Fig. 6

Projections of the cylindrical femur axes onto the tibial plateau for the different implants in 20° (A) and 85° (B) of flexion. In 85° of flexion, the externally rotated and posteriorized position of the femoral axis can be seen in the native knee. The axis position of the cruciate ligament retaining (GCR) and posterior stabilized (GPS) primary knees approximate this position without, however, being able to fully imitate the external rotation and femoral rollback of the native knee. The axes of the rotating hinge knee (RSL) and the total hinge knee (SSL) are located more ventrally in both positions without showing any relevant movement from extension to flexion