Stress Fractures
Stress Fractures occur when excessive repetitive force is applied to a localized area of bone. Activities such as walking and running subject the bones of the foot to large forces that often lead to microscopic cracks in the bone. Normally these microfractures heal, leading to a stronger bone. However, when the rate of loading on the foot is such that the body's healing response can not keep up then a stress reaction and eventually a stress fracture will occur.
Stress fractures occur in the same manner that you would break a paper clip -- excessive wiggling back and force will lead to breakage.
Stress fractures can occur in:
1. Normal bone that is subject to abnormally excessive repetitive loading.
An example of this would be a new army recruit going on a long march as part of basic training who as a result of this dramatic increase in repetitive loading develops a stress fracture (often called a "March" fracture).
2. Weakened bone that is subject to seemingly normal repetitive forces.
For example a person with thin bone (ex. osteoporosis) who walks much more than they are use to.
Stress fractures do not occur in random locations. They occur in the bones that are absorbing the excessive force. Each foot absorbs force in a slightly different manner that is dictated by the person's foot shape and gait pattern. Common sites of stress fractures in the foot include:
Diagnosis of a stress fracture requires a high degree of suspicion as the fracture often does not show up on the initial x-ray. Patients will usually report localized aching pain in the effected area. They will give a history of some increase in their normal activity level (ex. went for a long hike this weekend). They may have a history of a condition that predisposes them to weaker bones such as: Osteoporosis (weak thin bone); Amenorrhea (loss of normal menstrual cycle); or a smoking history
X-rays may initially be negative as it often takes 10 days or more for a callus (new bone) to form and be visualized on x-rays. Bone scans and MRIs will be positive. It is possible and in fact common to see bone edema on an MRI without having an outright stress fracture. This represents a "stress reaction" and is equivalent to microscopic bone fracturing without a complete stress fracture.
Treatment
Treatment of stress fractures generally involves:
1. Resting the effected area until the bone adequately heals, often 6-8 weeks or more.
2. Avoiding any precipitating activities.
3. Correcting any risk factor that may predispose to further stress fractures.
Edited September 15th, 2009