Keywords

microfractures, stress fractures in runners, stress-related injuries

 

Authors

  1. Corrarino, Jane E. RN, DNP

Abstract

Abstract: Many runners in the United States are at risk for stress-related injuries, which are largely preventable. Severity and recovery vary, and can range from uneventful to surgical intervention. This article explores risks, pathophysiology, diagnostic considerations, and rehabilitation. Prevention strategies are also outlined.

 

Article Content

Physical activity is known to contribute to overall health and chronic disease prevention. As part of its physical activity guidelines, the CDC recommends that Americans should engage in at least 75 minutes a week of vigorous-intensity aerobic activity (such as running, jogging) and muscle strengthening activities (those encompassing all major muscle groups).1

  
Figure. No caption a... - Click to enlarge in new windowFigure. No caption available.

Approximately 43% of adults in the United States are aerobically active. It is estimated that at least 7% of these adults participate in running on a regular basis, translating into almost 7 million adult runners in the United States.2,3 Some of these runners are at risk to sustain running-related injuries, including stress fractures.

 

Pathology and pathogenesis

The skeletal system is the underpinning of human anatomy. Bones provide mechanical support related to movement, house hematopoietic essentials, and protect organs.

 

Bones are divided into two types: cancellous and cortical. Cancellous bones (trabecular) are located in the epiphysis and metaphysis of long bones (see A longitudinal section of a long bone). The majority of remodeling takes place in these types of bones. The increased turnover rate of these bones is the reason that bone mineral density (BMD) measurements are taken of cancellous bone (such as the neck of the femur). In these locations, changes in BMD are easier to identify. Cancellous bones are highly vascular and contain bone marrow. They have a higher surface area than cortical bone. Cortical bones, also known as compact bone, make up 80% of the skeleton, and are located in the shell of the tarsal bones and vertebral bodies, as well as the diaphysis of long bones. The metabolic turnover is eight times slower in cortical bones compared to cancellous bones. Most running-related stress fractures occur in the cortical bones.4

 

The maintenance of the skeleton is achieved through a dynamic cyclical remodeling process, which consists of constant bone breakdown and renewal, and most likely is initiated where and when fatigue and microscopic damage occur.5 Osteoclasts break down bone in response to fatigue and damage. They bind to the surface, and dissolve and digest the bone. Once this breakdown phase is completed, osteoblasts deposit new bone matrix and fill the lacunae back to the original level. In healthy bone, the osteoclastic bone breakdown portion of the cycle lasts approximately 3 weeks, as opposed to osteoblastic bone formation, which lasts about 3 months. The pathways involved in this process include the actions of cytokines as well as hormones such as calcitonin, vitamin D, parathyroid hormone, growth hormone, and steroids.4,5

 

Stress fractures

Bone changes its external form and its internal architecture in response to changes in function and form that are precipitated by stress. In other words, bone adapts to the loads it encounters. When repetitive stress occurs, osteoclasts surpass osteoblasts in activity, resulting in a short-term net weakening of the bone. In order to adapt to this stress and weakening, bone responds with new periosteal activity and new bone formation to supply reinforcement. If repetitive stress continues beyond the bone's capacity to adapt, osteoclast activity prevails and initially causes microfractures. This incremental failure is known as fatigue, and accumulation of these microfractures reduces resistance to fractures. Osteoblasts lag behind the breakdown activity of osteoclasts, leaving the bone susceptible to fatigue should repetitive stresses occur to the point where there is not enough time to rebuild bone.

 

These microfractures are seen as bone marrow edema on magnetic resonance imaging (MRI), and repeated stress influences their length, which is a significant parameter in bone resistance to fatigue. Muscles may also add to this stress by localizing forces over a small area of the bone and contributing to the mechanical stress on the bone. It is pertinent to note that bones respond to piezoelectric charges-that is, running-related forces precipitate electric charges that stimulate osteoblast/osteoclast activity. Essentially, these forces mechanically deform bone and alter electrical charges. These piezoelectric charges are created by collagen shearing forces and stimulate osteoclast activity.4 Most cortical bone stresses are tensional in nature. Thus, repetitive tensile forces stimulate osteoclasts over osteoblasts.

  
Figure. A longitudin... - Click to enlarge in new windowFigure. A longitudinal section of a long bone

Furthermore, it is believed that when muscle fatigue develops (markedly increasing running mileage over a short period of time), its protective shock-absorbing effect is reduced and higher forces are transmitted directly to the bone, thereby increasing microdamage.4 If overuse continues unimpeded without adequate rest and/or with excess strain, eventually a stress reaction and stress fracture can result within cortical bone.6,7 In contrast, fractures that occur in bones affected by a low BMD are also termed insufficiency fractures, and occur in circumstances such as osteoporosis, runners with the female athlete triad (disordered eating, amenorrhea, osteoporosis, discussed later in this article) or other metabolic bone disease. This type of fracture results from inadequate bone remodeling (increased bone breakdown and decreased bone formation) that occurs in reaction to a normal level of strain.

