A stress fracture is a small crack in a bone that occurs when bone tissue has to absorb more weight and impact than it can handle. This type of injury can occur over time in a well-conditioned bone that is overused, or suddenly in an underconditioned bone that is placed under undue stress in a short period.1 Stress fractures most frequently occur in the feet, ankles, and lower legs, though they can also occur in other parts of the body, such as the pelvis, hip, ribs, sacrum, clavicle, and upper extremities (arms).

Stress fractures can affect many different types of athletes, but they are most common in those who participate in activities involving heavy, repetitive impact on the feet and lower legs, such as long-distance running, track and field, tennis, dancing, gymnastics, basketball, and soccer. The injury is common, comprising up to 15 percent of all sports-related injuries.

How a stress fracture happens

Like most tissues in the body, bone is constantly renewing and replacing itself—a process called bone remodeling. Weight-bearing exercise that places moderate levels of stress on the bones is one way to further stimulate bone-tissue renewal and to increase bone density.2 An interesting example that illustrates the importance of weight load on bone density is the significant decrease in bone density seen in astronauts after spending time away from Earth.

However, if a bone absorbs so much weight and/or impact stress in a short period of time that the normal remodeling process cannot keep up, an imbalance develops between bone damage and bone remodeling.2

In an imbalance situation, instead of the bone becoming stronger and denser due to moderate exercise, the bone becomes thinner and weaker as it becomes overloaded, a phenomenon called bone fatigue. Bone fatigue is often expedited by muscle fatigue, in which muscles that normally serve a stabilizing role become fatigued, causing instability that transfers stress to the bones.

The body typically adds new bone cells during rest periods, so the mix of intense exertion without adequate rest causes this imbalance to develop.7

Common situations that may trigger a bone-stress imbalance include:

  • Runners who extend their daily mileage totals too quickly (for example, faster than the “two-mile-a-week rule,” which governs how much runners should add to their single-session running distances each week)
  • Ballet dancers who train ten to twelve hours a day for an upcoming performance without adequate rest periods
  • Military recruits doing marching drills during basic training

During a bone-stress imbalance, the bone first undergoes a stress reaction that an athlete may feel as a mild ache in the affected bone, or not at all. This indicates that the bone tissue is damaged on a microscopic level.3 If the stress imbalance continues, that microscopic damage may become more significant, to the point it can be detected on clinical examination.

A stress fracture is also known as a hairline fracture because the bone remains essentially intact around the thin crack formed by the stress reaction. If a stress fracture remains untreated, however, the affected bone(s) may break completely, a far more serious type of injury.7,8,9

This article provides a detailed overview of stress fracture causes, symptoms, risk factors, and treatments.

Stress Fracture Symptoms

The primary symptom of a stress fracture is pain and tenderness at the fracture site, though some stress fractures produce little to no symptoms at all until they progress to a more serious injury, such as a displaced fracture.

Symptoms of stress fracture include, but are not limited to:

Nagging, aching pain that is felt deep within the foot, toe, ankle, shin, hip, or arm. The exact source of the pain may be difficult to pinpoint, such as a general ache in the entire foot or lower leg.13

Dull pain that disappears with rest but resumes with activity or weight-bearing. For example, pain in the foot or ankle that appears when the foot strikes the ground while running or dancing, but disappears after the exercise sessions end, or pain in the elbow or shoulder that only occurs when throwing or receiving a ball. The pain may not start at the beginning of the exercise, but may develop at the same point during the activity.

A general feeling of weakness in a foot, ankle, or limb, with or without pain. A runner may suddenly be unable to match previous speeds or distance without feeling exhausted or having a leg give out, though it is less likely that this happens without some at least some pain.

Tenderness and swelling. The soft tissue around a stress fracture may become swollen and tender to the touch. Bruising may also be present, though this is rare for most stress fractures until they become severe.

Localized pain at night. Pain in a certain area, such as the foot, ankle, or hip that appears in the evening is often associated with stress fractures, even if the pain is not debilitating during sports activities.

Pain that does not improve with rest or RICE protocol. Pain that resumes or remains constant despite taking time off to rest and/or using the RICE (rest, ice, compression, and elevation) protocolmay be due to a stress fracture or other causes.

Pain in the back or sides. Nagging pain in the trunk can sometimes be an indicator of stress fractures in the rib cage and/or sternum, which can occur in athletes who participate in sports such as rowing, tennis, or baseball.

Pain that progressively worsens over time. Pain that starts out as a dull ache which once only appeared during sports activity but has become constant and debilitating may be an indication of a developing stress fracture.15 Another concern is when a young, healthy patient requires crutches because of lower-extremity pain that developed gradually, as this can be a sign of a stress fracture.

Pain that appears shortly after a change in activity. Nagging pain that appears within 7 to 10 days of a significant increase in strenuous activity—such as enrolling in military boot camp—is frequently associated with stress fractures.

