The fibula is one of the two bones that make up the lower leg, and is the thinner of the two (the other bone is the tibia). Because your lower leg can bear quite a bit of weight and strain during sports that require running and jumping, these bones are prone to stress fractures, or tiny cracks in the bone. Although the fibula is the site of a stress fracture less often than is the tibia (because the tibia, being larger, takes on more of the weight and strain), the fibula can develop a stress fracture.
Athletes whose feet overpronate (rotate inward and downward) have a higher risk of a stress fracture of the fibula. That’s because overpronation means some of the muscles in the lower leg must work harder while running. Symptoms of a stress fracture of the fibula commonly include pain and tenderness, especially when you place weight on the leg or when you press on the bone with your finger.
If you think you have a stress fracture of the fibula, you should stop training and rest the leg. Stretching the muscles of the leg can facilitate healing, as can wearing a brace for support. It’s very important to make sure you are free from pain before you resume activity, since failure to allow the fibula to heal properly can cause the injury and pain to linger for months.
To prevent a stress fracture of the fibula, make sure you increase mileage and training gradually, and that you wear equipment and footwear that properly support your feet and legs, if applicable.