Influence of flexion of the knee and femoral rotation on retropatellar contact in humans

The aim of the present study was to evaluate retropatellar contact characte ristics at different angles of flexion of the knee joint. To this end, 6 ca daveric legs were examined using pressure sensitive film (Fuji Prescale typ e "super low") at angles of flexion of 45 degrees, 60 degrees, 90 degrees a nd 120 degrees both in neutral rotation and 10 degrees internal and externa l rotation of the femur in the same knee joints. A Force of 140 N was appli ed to both the vastus medialis and lateralis, and a comparison made with a medially and a laterally dominating muscle force. The contact areas decreas ed with increasing angles of flexion. The medially dominating muscle tracti on increased the contact area. Comparison between internal and external rot ation revealed a decrease in contact area on internal rotation. The pressur e measurements were comparable in all loading situations. Comparison betwee n neutral and medial traction revealed significant differences in contact a rea, pressure and force. The influence of femoral rotation showed no signif icant difference. A comparison of the different angles of flexion revealed only few significant differences. To prevent the development of retropatell ar arthrosis, maximum contact areas are necessary. The study has shown an a dvantage for medially dominating muscle traction, and external rotation of the femur.