Fig. 5

Rotation of the cylindrical femoral axis with respect to the tibial plateau, comparing the 4 different implant types to the native knee. In the native knee, the characteristic external rotation of the femoral axis on the tibia can be observed from extension to flexion. This external rotation can also be noted in the cruciate ligament retaining (GCR) and posterior stabilized (GPS) knee and to an even lesser extent in the rotating hinge knee (RSL). No such external rotation was seen in the total hinge knee (SSL)