An ankle sprain is a very common injury — approximately 25,000 people experience it each day. Ankle sprains happen when the foot twists, rolls or turns beyond its normal motions. When an ankle is sprained, the foot is typically planted unevenly on a surface, beyond the normal force of stepping. This causes the ligaments to stretch beyond their normal range in an abnormal position.
If there is a severe ankle roll, the forces cause the ligaments to stretch beyond their normal length. If the force is too strong, the ligaments can tear. You may lose your balance when your foot is placed unevenly on the ground. You may fall and be unable to stand on that foot. If enough excessive force is applied to the ankle, you may even hear a "pop" sound. Pain and swelling will result after the injury.
The injured ligament may feel tender. If there is no broken bone, the doctor may be able to tell you the grade of your ankle sprain based upon the amount of swelling, pain and bruising. The doctor may need to move your ankle in various ways to see which ligament has been hurt or torn. If there is a complete tear of the ligaments, the ankle may become unstable after the initial injury phase passes. If this occurs, it is possible that the injury may also cause damage to the ankle joint surface itself. The doctor may order an MRI (magnetic resonance imaging) scan if he or she suspects a very severe injury to the ligaments, injury to the joint surface, a small bone chip or other problem. The MRI can make sure the diagnosis is correct. The MRI may be ordered after the period of swelling and bruising resolves.
Walking may be difficult because of the swelling and pain. You may need to use crutches if walking causes pain. Usually swelling and pain will last two days to three days. Depending upon the grade of injury, the doctor may tell you to use removable plastic devices such as castboots or air splints. Most ankle sprains need only a period of protection to heal. The healing process takes about four weeks to six weeks. The doctor may tell you to incorporate motion early in the healing process to prevent stiffness. Motion may also aid in being able to sense position, location, orientation and movement of the ankle (proprioception). Even a complete ligament tear can heal without surgical repair if it is immobilized appropriately. Even if an ankle has a chronic tear, it can still be highly functional because overlying tendons help with stability and motion.
Reviewed by health care specialists at UCSF Medical Center.