Stress fractures are a common occurrence particularly in sporting endeavours and in recruits in the armed services, with overuse of the lower limbs a common theme. The lower leg is the most frequently affected area but other parts, even the arms, can be affected. The tibia, fibula and metatarsals are the most obvious areas to suffer, with further up the lower limbs much less commonly occurring. Repetitive stresses to the bones of a level not sufficient to cause direct fracture are the underlying cause of this injury.
Increasing levels of pain reported in the part during activities or exercise is the typical pattern of presentation, with a recent upturn in the intensity or frequency of training often reported. Treatment is uncomplicated and involves reducing the levels of activity and in some cases by immobilisation. Most heal without problems but there are some fractures which are much more likely to suffer from non-union and for which surgical intervention may be required. With orthopaedic surgery and formal immobilisation these fractures will eventually heal.
A stress fracture is likely to occur when bone is stressed many times in a similar manner, mostly without any particular individual event occurring. As repetitive compression and tension stresses are applied to the bone it sustains micro-damage which is repaired continually by the bone remodelling process. If the bones sustain increased levels of microscopic injury they may not be able to repair themselves quickly enough by remodelling and strengthening, leading inevitably to fracture. Increased physical activity is a common factor in these injuries.
Factors which increase the likelihood of a fracture occurring are reducing the bone area across which the stresses are acting, increasing the absolute levels of force and making the application of such stresses more frequent. The cross-sectional area of the bone is the factor determining the results of force applied, a smaller area meaning a higher order of force is suffered by the bone. Or the force could be increased in itself. Typical examples of risky activities are jumping or running, with other risks being changes in the exercise surface and techniques used.
Additional factors could be risk factors such as reduced bone density, dietary changes, weakness or other mechanical factors as the other factors are all mostly presumed to be the key ones. Scientific research has indicated being female, having a low body weight, poor diet and many other factors may be important. Female runners are particularly at risk, with reduced caloric intake, disturbances in menstrual cycle and lower bone density presenting in such athletes and others who require a low body weight such as ballet dancers.
The most common onset for a stress fracture is low profile and without high pain levels, typically following repeated bearing of weight on a part of the foot or leg and without any incident. The pain will resolve when the patient takes their weight off the part and re-occur when they once again repeat the typical movement. Local palpation of the injured areas may show oedema and pain or tenderness but there may be a lapse of between 2 and 4 weeks before a fracture can show up on an x-ray. Earlier detection of fractures may be possible with bone scanning.
Stress fractures are mostly treated with conservative methods, the most effective and the most straightforward being to limit the aggravating functional activity responsible for a period of four to six weeks. If weight bearing causes significant pain then it can be restricted by using elbow crutches with a rigid walking boot, brace or below knee plaster cast. Studies have been done on wearing corrective orthoses in shoes and there is some evidence they can reduce the incidence of stress fractures, with some potential benefits from shock absorbing insoles
Stress fractures in most areas of the body heal without complications but in some cases healing can be delayed or not occur at all, so-called non-union. Delayed or non-union is more common in certain areas such as the bases of the second and fifth metatarsals in the feet. Routine review of these fractures is important to assess whether further immobilisation or internal fixation is needed.