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. Although self-care measures and over-the-counter pain medications may be all you need, a medical evaluation might be necessary to reveal how badly you've sprained your ankle and to put you on the path to recovery.
Most ankle sprains involve injuries to the three ligaments on the outside of your ankle. Ligaments are tough bands of tissue that stabilize joints and help prevent excessive movement. An ankle sprain occurs when you roll, twist or turn your ankle in an awkward way. This can stretch or tear the ligaments that help hold your ankle bones together.
Source: http://www.mayoclinic.com