A stress fracture is a fatigue-induced bone fracture caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated injury from repeated submaximal loading, such as running or jumping. Because of this mechanism, stress fractures are common overuse injuries in athletes. Stress fractures can be described as small cracks in the bone, or hairline fractures. Stress fractures of the foot are sometimes called "march fractures" because of the injury's prevalence among heavily marching soldiers. Stress fractures most frequently occur in weight-bearing bones of the lower extremities, such as the tibia and fibula (bones of the lower leg), metatarsal and navicular bones (bones of the foot). Less common are stress fractures to the femur, pelvis, and sacrum. Treatment usually consists of rest followed by a gradual return to exercise over a period of months. Signs and symptoms Stress fractures are typically discovered after a rapid increase in exercise. Symptoms usually have a gradual onset, with complaints that include isolated pain along the shaft of the bone and during activity, decreased muscular strength and cramping. In cases of fibular stress fractures, pain occurs proximal to the lateral malleolus, that increases with activity and subsides with rest. If pain is constantly present it may indicate a more serious bone injury. There is usually an area of localized tenderness on or near the bone and generalized swelling in the area. Pressure applied to the bone may reproduce symptoms and reveal crepitus in well-developed stress fractures. Anterior tibial stress fractures elicit focal tenderness on the anterior tibial crest, while posterior medial stress fractures can be tender at the posterior tibial border. Causes Bones are constantly attempting to remodel and repair themselves, especially during a sport where extraordinary stress is applied to the bone. Over time, if enough stress is placed on the bone that it exhausts the capacity of the bone to remodel, a weakened site—a stress fracture—may appear on the bone. The fracture does not appear suddenly. It occurs from repeated traumas, none of which is sufficient to cause a sudden break, but which, when added together, overwhelm the osteoblasts that remodel the bone. Potential causes include overload caused by muscle contraction, amenorrhea, an altered stress distribution in the bone accompanying muscle fatigue, a change in ground reaction force (concrete to grass) or the performance of a rhythmically repetitive stress that leads up to