Evaluation varus stress in total knee arthroplasty designed for deep knee flexion using knee kinematic motion simulator

Revision total knee arthroplasties cause performed aseptic loosening, instability, and polyethylene wear. The collaboration between surgeons and engineers for resulted in many developments in prosthesis design is needed. Separation or removal of the femoral component has been observed and this has the potential to severely damage the polyethylene component. In most cases 90% of the patients examined experienced significant medial or lateral condylar lift at some stage during the gait cycle. Using the MRI, a normal knee has maximum lateral lift is approx. 6.7 mm and maximum medial lift is approx. 2.1 mm, when a varus strees was applied at a 90° knee flexion. Elevation of the medial condyle due to varus malalignment will distribute more contact force on the lateral condyle. In this study, a polyethylene component of a posterior-stabilized right knee joint implant was developed to facilitate a high range of motion (ROM). Malalignment varus was observed with the axes of knee motion joint implants were varied from 0, 2, 3 to 5° and knee bend measurements at 30, 60, 90, 120, and 150° of knee flexion. Using the knee kinematic motion simulator, the modified polyethylene component resulted in 0° malalignment there is no gap of the femoral component with the polyethylene component, from 30 to 150° of knee flexion. At 2° malalignment, the femoral component was raised by 0.5 mm at a 120 to 150° knee flexion and increased with increasing knee flexion. Maximum gap occurs at 5° malalignment in the amount of 2 mm at 150° of knee flexion. The aim of this study was therefore to evaluation malalignment varus of the flexed knee using knee kinematic motion simulator, with reference to the tibiofemoral flexion gap. The result that the modified design is expected in a narrow down gap between femoral and polyethylene component to accommodate deep knee flexion movement in daily activities and reduce the possibility of subluxation and dislocation at the polyethylene component during deep knee flexion. Widest gap between femoral component and the polyethylene component more contact force on the lateral condyle increases potential wear or fracture the polyethylene.