This article is about stress fractures in bones. For stress fractures in engineering, see fracture

Fracture

A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...

 and fatigue (material)

Fatigue (material)

'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue occurs...

.

A stress fracture is one type of incomplete fracture

Fracture

A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...

 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

Bone

Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

; this is why it is sometimes dubbed "hairline fracture". It typically occurs in weight-bearing bones, such as the tibia

Tibia

The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....

 (bone of the lower leg) and metatarsals (bones of the foot).

It is a common sports injury, and most cases are associated with athletics.

Presentation

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

Weight bearing

In orthopedics, weight-bearing is the amount of weight a patient puts on the leg on which surgery has been performed. In general, it is described as a percentage of the body weight, because each leg of a healthy person carries the full body weight when walking, in an alternating fashion.After...

. 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.

Diagnosis

As with most conditions, a stress fracture is best diagnosed after interview and examination by a physician. Investigations are not necessary to diagnose a stress fracture.

X-rays usually do not show any evidence of stress fractures, so a CT scan, MRI, or 3-phase bone scan

Bone scan

A bone scan or bone scintigraphy is a nuclear scanning test to find certain abnormalities in bone which are triggering the bone's attempts to heal. It is primarily used to help diagnose a number of conditions relating to bones, including: cancer of the bone or cancers that have spread to the bone,...

 may be more effective in unclear cases.

Treatment

If a stress fracture occurs in a weight-bearing bone, healing will be delayed or prevented by continuing to put weight on that limb.

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 is 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

Physical therapy

Physical therapy , often abbreviated PT, is a health care profession. Physical therapy is concerned with identifying and maximizing quality of life and movement potential within the spheres of promotion, prevention, diagnosis, treatment/intervention,and 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

Orthopedic cast

An orthopedic cast, body cast or surgical cast, is a shell, frequently made from plaster, encasing a limb to hold a broken bone in place until healing is confirmed...

 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.

With severe stress fractures, surgery

Surgery

Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...

 may be needed for proper healing. The procedure may involve pinning

Percutaneous pinning

Percutaneous pinning is a technique used by orthopedic surgeons for the stabilisation of unstable fractures.Many fractures can be manipulated into wholly satisfactory positions, immobilized in an appropriate cast and allowed to heal. Some fractures, however, cannot be held in a satisfactory...

 the fracture site, and rehabilitation can take up to a half year.

Causes

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 osteoblast

Osteoblast

Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...

s 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

Muscle fatigue

Muscle fatigue is the decline in ability of a muscle to generate force. It can be a result of vigorous exercise but abnormal fatigue may be caused by barriers to or interference with the different stages of muscle contraction...

 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.

Frequency

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

Black people

The term black people is used in systems of racial classification for humans of a dark skinned phenotype, relative to other racial groups.Different societies apply different criteria regarding who is classified as "black", and often social variables such as class, socio-economic status also plays a...

 African descent than in Caucasians

Caucasian race

The term Caucasian race has been used to denote the general physical type of some or all of the populations of Europe, North Africa, the Horn of Africa, Western Asia , Central Asia and South Asia...

, 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

Female athlete triad

Female Athlete Triad is a syndrome in which eating disorders , amenorrhoea/oligomenorrhoea and decreased bone mineral density are present. Also know simply as the Triad, this condition is seen in females participating in sports that emphasize leanness or low body weight...

 also can put women at risk, as disordered eating and osteoporosis can cause the bones to be severely weakened.

Prevention

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

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 and vitamin D

Vitamin D

Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

 intake, depending on the individual. Also, it is important to monitor diet, because nutrition

Nutrition

Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....

 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

Creighton University

Creighton University is a private, coeducational, Jesuit, Roman Catholic university located in Omaha, Nebraska, United States. Founded by the Society of Jesus in 1878, the school is one of 28 member institutions of the Association of Jesuit Colleges and Universities. The university is accredited by...

 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 Sunday, Feb. 11, 2007 at the 53rd annual Orthopaedic Research Society

Orthopaedic Research Society

The Orthopaedic Research Society is an organization dedicated to advancement of orthopaedic research. The ORS carries out this mission through education in research, dissemination of research knowledge, advocacy for increasing of resources for research, and increasing awareness of the importance...

 meeting at the San Diego Convention Center

San Diego Convention Center

The San Diego Convention Center is the primary convention center in San Diego, California. It is located in the Marina district of downtown San Diego near the Gaslamp Quarter, at 111 West Harbor Drive...

.

Dinosaurs

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

Trauma (medicine)

Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...

. 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

Pathognomonic

Pathognomonic is a term, often used in medicine, that means characteristic for a particular disease. A pathognomonic sign is a particular sign whose presence means that a particular disease is present beyond any doubt...

" 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

Osteomyelitis

Osteomyelitis simply means an infection of the bone or bone marrow...

 without difficulty because of a lack of bone destruction in stress fracture lesions. They can be distinguished from benign bone tumors like osteoid osteoma

Osteoid osteoma

An osteoid osteoma is a benign bone tumor which arises from osteoblasts and originally thought to be a smaller version of an osteoblastoma. Osteoid osteomas tend to be less than 1.5 cm in size. The tumor can be in any bone in the body but are most common in long bones, such as the femur and tibia....

 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

Hyperparathyroidism

Hyperparathyroidism is overactivity of the parathyroid glands resulting in excess production of parathyroid hormone . The parathyroid hormone regulates calcium and phosphate levels and helps to maintain these levels...

 or hyperthyroidism

Hyperthyroidism

Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...

 was found in the specimens, either.

After examining the bones of many kinds of dinosaur the researchers noted that Allosaurus

Allosaurus

Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...

had a significantly greater number of bulges on the shafts of its hand and foot bones than the tyrannosaur Albertosaurus

Albertosaurus

Albertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...

, or the ostrich dinosaurs Ornithomimus

Ornithomimus

Ornithomimus is a genus of ornithomimid dinosaur from the Late Cretaceous Period of what is now North America.In 1890 Ornithomimus velox was named by Othniel Charles Marsh on the basis of a foot and partial hand from the Maastrichtian Denver Formation. Another seventeen species have been named since...

and Archaeornithomimus

Archaeornithomimus

Archaeornithomimus is a genus of ornithomimosaurian theropod dinosaur from the Late Cretaceous of China, 70 million years ago....

. 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.

External links

• MedPix Radiology Diagnosis of Stress Fracture
• Macrorad Teleradiology Ischial Stress Fracture