Stress Fractures of Bone
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.
The affected area may be the source of increasing pain levels during exercise and activity, with the sufferer often reporting they have increased their training levels in intensity or frequency. Conservative treatment is usually straightforward with limitation of activity of the part and in some fractures immobilisation is required. Healing is often also straightforward although there is the danger of non-union in some fractures, with some needing internal fixation. Orthopaedic fixation and careful immobilisation will lead to healing in the vast majority of cases.
These types of fractures occur because bone has been loaded again and again and there is rarely any specific traumatic event responsible for the fracture. Bones remodel to reinforce themselves when they are subjected to loads involving tension or compression, with minor damage of the bone occurring due to the stresses. If the remodelling process gets behind as the microscopic bone damage occurs then a fracture can result. The most common occurrence is for the person to have significantly increased their activities recently.
Risk factors for this injury include the elevation in how often the stresses occur, the raising of the strength of those stresses or a change in the tissue areas to which the forces are being applied. If the cross sectional area of bone which is being stressed is smaller then this will cause an increase in the stresses through that area, or the area can stay the same and the force be increased. Jumping and running are activities with a higher risk along with changes in the way activities are performed or the type of surface used.
Many of the mechanical factors are presumed to be the important issues in stress fracture but there may be many others including changes in diet with low calorie intake, reduced bone density or osteoporosis, muscle weakness, being female and perhaps a series of other factors. Female runners have a particularly high incidence of this kind of injury as they may have restricted calorie intake, changes in their menstrual cycle and reduction in density of bone, typical in sports people who have a low bodily weight like a ballet dancer.
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.