stress fracture A break that develops in bone because of fatigue failure rather than a sudden overwhelming force. This may occur in normal bone as a result of excessive forces or in abnormal bone as a result of everyday stresses. These are clearly different conditions, although the end result may look very similar.
Stress fractures in normal bone occur predominantly in athletes and soldiers. They result from forces applied repetitively to an area of bone. As a result of these forces remodeling of the bone occurs. This involves bone cells called osteoclasts eating away established bone followed by other bone cells called osteoblasts laying down new bone better able to withstand the forces being applied. This process is quite common in athletes. Those who develop a stress fracture are on one end of a spectrum where the osteoclastic activity is not followed by adequate repair. Predisposing factors include inadequate muscle strength or training beyond muscle exhaustion. Muscles normally contribute to the shock-absorbing capacity of the lower limb. When this is lost there is increased impact transmitted to bone. Stress fractures can also occur in the upper limbs, for example in baseball pitchers, simply due to the forces applied by muscle.
The most common cause of abnormal bones giving rise to stress fractures is osteoporosis. Patients with rheumatoid arthritis and osteoporosis seem to be at particular risk of stress fractures. This may relate to the deformities many rheumatoid patients develop, leading to abnormal stresses being put on bones as well as the high use of corticosteroids. Other bone diseases such as osteomalacia, paget's disease, and alcohol abuse are well-recognized causes. Some patients with hypermobility syndrome have bony fragility and develop stress fractures.
Pain is the predominant symptom. This is often exquisite when force is applied across the fracture, for example when standing or walking with a stress fracture in one of the leg bones. A few patients, however, have remarkably little pain and can continue to walk with a fracture through their hip bone. Since the bones are not displaced they are still able to take the person's weight. Typical sites of fracture in normal bones are the second metatarsal and tibia in athletes or soldiers. The metatarsal is the bone running down from the midfoot to the toe, and the fracture usually occurs nearer the toe. This is known as a march fracture. The area overlying the fracture is often slightly swollen, and pressing over it is extremely painful. The tibia (larger of the lower-leg bones) is more frequently affected in long-distance runners. The humerus or upper-arm bone may become involved in baseball pitchers.
in severe osteoporosis almost any bone may be involved, although some are more frequent. The lower end of the tibia, the neck of the femur (thighbone), and the outer part of the sacrum (lowest part of the spine) are typical areas in the lower half of the body. Ribs are often affected, and vertebral collapse in the spine may be seen as a stress fracture.
When a typical site is affected in an athlete the diagnosis is usually suspected immediately, often by the athlete. However, in a patient with active arthritis the lack of obvious trauma and presence of painful joints may lead to a stress fracture being overlooked initially. When it affects a long bone a very tender lump can often be felt at the fracture site. An X ray will confirm the diagnosis but may not show the fracture early on. if the X ray is negative, a tech-netium bone scan will show the lesion. CT and MRI scanning are also effective in demonstrating stress fractures but are seldom required. it is important to exclude osteomalacia, a bone disease caused by lack of calcium or vitamin D, and a pathological fracture caused by a tumor weakening the bone.
Relative rest and pain relief are required, and the fractures usually heal without specific treatment. For patients with a metatarsal fracture, for example, it is often adequate immobilization to wear a stiff shoe, although occasionally a plaster cast will be required. Attention to biomechanics and training schedules may be needed for athletes, and avoidance of running on hard surfaces or cambers is essential. in patients with osteoporosis or other bone disease, treatment of the underlying disease is obviously important.
calcitonin is effective in controlling the pain. This is given by injections under the skin and may cause flushing and diarrhea at the higher doses. The bisphosphonate group of drugs is also effective. These include pamidronate, alendronate, and rise-dronate. Most fractures heal within three to six months but may occasionally take longer.
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