The ankle is the region where the foot and the leg meet. The ankle joint is actually composed by three smaller joints:
- the ankle joint proper, commonly called ankle mortise joint (but also talocrural joint). It is a synovial hinge joint that connects the distal ends of both the tibia and the fibula in the lower limb with the proximal end of the talus.
- the subtalar joint, that occurs at the meeting point of the talus and the calcaneus.
- the inferior tibiofibular joint, between the fibula and the tibia. More precisely, it is formed by the rough, convex surface of the medial side of the distal end of the fibula, and a (corresponding) rough concave surface on the lateral side of the tibia.
The boney architecture of the ankle consists of three bones: the tibia, the fibula (in the leg) and the talus (in the foot). The talus is also called the ankle bone since it’s the most important bone in the ankle articulation. In normal health conditions, the articulation between the tibia and the talus (ankle mortise joint) bears the greatest part of body weight: it is the region where ankle efforts are mostly concentrated.
The medial malleolus is a boney process extending distally off the medial tibia. There is also a lateral malleolus, generated by a distal-most aspect of the fibula. Together, the two malleoli, along with their supporting ligaments, stabilize the talus underneath the tibia.
The ankle joint is bound by the strong deltoid ligament (it is attached at the medial malleolus of the tibia and supports the medial side of the whole joint) and three lateral ligaments: the anterior and posterior talofibular ligaments (they support the lateral side of the joint, from the lateral malleolus to the dorsal and ventral ends of the talus) and the calcaneofibular ligament (it is attached at the lateral malleolus and to the lateral surface of the calcaneus).
The calcaneus is also attached to the Achille’s tendon (also known as the calcaneal tendon or the tendo calcaneus), that is a tendonous extension of gastrocnemius and soleus muscles of the leg. It attaches the heel to the posterior leg.
Concerning the joint motion, the ankle joint theoretically admits 1 degree of freedom: movements of plantar flexion and dorsiflexion.
In addition to these, the geometry of the different bones that form the articulation permits other more limited movements, such as foot eversion and inversion.