Ankle joint: The ankle joint is complex. It is made up of two joints: the true ankle joint and the subtalar joint:

• The true ankle joint is composed of 3 bones: the tibia which forms the medial (inside) portion of the ankle; the fibula which forms the lateral (outside) portion of the ankle; and the talus underneath. The true ankle joint is responsible for the up-and-down motion of the foot.
• The subtalar joint is under the true ankle joint and consists of the talus on top and calcaneus on the bottom. The subtalar joint is responsible for the side-to-side motion of the foot.

The ends of the bones in the joints of the ankle are covered by cartilage. The major ligaments of the ankle are: the anterior tibiofibular ligament (connecting the tibia to the fibula), the lateral collateral ligaments (attaching the fibula to the calcaneus to give the outside of the ankle stability), and the deltoid ligaments on the inside of the ankle (connecting the tibia to the talus and calcaneus and providing medial stability to the ankle).

In medicine, the ankle is the meeting of the leg and the foot; it is strictly the articulation of the tibia, fibula, and the talus. In popular usage, the ankle is often taken to be the ankle joint proper plus the surrounding region including the lower end of the leg and the tarsus, the start of the flat of the foot.