Definition. A sprained ankle is an injury that occurs when you roll, twist or turn your ankle in an awkward way. This can stretch or tear the tough bands of tissue (ligaments) that help hold your ankle bones together. Ligaments help stabilize joints, preventing excessive movement. A sprained ankle occurs when the ligaments are forced beyond their normal range of motion. Most sprained ankles involve injuries to the ligaments on the outer side of the ankle. Treatment for a sprained ankle depends on the severity of the injury.