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A sprain damages the bands of tissue (known as ligaments) that connect your bones together at the ankle joint. Your sprained ankle might only be mild, or you could have a more serious injury.

Most ankle sprains happen when your foot suddenly twists inwards as you run, turn or fall. You sometimes hear a pop or a tear.

How bad your injury is depends on how much damage you've done to the ligaments around your ankle joint.

There are several ligaments in your ankle. You may have injured one or more of them. Doctors sometimes decide how seriously you've sprained your ankle using these different grades:¹

• Grade 1 is a mild sprain when the ligaments have stretched too far
• Grade 2 is a moderate sprain when the ligaments are partly torn
• Grade 3 is a severe sprain when the ligaments are completely torn.

People who have a high-arched foot or bow legs are more at risk of spraining their ankle. You're also more likely to get a sprained ankle if you've had one before. You can also get an injury known as a strain. This is different to a sprain. A strain happens when you stretch or pull a muscle rather than a ligament.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.