Figure 1.

Two-dimensional four-bar linkage model of the ankle joint to describe dorsi/plantar flexion in unloaded conditions. The talus/ calcaneus complex and tibia/fibula complex rotate about each other on approximately inextensible line segments, represented by the calcaneofibular (AC) and tibiocalcaneal (BD) ligaments. The other two bars in this four-bar linkage model are formed by: 1) the bony segment connecting the proximal insertions of calcaneofibular and tibiocalcaneal ligaments (AB, red dashed line); and 2) the bony segment connecting the distal insertions of calcaneofibular and tibiocalcaneal ligaments (CD, red dashed line). Redrawn from Leardini etal. J Biomech. 1999 Jun;32(6):585-91.