Fig. 3

Boundary conditions. A Neutral position of the ankle joint (Initial position): An radius around the y-axis at the reference point-1 (RP-1) of the talus was applied under the compression force from the tibia and fibula (the red arrow marked “a”). B Hyperplantar flexion of the ankle joint: Impingement of the posterior process of the talus against the posterior malleolus (the red arrow marked “b”)