A stress fracture is one type of incomplete fracture in bones. It is caused by
"unusual or repeated stress." 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 metatarsals(bones of the foot).
It is a common sports injury, and most cases are associated with athletics.
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.
As with most conditions, a stress fracture is diagnosed with a history and
X-rays usually do not show any evidence of stress fractures, so a CT scan, MRI,
or bone scan may be more effective in unclear cases.
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 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 preinflated
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 may be needed for proper healing. The
procedure may involve pinning the fracture site, and rehabilitation can take up to
a half year.
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.
Consider a human runner. With each stride, large forces are exerted at various
places in the legs. Each shock—a rapid acceleration and energy transfer—must
be absorbed. Both muscles and bones serve as shock absorber. 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.
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
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.