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|Classification and external resources|
|ICD-9||733.93, 733.94, 733.95|
|eMedicine||radio/783 orthped/446 pmr/134|
- This article is about stress fractures in bones. For stress fractures in engineering, see fracture and fatigue (material).
A stress fracture is one type of incomplete fracture in bones. It is caused by "unusual or repeated stress" and also heavy continuous weight on the ankle or leg. This is in contrast to other types of fractures, which are usually characterized by a solitary, severe impact.
It could be described as a very small sliver or crack in the bone; this is why it is sometimes dubbed "hairline fracture". It typically occurs in weight-bearing bones, such as the tibia (bone of the lower leg), metatarsals (bones of the foot), and less commonly, the femur.
Stress fractures usually have only a few symptoms. A stress fracture could present as a generalized area of pain and tenderness associated with weight bearing. Usually when running, a stress fracture in the leg or foot will cause severe pain at the beginning of the run, moderate pain in the middle of the run, and severe pain at the end and after the run. After running it may just feel like shin splints, but in a very concentrated area. Occasionally, darkening or bruising will be seen at the site.
A stress fracture is best diagnosed after interview and examination by a physician. Investigations are not necessary to diagnose a stress fracture.
If a stress fracture occurs in a weight-bearing bone, healing will be delayed or prevented by continuing to put weight on that limb. Most people don't even know they have a hairline fracture until they hurt themselves again, then they have a broken bone. If left untreated, the broken bone can turn into an infection that can cause severe medical issues.
Rest is the only option for complete healing of a stress fracture. The amount of recovery time varies greatly depending upon the location, severity, the strength of the body's healing response and an individual's nutritional intake. Complete rest and a cast or walking boot are usually used for a period of four to eight weeks, although periods of rest of twelve to sixteen weeks are not uncommon for more severe stress fractures. After this period activities may be gradually resumed, as long as the activities do not cause pain. While the bone may feel healed and not hurt during daily activity, the process of bone remodeling may take place for many months after the injury feels healed, and incidences of re-fracturing the bone is still at significant risk. Activities such as running or sports that place additional stress on the bone should only gradually be resumed. One general rule is to not increase the volume of training by more than 10 percent from one week to the next.
Rehabilitation usually includes muscle strength training to help dissipate the forces transmitted to the bones.
Bracing or casting the limb with a hard plastic boot or air cast may also prove beneficial by taking some stress off the stress fracture. An air cast has pre-inflated cells that put light pressure on the bone, which promotes healing by increasing blood flow to the area. This also reduces pain because of the pressure applied to the bone. If the stress fracture of the leg or foot is severe enough, crutches can help by removing stress from the bone.
Bones are constantly attempting to remodel and repair themselves, especially during a sport where extraordinary stress is applied to the bone. Over time, if enough stress is placed on the bone that it exhausts the capacity of the bone to remodel, a weakened site—a stress fracture—on the bone may appear. The fracture does not appear suddenly. It occurs from repeated traumas, none of which is sufficient to cause a sudden break, but which, when added together, overwhelm the osteoblasts that remodel the bone.
Stress fractures commonly occur in sedentary people who suddenly undertake a burst of exercise (whose bones are not used to the task). They may also occur in Olympic-class athletes who do extraordinary quantities of high-impact exercise, in professional and amateur distance runners who run high weekly mileage, or in soldiers who march long distances.
Muscle fatigue can also play a role in the occurrence of stress fractures. In a runner, each stride normally exerts large forces at various points in the legs. Each shock—a rapid acceleration and energy transfer—must be absorbed. Both muscles and bones serve as shock absorbers. However, the muscles, usually those in the lower leg, become fatigued after running a long distance and lose their ability to absorb shock. As the bones now experience larger stresses, this increases the risk of fracture.
Previous stress fractures have been identified as a risk factor.
Dr Johnathan C Reeser states that, in the US, the annual incidence of stress fractures in athletes and military recruits ranges from 5% to 30%, depending on the sport and other risk factors. Stress fractures occur less frequently in those of black African descent than in Caucasians, due to a generally higher BMD (bone mineral density) in the former. Women and highly active individuals are also at a higher risk. The incidence probably also increases with age due to age-related reductions in BMD. But children may also be at risk because their bones have yet to reach full density and strength. The female athlete triad also can put women at risk, as disordered eating and osteoporosis can cause the bones to be severely weakened.
One method of avoiding stress fractures is to add more stress to the bones. Though this may seem counter-intuitive (because stress fractures are caused by too much stress on the bone), moderate stress applied to the bone in a controlled manner can strengthen the bone and make it less susceptible to a stress fracture. An easy way to do this is to follow the runner's rule of increasing distance by no more than 10 percent per week. This allows the bones to adapt to the added stress so they are able to withstand greater stress in the future.
