Fig. 5.

The illustration of tibial coordinate system.

In the custom coordinate system of the tibia, the most concave point on the medial tibial plateau, the most concave point on the lateral tibial plateau, and the center point of the ankle joint were selected to construct coronal plane C′ of the custom coordinate system. The center of the tibial knee joint and the center of the ankle joint connect to form a mechanical axis of the tibia. The sagittal plane is plane S′ perpendicular to the coronal plane through the mechanical axis, and the plane pairwise perpendicular to the coronal plane and the sagittal plane is transverse plane A’. Tibial coordinate system, Z: the line connecting the center point of the tibia knee joint and the center point of the ankle joint, point to proximal. Y: the line perpendicular to the coronal plane C′, point to anterior. X: the line perpendicular to both Z and Y, point to lateral.