[The geometry of the human trochlea tali].

The geometrical shape of the trochlea tali is responsible for two completely different courses of motion in the ankle joint setting out from the neutral position: dorsiflexion and plantar flexion. Dorsiflexion: The tibia leads the talus, whereas the fibula is pushed laterally by the screw-shaped lateral articular facet of the talus. The malleoli tightly embrace the trochlea tali, whilst an obvious cleft appears dorsally and medially between the superior articular surface of the talus and the tibial roof. Plantar flexion: The fibula leads the talus which withdraws from the medial malleolus by stretching the anterior talofibular ligament. At the same time the superior articular face of the talus closely contacts the tibial roof.