Strengthening exercises also help build muscle strength in the legs. Strengthening these muscles will prevent them from becoming fatigued quickly, allowing them to absorb the strain of running for longer periods of time. Key muscles that need strengthening with lower leg stress fractures are the calves and the shin muscles. Runners often suffer from overuse injuries or repetitive stress injuries. These include stress fractures, stress reactions, tendinitis, meniscal tears, ITB Friction syndrome, and exacerbation of pre-existing arthritis. Stress fractures, if not diagnosed and treated, can develop into complete fractures.
Depending on a variety of factors (including weight, running surface and shoe durability), runners should replace their shoes every 300–700 miles to allow adequate mid-sole cushioning. A change in running surfaces can also help prevent stress fractures. However, it is also argued that cushioning in shoes actually causes more stress by reducing the body's natural shock-absorbing action, increasing the frequency of running injuries.
During exercise that applies more stress to the bones, it may help to increase calcium and vitamin D intake, depending on the individual. Also, it is important to monitor diet, because nutrition plays a vital role in bone development. Some individuals are at risk of osteoporosis, and depending on the country in which medical care is being supplied, there may be an osteoporosis screening program available.
A study released by Creighton University has shown Calcium and Vitamin D supplementation, even over a short period, can significantly reduce stress fractures in female military recruits. The study results were reported on February 11, 2007 at the 53rd annual Orthopaedic Research Society meeting at the San Diego Convention Center.
Occurrence in non-humans 
In 2001, Bruce Rothschild and other paleontologists published a study examining evidence for stress fractures in theropod dinosaurs and analyzed the implications such injuries would have for reconstructing their behavior. Since stress fractures are due to repeated events they are probably caused by expressions of regular behavior rather than chance trauma. The researchers paid special attention to evidence of injuries to the hand since dinosaurs' hind feet would be more prone to injuries received while running or migrating. Hand injuries, meanwhile, were more likely to be caused by struggling prey. Stress fractures in dinosaur bones can be identified by looking for bulges on the shafts of bones that face toward the front of the animal. When x-rayed, these bulges often show lines of clear space where the x-rays have a harder time traveling through the bone. Rothschild and the other researchers noted that this "zone of attenuation" seen under the x-ray typically cannot be seen with the naked eye.
The researchers described theropod phalanges as being "pathognomonic" for stress fractures, this means they are "characteristic and unequivocal diagnostically." Rothschild and the other researchers examined and dismissed other kinds of injury and sickness as causes of the lesions they found on the dinosaurs' bones. Lesions left by stress fractures can be distinguished from osteomyelitis without difficulty because of a lack of bone destruction in stress fracture lesions. They can be distinguished from benign bone tumors like osteoid osteoma by the lack of a sclerotic perimeter. No disturbance of the internal bony architecture of the sort caused by malignant bone tumors was encountered among the stress fracture candidates. No evidence of metabolic disorders like hyperparathyroidism or hyperthyroidism was found in the specimens, either.
After examining the bones of many kinds of dinosaur the researchers noted that Allosaurus had a significantly greater number of bulges on the shafts of its hand and foot bones than the tyrannosaur Albertosaurus, or the ostrich dinosaurs Ornithomimus and Archaeornithomimus. Most of the stress fractures observed along the lengths of Allosaurus toe bones were confined to the ends closest to the hind foot, but were spread across all three major digits in "statistically indistinguishable" numbers. Since the lower end of the third metatarsal would have contacted the ground first while a theropod was running it would have borne the most stress and should be most predisposed to suffer stress factors. The lack of such a bias in the examined fossils indicates an origin for the stress fractures from a source other than running. The authors conclude that these fractures occurred during interaction with prey. They suggest that such injuries could occur as a result of the theropod trying to hold struggling prey with its feet. The presence of stress fractures provide evidence for very active predation-based feeding rather than scavenging diets.
- "Stress fracture" at Dorland's Medical Dictionary
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- "Common Stress Fractures – October 15, 2003 – American Family Physician". Retrieved 2007-12-23.
- Kelsey JL, Bachrach LK, Procter-Gray E et al. (2007). "Risk factors for stress fracture among young female cross-country runners". Med Sci Sports Exerc 39 (9): 1457–63. doi:10.1249/mss.0b013e318074e54b. PMID 17805074.
- "eMedicine – Stress Fracture : Article by Jonathan C Reeser, MD, PhD". Retrieved 2007-12-23.
- Tara Parker-Pope (June 06, 2006). "Is Barefoot Better? Some Athletes Say Running Shoeless Benefits Body and Sole". The Wall Street Journal.
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- Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.
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