Ankle 

The ankle is a complex mechanism. It is made up of two joints: the subtalar joint, and the ankle joint.

The ankle joint is composed of 3 bones : the tibia which forms the inside, or medial, portion of the ankle; the fibula which forms the lateral, or outside portion of the ankle; and the talus underneath. The ankle joint is responsible for up (dorsiflexion) and down (plantar flexion) motion of the foot.
Below the ankle joint is the second part of the ankle, the subtalar joint, which consists of the talus on top and calcaneus on the bottom. The subtalar joint allows side to side motion of the foot.

The ends of the bones in these joints are covered by articular cartilage. The major ligaments of the ankle are: the anterior tibiofibular ligament which connects the tibia to the fibula.

The lateral collateral ligaments (anterion, medial and posterior), which attach the fibula to the calcaneus and gives the ankle lateral stability; and, on the medial side of the ankle, the large and strong deltoid ligament, which connect the tibia to the talus and calcaneus and provide medial stability.

These components of your ankle, along with the muscles and tendons of your lower leg, work together to handle the stress your ankle receives as you walk, run, jump and pivot to change direction.

The ankles support the entire weight of the body and are particularly susceptible to injury.

An ankle injury usually involves a sudden, unexpected, loss of balance, resulting in a sharp twist of the ankle. A strain occurs when a muscle or tendon becomes overstretched. A sprain is more serious and occurs when ligaments (the strong connective tissue that connects one bone to another) become overstretched.