Because stress fractures often only improve with rest, any athlete who experiences symptoms that indicate a possible stress fracture is advised to take a break from sports activity and see a doctor trained in sports medicine for an accurate diagnosis and treatment plan.

Stress Fracture Causes

Bone health in athletes requires an adequate balance between exertion and rest, as well as good nutrition and proper training form. Athletes also must train in a manner that allows their bodies enough time to adjust to increased levels of exertion in order to avoid injury. If any one of these areas is neglected, stress fractures may develop.

The following are some of the underlying causes of stress fracture development in athletes. Many athletes experiencing stress fractures will have multiple root causes that will need to be addressed before healing and a return to sports can commence.

It is also possible for non-athletes to develop stress fractures during normal daily activities if they have poor bone density due to a condition that weakens the bone, such as osteoporosis or osteopenia.

Changes in exercise patterns

Stress fractures may occur if athletes rapidly increase their level of activity in one or more of the following ways:

Exercise frequency. Athletes who increase their number of exercise sessions without giving their bodies adequate time to adjust may develop stress fractures. For example, recreational runners who are accustomed to running two or three times a week may develop stress fractures in the feet, ankles, or shins if they abruptly change to a six-day-a-week schedule.4

Exercise duration. Increasing the length of individual exercise sessions too quickly can lead to stress fractures. For example, a ballet dancer accustomed to daily 30-minute practice sessions may develop stress fractures if she increases her session length to 90 minutes or more.

Exercise intensity. Even if athletes do not change the frequency or duration of their regular workouts, a change in the level of exertion in those workouts can still lead to stress fractures if the body is not given enough time to adjust to the new level of intensity. For example, recreational athletes who are accustomed to three moderate, 30-minute sessions on an elliptical trainer each week might experience stress fractures if they switch to three intense, 30-minute sessions of sprints mixed with plyometrics.4 This same phenomenon can occur when athletes dramatically increase their speed, such as increasing the distance an athlete runs over a 30-minute period.

Change of playing surface. Athletes who have grown accustomed to one type of playing surface may develop stress fractures if they make a switch to a new type of playing surface. Examples include switching from grass to clay tennis courts, changing from natural grass to artificial turf, or running outdoors after running on a treadmill all winter.

Change in daily footwear or stepping habits. Sometimes a simple change in footwear and/or amount of walking activity is all that is required to cause a stress fracture. For example, changing from flat shoes to wearing high heels on a daily basis, or a normally sedentary person walking a lot while touring on vacation.

Athletes and anyone else who engages in exercise are advised to ramp up their activities gradually to reduce the risk of stress fracture.

Poor conditioning or training techniques

In addition to the above factors, athletes who lack the athletic conditioning to take on a certain level of sports activity or “overdo it” in a single sport may develop stress fractures, due to lack of cross-training. For example:

Not maintaining a consistent training regime. Athletes who expect to return to their peak-season level of conditioning after the off-season risk developing stress fractures. For example, distance runners who ran a marathon(s) at the end of the fall but only did short 3-to-5-mile training runs during the winter can develop a stress fracture if they try to replicate their previous mileage when the spring running season starts.

Playing the same sport all the time. Year-round athletes who do not change sports with each passing season may develop stress fractures, especially during the childhood and adolescent years. For example, a teenage soccer player who plays on his high school team in the fall, then joins independent traveling teams in the winter and spring, then goes to soccer camp in the summer without ever taking a break from the sport.

Not using the right equipment or using worn-out equipment.Playing sports with old, worn-out equipment, ill-fitting equipment, or no equipment at all can result in stress fractures. For example, a ballerina may develop stress fractures in her toes and/or metatarsals if she dances in worn-out toe shoes, or a recreational runner may develop stress fractures if he chooses cheap running shoes that do not provide adequate arch support.

Poor technique. Athletes who do not follow established techniques when playing their sport can develop stress fractures. For example, gymnasts with sloppy landing techniques, dancers who “cheat” their foot positions, or track athletes who have trouble clearing hurdles. Stress fractures related to poor technique are especially common among recreational athletes and early-career athletes.

Poor bone density

Early-onset osteoporosis in adolescent girls and/or elite female athletes related to high levels of athletic intensity and poor nutrition can cause stress fractures. This phenomenon is often called the female athletic triadand it commonly occurs among female athletes who participate in sports where low body weight offers a competitive advantage, such as ballet, distance running, figure skating, or gymnastics.

In the female athletic triad, female athletes may engage in disordered eating (anorexia/bulimia) combined with intense levels of exercise in order to maintain a low body-fat percentage. Disordered eating and intense physical activity can suppress the hormones that control the menstrual cycle (amenorrhea), a biochemical state similar to menopause that results in the lack of a regular menstrual periods. This can rob the bones of calcium, weakening them and increasing the chance of stress fractures.

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