Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Ankle Sprain

What Is It?

An ankle sprain is a stretch or tear in one or more of the ankle ligaments. Ankle ligaments are slightly elastic bands of tissue that keep the ankle bones in place. Ankles are particularly prone to sprain because of the small size of the joint and the forces exerted when walking, running and jumping, especially if the surface is uneven.

Depending on the severity of the injury, an ankle sprain is classified as:

• Grade I — The ankle is painful, but there is little ligament damage and little loss of function.

• Grade II — There is moderate ligament damage, and the ankle joint is somewhat loose.

• Grade III — One or more ligaments are torn, and the ankle joint is very loose or unstable.

Millions of ankle injuries occur each year in the United States. Most of them are sprains. Most sprains happen when the ankle twists suddenly. The most common injuries happen when the foot rolls onto the outside of the ankle, straining the outside ligaments of the ankle joint. These are called inversion injuries. Less common are eversion injuries, which happen when the ankle rolls onto the inside of the joint, stretching the ligaments on the inner side of the ankle.