I saw a young athlete last week complaining of shin pain. The source of the pain was a stress fracture. It is estimated that between five and 30 percent of athletes and military recruits develop a stress fracture each year. Briefhaupt was the first person to describe the condition in military recruits in 1855.

Everyone is familiar with bone fractures, especially those that result from acute trauma. These fractures are usually easy for an untrained person to see on an X-ray - the bone looks like a broken stick. Stress fractures, however, can be much more difficult to diagnose.

Stress fractures result from repeated stress on a particular part of a bone. This repetitive microtrauma causes disruption of the microscopic structure of the bone over time that eventually exceeds the bone's ability to heal itself. A tiny crack develops in the bone that may or may not be obvious on an X-ray. Think of bending a piece of metal over and over. Eventually it weakens and cracks or breaks.

Stress fractures typically occur in bones that are prone to repetitive stress based on particular sports. Stress fractures can involve any bone, but the most common fracture locations and their associated sports include the leg and foot (runners, jumpers), the spine (gymnasts, divers & volleyball players), arms (throwers), and ribs (rowers). The forces experienced by bones in the feet and legs can be up to twelve times a person's weight. Stress fractures are one of the five most common injuries in runners and account for up to half of injuries in military recruits.

Risk factors for stress fractures can be divided into intrinsic, originating within the body, and extrinsic, coming from outside the body. Intrinsic factors can include gender (twice as likely in females), weak or imbalanced muscles, prolonged rest that can lead to weak bones, leg misalignment, being tall and having poor foot structure.

One very important intrinsic risk factor is osteoporosis. This is especially worrisome in young female athletes and can be part of the "female athlete triad." This triad includes disordered eating (anorexia, bulimia, etc.), amenorrhea (no menstrual periods) and osteoporosis. Any young woman who has a stress fracture needs to be evaluated for the female athlete triad.

Extrinsic risk factors usually include excess quantity or intensity of training, a poor training surface (too hard or too irregular), and worn out or improperly fitted shoes. Running shoes should be fitted correctly to the foot structure, preferably at a professional running shoe store, and should not be used over 300 miles or so. Other extrinsic factors include smoking, poor nutrition, and medications (especially oral steroids).

A person with a stress fracture usually presents with a particular history. The pain typically comes on gradually and initially is felt at the end of the activity that causes the pain. The pain then becomes more severe causing the person to limit participation. Early on, the pain is relieved with rest while it may not be as the injury progresses. Many patients complain of pain at night, and athletes frequently have a hard time pinpointing a specific spot where it hurts.

The physical exam often offers clues to the diagnosis. Pain is usually elicited when pressing or tapping the affected area. There may be swelling or redness at the site as well. Having the patient put stress on the bone by hopping, etc. may worsen the pain.

If the diagnosis is not obvious using the history and physical exam, other tests may be needed. Conventional X-rays often are normal. Often CT or MRI scanning is needed to locate the fracture. Nuclear bone scans can also be useful. What study to order is usually determined by the site of the possible fracture and other medical conditions the patient may have.

Treatment is fairly simple - break the cycle of repetitive stress on the bone. This is done by cross training to strengthen the muscles around the fracture site without putting stress on the bone. Rehabilitation usually takes four to 12 weeks depending on the site and severity of the fracture. Occasionally stress fractures do not heal and require surgical stabilization. One rule of thumb is to increase activity about ten percent a week during rehabilitation. As far as treating the pain, there is some evidence in animal models that taking Non-steroidal medications such as Aleve and ibuprofen for pain can delay healing.