Mobile-bearing type knee prosthesis has been used in total knee arthroplasty (TKA) to improve the mobility of the knee joint. In this type of knee prosthesis, UHMWPE tibial insert is not fixed to the tibial component and able to move freely on the top surface of tibial component. Although deep flexional motion can be expected using the mobile-bearing prosthesis, the safety of the prosthesis, especially the stress state of the tibial insert has not been clarified yet. The purpose of this study was to understand the stress variation in the tibial insert under deep knee flexional motion using the dynamic finite element analysis. It was found that if the movement of the mobile-bearing system is firmly restrained during flexional motion, the stress level tends to increase up to 90 MPa, while the maximum stress level is settled down at 55 MPa when the system works very smoothly.
