Fig. 4

The angle between the mechanical axis of the femur and the mechanical axis of the tibia (red lines) was determined as hip-knee-ankle angle (HKA), and measured in this case 172° preoperatively (a), and 179° postoperatively (b). To determine the zone of the mechanical axis, the tibial plate was divided into three equal zones (lateral = L, central = C, medial = M) and the mechanical axis (red line) that passes the tibial plate was defined according to which zone is crossed. In this case, medial preoperatively (c) and central postoperatively (d)