An ankle sprain is an injury to one or more ligaments in the ankle, usually on the outside of the ankle. Ligaments are bands of tissue—like rubber bands—that connect one bone to another and bind the joints together. In the ankle joint, ligaments provide stability by limiting side-to-side movement.
Some ankle sprains are much worse than others. The severity of an ankle sprain depends on whether the ligament is stretched, partially torn or completely torn, as well as on the number of ligaments involved. Ankle sprains are not the same as strains, which affect muscles rather than ligaments.
A sprained ankle is often caused by rolling the ankle during sports, hiking or other physical activity.