Stress fractures were first described in sports medicine in 1958. Since then, their prevalence has only increased, especially in athletes and military recruits. The prevalence of stress fractures is especially high in athletes and military recruits, with 10 to 31% of stress fractures occurring in running sports. A stress fracture is the result of an accumulation of micro-damage from repetitive loading of a bone, leading to fatigue within the bone, causing a crack.

The crack does not traverse the entire bone compared to a frank fracture from trauma, which separates the two ends of the bone. A stress fracture is considered an overuse injury and can arise in any bone. However, 95% occur in the lower limb, with the tibia being the most common.

What causes a Stress Fracture?

The direct cause is not fully understood. It's been suggested that stress fractures represent a failure of functional adaptation.

What are the Risk Factors?

• Intrinsic factors include age, gender, race, poor fitness level, and decreased muscular strength
• Extrinsic factors include an intense training regimen, improper footwear, hard training surfaces, and the type of sport being performed
• Biomechanical factors are low bone mineral density and bone geometry
• Anatomic factors include foot shape, leg length discrepancy, and knee alignment
• Hormonal factors include delayed menarche, menstrual disturbances, menopause and contraception
• Nutritional factors include low calcium and vitamin D in the diet, and eating disorders

Training regimen seems to be the most influential risk factor. For example, an improper increase in running mileage, abrupt or rapid changes in duration, frequency or intensity of training all lead to an increased risk of stress fractures. This mainly occurs due a lack of adequate rest to allow the bone to respond to the new stimulus and strengthen itself via remodeling.

What are the Symptoms?

People with stress fractures describe a sudden onset of pain over the affected region without having experienced any form of previous trauma. Initially the pain will occur during the provoking activity, with relief coming by rest. With continual activity at the same level, the pain will be felt after the activity and will later cause the athlete to cease the sport. Eventually the patient will experience pain at rest. Imaging studies, such as x-rays, bone scans, CT scans or an MRI may be necessary to diagnosis a stress fracture.

What is the treatment, and can stress fractures be prevented?

If a stress fracture is diagnosed, the patient must eliminate the provoking activity and rest. In some cases, immobilization (e.g., a cast, protective orthotic braces), bed rest or crutches are prescribed. Some stress fractures may require surgery, depending on the location and severity. An alternative training program may be implemented to maintain fitness, such as water running or swimming during the period of rest. Alternative training programs should be confirmed with the patient's medical practitioner.

Once the patient achieves two to three weeks of pain-free, full-weight bearing activity, he or she may gradually resume their sport. As a rule of thumb, activity should not be increased by more than 10% per week. If there is recurrence of pain, the patient must be placed on a two-week program of modified activity, until the pain is resolved.

There are many ways to help prevent stress fractures. It's important to maintain your muscular strength, and always allow for adequate rest between sports or training intervals. It's also important to eat a healthy balanced diet. And if you're implementing changes to your training regimen - whether it's the intensity, type of training or the materials used in your training - make sure you introduce these changes gradually to minimize the risk of stress fractures or other training-related injuries.