Sprained and broken ankles are both painful, and they generally occur after similar types of injuries. In an ankle sprain, ligaments that join the bones of your ankle to each other are stretched or torn. In a broken ankle, 1 or more bones of your ankle are fractured. Telling the difference between a sprained and broken ankle can be difficult, especially when a sprain is severe. An x-ray is the best way to know whether your ankle is broken.
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Typically, both ankle sprains and breaks occur when the ankle is stressed at an angle. This happens when your ankle is twisted inward or outward as you land on the outside or inside of your foot. The most common injury occurs when your ankle twists inward, stretching the ligaments on the outside of your ankle and producing a sprain. If the force is strong enough, the ligaments can be fully torn, causing a severe sprain. Sometimes the force is also strong enough to produce a break in the lateral malleolus -- the lower part of the fibula, which forms the bony bump on the outside of your ankle. Less commonly, the ankle twists outward, spraining the ligaments on the inside of the ankle and possibly breaking the medial malleolus -- the lower part of the tibia, which forms the bump on the inside of your ankle. Very severe trauma may produce complicated injuries with torn ligaments and broken bones on both sides of the ankle.
Likely a Sprain
If you can stand -- putting weight on your ankle -- immediately after an injury and several hours later, you likely have a sprain. However, severe sprains with torn ligaments on both sides of the ankle can produce a completely unstable ankle that prohibits all weight bearing. A sprain is also likely if you don't have significant pain when the lateral or medial malleolus is pressed. With a mild ankle sprain, you're likely to have minimal or no swelling, but swelling and bruising can be prominent with moderate and severe sprains. Unless they are severe, ankle sprains should start to improve after a few days with rest, ice, compression with an elastic bandage, and elevation.
Likely a Break
If you're unable to walk immediately after an injury or later that day, a fracture is more likely. Moderate to severe pain when pressing either malleolus is another sign that you likely have a fracture. Swelling and bruising are usually obvious with a fracture. A very deformed ankle or a piece of bone sticking out through the skin indicates the presence of a break. Many fractures require treatment with only a walking cast or boot. Ankle fractures that pierce this skin --- called open fractures -- need urgent surgery to fix the break and close the skin.
Making the Diagnosis
The Ottawa ankle rules, originally described in an article in the September 1995 issue of "The BMJ," are a set of guidelines doctors often use when evaluating ankle injuries. The goal is to identify injuries that are most likely breaks, reducing the use of x-rays for injuries that are probably just sprains. The rules state that x-rays are only necessary for people unable to bear weight on the ankle immediately after the injury and when assessed by the physician, or for people with pain upon pressure along the back of the medial or lateral malleolus. These rules are generally very reliable except when pain cannot be accurately assessed, as when people are impaired with drugs or alcohol, distracted by pain from other injuries or have too much swelling for the doctor to press the correct area.
Seeking Medical Attention
Seek immediate medical attention if your ankle appears deformed, if you have an open fracture or severe pain or if you are unable to walk. If swelling and pain from an injury originally thought to be a sprain are not starting to improve after a few days, see your doctor to check whether you actually have a broken ankle.
Reviewed by Mary D. Daley, MD.