Stress Fractures

Stress fractures are a common sports injury. They are caused by overtraining or overuse. High impact sports, such as gymnastics and basketball, can increase the risk of stress fractures. In these sports, the repetitive stress of the foot striking a hard surface causes cumulative trauma to the bones. Stress fractures usually occur in the weight-bearing bones, such as the bones of the lower leg, the ankle, and the metatarsal bones of the foot.

There are two types of stress fractures. Insufficiency fractures are breaks in abnormal bone under normal force. Fatigue fractures are breaks in normal bone that has been put under extreme force. Fatigue fractures are usually caused by new, strenuous, or repetitive activities such as distance running. These appear as hairline cracks in the bone that can grow larger over time if not treated properly.

What Causes a Stress Fracture?

Placing extreme stress on a bone, over and over again, can cause a stress fracture. Bones normally adapt to repetitive stress, and any change in the function of a bone causes it to change the way it is built. This is how small bumps and ridges form on bones. The tendons pull on these areas, and the bone adapts by building up. This is normal. But repetetive stress can overwhelm the bone's ability to adapt. This is especially true when someone suddenly begins a new, strenuous activity such as running.

Stress fractures are related to both the amount of exercise and how fast people increase their exercise program. The more people run or jump, the more likely they are to develop a stress fracture. Research suggests that most athletes who develop stress fractures have been training for at least two years, six or more times a week. A stress fracture is more likely to occur after an increase in how far, how often, and how hard a person exercises.

Risk Factors

Some people are more at risk for stress fractures than others. Women are up to 10 times more likely to develop stress fractures than men. The reasons for this are unclear. Stress fractures occur less frequently in those of black, African descent than in Caucasians, due to a higher BMD (bone mineral density) in the former. Age also makes stress fractures more likely. This is thought to be due to declining levels of physical activity and age-related reductions in bone mineral density.

Tibial Stress Fractures

A stress fracture in the tibia is a serious problem that at first may have the same symptoms as shin splints. The tibia, sometimes called the shinbone, is the larger of the two bones that support the lower leg. Continual stresses from running on hard surfaces or from heavy strain on the tibialis muscles can weaken and eventually fracture the tibia.

Most stress fractures occur in the bones of the lower leg and the foot. Tibial stress fractures commonly occur in gymnasts and basketball players who do extraordinary quantities of high-impact exercise. Metatarsal stress fractures of the foot are common in soldier recruits. Stress fractures are often the result of increasing the amount or the intensity of physical activity too rapidly.