Family doctor

What are stress fractures?

Referred to as the occupational overuse injury of the "sportsperson's bones", stress fractures are under-diagnosed. Analogous to metal fatigue in aircraft wings, these injuries do not occur from one sudden traumatic event but rather from accumulation of stresses to an area of bone over a period of time.

The bones affected can be quite specific to the sport. Sports which may predispose to low back stress fractures are cricket, gymnastics, volleyball, swimming and ballet.

The most common group of athletes presenting with stress fractures are runners and people in those sports where running forms a major part of the fitness training. Historically in the clinic we've always seen a barrage of stress fractures leading up to the Rotorua Marathon and other long distance running events.

The common sites for the runner and sports involving a lot of running, are the two shinbones (tibia and fibula), the metatarsals (long bones of the feet) and some of the smaller bones forming the arch of the foot (e.g. navicular).

What symptoms suggest a stress fracture?

The gradual onset of pain/ache with exercise and persisting after exercise. Pain is usually worse with loading activities, e.g. hopping on the affected leg.

Stress fractures occur nearly always from doing "too much too soon". Sudden increases in mileage, training intensity or terrain difficulty can nearly always be traced in a runner's history.

How can stress fractures be prevented?

Bones only adjust to increases in stress very gradually. This requires a continual process of bone remodelling as bone breaks down under the stress of training. If the rate of breakdown exceeds the rate of remodelling, micro-fractures start occurring. If the level of training is not reduced at this stage then these microfractures may coalesce to form a stress or even a complete fracture.

Following the 10 % rule means not increasing your total distance, intensity, and time spent training by more than 10% in any given week. This would definitely reduce the frequency of stress fractures as it is thought that the skeletal system can only cope with this level of increase in training load.

Poor equipment can be involved in the onset of stress fractures. Worn-out shoes, or changing to a shoe with reduced shock absorption or to a shoe not appropriate for a particular foot-type, may mean a runner is less able to cope with their running load.

Other concerns

Another group that we are increasingly aware of these days is the athlete with an eating disorder who may through a combination of anorexia or bulimia and subsequent loss of menstrual periods have reduced bone density. Bone density is directionally proportional to bone strength and reduced bone density may be associated with an increased incidence of stress fracture.

Diagnosis

There is still a common misconception that these injuries always show up on x-rays. This is far from the truth and unfortunately many athletes have been informed that they can continue participating because they don't have a stress fracture on the basis of normal x-rays. Many of the common stress fractures are very seldom seen on an x-ray. Their exclusion requires a triphasic bone scan which involves injection of a radioisotope dye with pictures taken two hours later. A hot spot on bone scan indicates increased blood supply in that area and with the right history, is very suggestive of a stress fracture. Some may require further imaging such as CAT or MRI scans to confirm diagnosis.

What is the treatment?

The good news is that most stress fractures don't need to be immobilised in plaster. As long as the stress that caused them is removed, they will usually heal within six to ten weeks or more, depending on the bone involved. In that time the athlete can still maintain aerobic fitness and can usually cycle, swim or aqua jog in the case of a lower limb fracture. Stress fractures occurring in the femoral neck or back are two examples of stress fractures requiring a lot longer to heal.

Stress fractures in some sites do need to be completely immobilised.

Conclusion

With improved awareness of the cause of many of these stress fractures and easier diagnosis through appropriate scanning, they should occur less frequently and be diagnosed earlier. A correct early diagnosis is essential to avoid complications such as ununited fractures and surgery.

If you suspect your symptoms may be due to a stress fracture, it is important to consult a doctor knowledgeable about sporting injuries.