Evaluation of the Malalignment Varus - Valgus in Total Knee Arthroplasty Designed for Deep Knee Flexion Using Knee Kinematic Motion Simulator

Abstract

Revision total knee arthroplasties cause performed aseptic loosening, instability, and polyethylene wear. 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 applied at a 90° knee flexion. Elevation of the lateral condyle due to valgus malalignment will distribute more contact force on the medial 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 valgus 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 90° to 150° knee flexion and increased with increasing knee flexion. Maximum gap occurs at 5° malalignment in the amount of 5 mm at 150° of knee flexion. The aim of this study was therefore to evaluation malalignment valgus 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 an narrow down gap between femoral and polyethylene component used knee kinematic motion simulator, this accommodate deep knee flexion movement in daily activities and reduce the possibility of subluxation and dislocation at the polyethylene component during deep knee flexion. A wide gap between the femoral component and the polyethylene component and a significant amount of contact force in the medial condyle region might be the explanation for polyethylene component damage. It is expected that potential medial or lateral condylar lift at some stage during the gait cycle can be reduced.