Both sprained ankles and broken ankles are painful and result from similar injuries. An ankle sprain is an injury to the ligaments that join bones to each other; it can be mild, with just stretching of these structures, or severe, with a complete tear of the ligament. Telling a sprained ankle from a broken one is not always easy, but some time-tested medical guidelines can help your doctor know whether an x-ray is needed.
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How Ankle Sprains and Fractures Occur
Ankle sprains and broken ankles both occur when the ankle is stressed at an angle. This occurs when you step and land on the inside or outside of the foot. The most common injury occurs when you land on the outside of the foot, stretching the ligaments of the outside of the ankle and sometimes causing the fibula, the small bone on the outside of the leg, to break. This break is almost always at the bottom end of the fibula. Because the type of injury that causes a break and a strain is the same, it can be difficult to know whether the ankle is broken. The ankle is a complex joint, including the two bones of the lower leg, the tibia and fibula, and the bones of the back and middle of the foot, the talus and the calcaneus. In the middle of the foot are the navicular and cuboid bone, and just in front of these sit the three cuneiform bones. Numerous ligaments and tendons of the ankle can be sprained with abnormal twisting or rolling of the ankle.
When It Is Most Likely a Sprain
If you can put weight on the ankle just after the injury and several hours later, and you don't experience too much pain when certain areas -- the lower tips of the inner and outer ankle bones, and over the top and sides of the foot just in front of the ankle bones -- are pressed, the injury most likely is a sprain. With a mild ankle sprain, you're likely to have mild or no swelling, tenderness to the touch but no severe pain, and you'll be able to walk.
When It Is Mostly Likely a Fracture
If you are unable to walk just after the injury or when you see the doctor later that day, an x-ray is needed so the doctor can look for a fracture. It is also more likely to be a fracture if there is pain just over the inside or outside ankle bones or over the top or sides of the foot, just in front of the ankle joint. If swelling and pain don't resolve after a day or two with rest, ice, compression with an elastic bandage and elevation, a doctor should do an evaluation for a broken ankle. Instability of the foot or ankle, deformity or a bone piercing the skin requires immediate medical evaluation, and you may need a ride to the emergency room.
The Ottawa Ankle Rules
The "Ottawa ankle rules" are guidelines that health-care providers can use to evaluate an ankle injury. If you are under age 18 or impaired by drugs or alcohol, distracted by pain from other injuries, have abnormal sensation in the legs and too much swelling for the doctor to properly feel the inside ankle bone, an x-ray is typically needed to exclude the possibility of a fracture.