The ankle is comprised of three bones, one of which (the talus) sets inside a cavity formed by the other two (the tibia and the fibula). Each one is joined to the other by a short ligament. Any of these ligaments may be torn (sprained) or the bones may break (fracture) where the ligaments attach. This usually occurs in response to a twisting injury.
Most sprains and some fractures may be treated by immobilization alone (i.e., casts, splints or fracture boots), but some may require surgical intervention. When a fracture (break) occurs along a joint surface, the corresponding pieces must heal in a nearly anatomic position to lessen the chances of developing a traumatic arthritis.