A stress fracture is a relatively common happening in those who pursue sport and in military personnel who march and train vigorously. Stress fractures are mostly a feature of the lower limb bones but can be present in other areas of the body. The foot metatarsals, the fibula and the tibia show the greatest frequency of this type of injury, with decreasing likelihood further up the leg. The application of repetitive strains to the bone at a level insufficient to cause immediate fracture can do so over time as the activity proceeds.
During activity and exercise there may be an increased report of pain in the part, with patients typically noting they have recently made changes to their training regime's frequency or intensity. Treatment is typically without complication by reducing the person's activity or by immobilisation of the part. These fractures heal well in most cases although non-union is a possibility, in which case surgical fixation may be required. Once the fracture is surgically fixed the vast majority of cases heal well with suitable immobilisation.
Stress fractures happen when bone is repetitively loaded and this type of fracture is not usually the result of any particular traumatic occurrence. On being stressed with repeated tension or compression loads bone adapts by remodelling its structure and repairing the stress induced damage. If more of the microscopic damage to the bone occurs than can be repaired by the remodelling process then a fracture may occur. Significant increase in the person's recent physical training is a common theme.
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.
The important issues in being a risk for stress fracture are assumed to be the mechanical factors already mentioned but there may be many others such as a lower intake of calories, a lower bone density or osteoporosis, female gender and weakness of muscle. An increased incidence of stress fractures occurs in women who run a lot and these types of female athletes and others such as ballet dancers may have menstrual cycle alterations, bone density loss and a typically low body weight so they can easily pursue their activity.
A stress fracture typically comes on without much warning and often without severe symptoms, during an activity of repeated limb loading and without trauma. Resting will usually abolish the pain which will re-appear on performance of the weight bearing activity again. Tenderness and swelling may be apparent locally around the fracture site but it may be two to four weeks before a fracture can be discernible on x-ray. Bone scanning may detect fractures much earlier, within 72 hours of the incident, but are less clear as to the exact cause.
The usual management of stress fractures is conservative care, with the simplest and often the most effective method being a reduction in the responsible activity for 4 to 6 weeks. If there is a significant degree of pain on weight bearing then they can be placed in a brace, a rigid walking boot or a below knee cast, with crutch use as required. Orthoses in the shoes have been studied and found to allow a reduction in fracture incidence of a certain amount, with shock absorbing insoles having less clear benefits but potential.
Most commonly these fractures heal well and without complications but there can be problems with non-union in some particular areas. The base areas of the second and the fifth foot metatarsals are areas which can suffer from poor healing and which should be followed up for more prolonged immobilisation or surgical intervention if they do not heal.
