the contact point at different flexion angles. From the results, we found that the contact points of the 3 prostheses were all approximately at 30%–60% of the depth of the tibial plateau dimension relative to the posterior edge and symmetrically relative to the midline of the mediolaterial width. All three prostheses had the same tendency in which the contact point first moved anteriorly during 0° to 10° flexion, and then moved more posteriorly after 10° flexion. The present method using the maximum contact area to estimate the contact point for different flexion angles, should be applicable for in vitro biomechanical evaluation of the total knee prosthesis.