About 10 million sports injuries occur annually. A great many of these are injuries to runners; one of the most common injuries is stress fractures of the foot.

A stress fracture is a small crack in the bone that develops from chronic, repetitive impact from the foot hitting the ground. They occur when the normally microscopic wear and tear of applied stresses -- like running -- are not given time to heal, deepening and widening the small crack.

The bones of the forefoot (metatarsals) are especially prone to these fractures. The bones leading to the big and little toes are slightly more resistant to injury for various reasons. These bones account for 55 percent of the stress fractures in the foot. Other common areas for stress fractures include the bones of the lower leg, the tibia and fibula, where the stress fracture can often be confused with shin splints, irritation of the soft tissues.

The primary symptom of a stress fracture is pain in the front part of the foot that usually comes on during a workout and disappears once you stop exercising. During the first two weeks of symptoms, the pain may be generalized, mild and achy. If the bone is not given time to heal, however, the pain typically becomes focused over the fracture. Eventually, the fracture can extend all the way through the bone and cause a completed break. The pain may become severe enough that it continues once your workout is over and eventually makes running impossible.

Some stress fractures will show on an X-ray as a black line going through the bone. However, even when a complete break has occurred, the injury may not show up on an X-ray if the bones are still aligned. In this case, additional special diagnostic tools may be necessary. An MRI may show the fracture or the increased fluid in or near the fracture. The orthopedist may also request a bone scan, in which radioactive material is injected into the body. The bone scan tracks where these materials gather, typically in the area of healing bone indicating a fracture.

Treatment for stress fractures usually requires decreasing or stopping training until the pain is gone and an exam reveals that the fracture has healed. A splint or brace may be used. If the fracture doesn’t fully heal in a reasonable amount of time -- which varies depending on the location of the injury -- surgery may be necessary. Recovery typically takes between four to six weeks for the bones of the forefoot.

Athletes can return to activity gradually, usually wearing a brace or orthotics in their shoes. Modified activities and strengthening exercises may be recommended to prevent reoccurrence.

Stress fractures can be prevented by increasing the training regimen gradually. Wearing the type of shoes designed for your sport will also help to dissipate body weight evenly and provide cushion to protect the foot. Many sports surfaces are also designed to minimize the impact of play on the body, as in basketball and track.

If you suspect you may have a stress fracture, discuss the problem with your physician. For a listing of primary care physicians or to find an orthopedist, go to Find A Physician .