Metatarsal Stress Fractures:
Perhaps the most common stress fracture in the runner is that of the metatarsal, the long, slender bone that connects the midfoot to the toes. There are actually five metatarsals, the first one being that of the first ray, or great toe, with the fifth being that of the small toe. Stress fractures most commonly occur within the fourth metatarsal.
A stress fracture of a bone happens because of excessive force, usually of a repetitive or cyclical nature. Each individual force is of little or no consequence to the bone, but sometime numerous "cycles" of such force are more than the microscopic architecture of the bone can bear. Tiny layers of bone fail in a serial fashion, one by one. Early, healing may be able to keep pace, but if repetitive forces continue, cracks propagate, and a true fracture occurs. The entire process is analogous to breaking a paper clip by bending it over and over again. With time, after a certain number of bending cycles, the structure fatigues.
Diagnosis is usually easy to make, as the injured runner typically has pain well-localized to the midfoot during and after running activities, especially on the top, or "dorsum", of the midfoot. The foot may feel "stiff" or "full", and other descriptions I have heard include "burning" or "numbness". There is almost always pin-point tenderness along the bone, and not in between the bones. Swelling is common, although often subtle. A limp might be present, more prominent after running. Usually the pain is minimal during rest or walking, and may even be absent early in the run, coming on only later. If neglected, the pain will typically get worse, occurring earlier and earlier during runs, and usually affecting performance in a progressive fashion.
X-rays can be, and often are, negative, especially within the first three weeks after onset of symptoms. Since the fracture is usually microscopic early, it is likely too small of a crack for the resolution of an X-ray study to detect. Often we might see healing on the film before a fracture line. A bone scan or MRI test may be helpful to make a definitive diagnosis in this "acute" stage. However, these expensive tests are not always necessary. A doctor with experience with these injuries can usually make the diagnosis by clinical suspicion alone. The history provided by the patient is often one of increasing or high running mileage or intensity, high-mileage old footware lacking residual cushioning, running on hard surfaces, etc., and physical findings are very specific.
The treatment of choice, of course, is rest. Oral and topical medicines, ice, orthotics, stretching, and the like will not solve the problem, but rather only minimize the symptoms. Without rest, healing cannot take place. Early in the course of the injury, successful healing may occur merely by restricting mileage and intensity, or by switching to softer running surfaces or a treadmill. However, as the fracture worsens, it will become necessary to avoid running all together, in favor of cycling, swimming, or pool running. Casts and crutches can almost always be avoided, as the symptoms quickly respond to rest and normal walking, unless the injury is neglected and running continues for a prolonged period.
Dan Wnorowski, M.D.