 

People who are physically active can be at risk to sustain a stress-related injury, including military recruits, ballet dancers, and runners. These injuries frequently occur in the lower limbs. A stress fracture is a fracture that occurs following a period of marked increase in physical activity involving new, repetitive loads and mechanical stress.8 This type of fracture is not associated with a single traumatic episode, but rather occurs over a period of time in weight-bearing bones. These fractures are associated with pain during activity and relieved by resting, and are the result of a series of biological responses to bone stress. Usually, there are no radiologic abnormalities during the early phases, and over time new periosteal bone formation may develop. The most frequently reported stress fracture sites are of the tibia, metatarsals, and fibula. These injuries are associated with at least a 30% increase in activity volume, training on an unyielding surface (for example, asphalt), or running in worn-out or unsuitable shoes.9,10 Fractures of the pelvis, first metatarsal sesamoid, and femur are reported less frequently. When affecting the femur, this type of fracture is typically located in the proximal third of the medial femoral cortex, which is an area subjected to excessive compression strain.11

 

Stress fracture risk

Certain factors are associated with an increased risk of stress fractures. These include lower bone density, menstrual disturbances, certain types of activity, and a marked increase in activity that results in significant increases in mechanical loading to the bone(s). It is important to note that risk factors do not cause this injury, but are factors that affect the remodeling process or the bone's mechanical environment, resulting in an increase in microdamage, a decrease in damage repair, or a combination of the two. The accurate identification of risk factors for stress injuries has been dampened by issues such as varying study design and sample selection. Most studies regarding stress fractures comprise case reports and case series. Many studies have limitations such as deriving incidence rates from those who have been treated at sports medicine clinics (referral bias). Other limitations include factors such as observation periods varying across studies, with ranges between 1 and 17 years, thus making it challenging to derive an accurate incidence of stress fractures and risks.9

 

Types of activity

Different types of activity can influence a person's risk of sustaining a stress fracture. One prospective study, conducted over a 10-year span, reported the incidence of stress-related injuries to bones in 6,000 athletes. In that particular study, 3.2% of runners sustained bone-related stress injuries, with women's reported rate slightly higher than men's.12 Another prospective study determined that 60% of athletes sustaining a stress fracture had a prior stress fracture history, with a recurrence rate of 12%.13 The stress fracture risk for athletes varies across sports, with the highest incidence for track and field and the lowest for soccer. The fact that recurrence rates may be relatively high might indicate that inadequate attention is paid to reducing modifiable risks subsequent to sustaining an initial stress fracture.

 

Running and jogging involve ground reaction forces that are three to eight times higher than those involved in walking; therefore, running puts a person at higher risk of stress fractures.4 Downhill running in particular has been documented to increase the stress that worsens the risk for sustaining a running injury.14 In addition, roads are typically made of very hard surfaces, and are typically angled on a downward slope both ways from the crown. Many road runners consistently run on the same side of a road (often facing traffic on the left side of the road). This running pattern has been implicated in increasing one's risk of stress-related injuries, including fractures.14-16 This pattern facilitates the leading leg (the one nearest the curb) absorbing the brunt of associated repetitive forces.

 

A significant relationship (P < 0.01) has been demonstrated between fracture sites and type of activity.17 Runners are more likely to sustain a stress-related pelvic or long bone (femur, tibia, and fibula) fracture. In addition, it was reported that more than 60% of athletes who sustained a stress fracture over a 12-month period had sustained a prior fracture on one or more occasions.17 A range between 8 and 17 weeks has been reported from the time of diagnosis to a return in full activity resumption, and this has been reported to vary according to injury site.9

 

Similarly, the characteristics of training regimens are correlated with stress fracture occurrence. Lauder et al. reported that women runners who sustained stress fractures incurred significantly higher weekly exercise intensity (428 minutes [7.1 hours] versus 292 minutes [4.9 hours] minutes per week) than those without fractures (P < 0.05).18 This contrast was apparent when exercise intensity was stratified according to weekly mileage, particularly when one ran over 10 miles/week (less than 5 miles per week-11.7% rate of stress fracture; 5 to 10 miles per week-14.6% rate of stress fracture; over 10 miles per week-50.0% rate of stress fracture). It also has been noted that ballet dancers who work out for 6 hours a day or more have a higher risk of stress fractures than ballet dancers who train for less.4

 

Age

Age has not definitively been determined to be a risk factor for stress fractures. This lack of clear correlation is due to conflicting results across studies as well as variable activity intensity for different age groups. Some studies do correlate increasing age with a higher incidence of stress fractures, suggesting that aging bone may be less resistant to fatigue failure.19

 

Gender

Women have been identified as having a higher incidence of stress fractures than men. This may be associated with gender-related risks such as narrower bone width, decreased BMD, menstrual irregularities, and dietary deficiencies. In military recruits the difference in the incidence of stress fractures in women may be as much as tenfold higher than in men.4,9

 

Race/ethnicity

Several studies have demonstrated a significantly higher incidence of stress fractures in Asian women and White women as compared to Black women. It is believed that this disparity is related to variances in peak bone density as well as bone turnover differences.4

 

Bone mineral density

Myburgh et al. were among the first to identify an inverse relationship between BMD and stress fractures in the femoral neck (P = 0.005).20 Lauder et al. examined this relationship in women military recruits.18 In that study, multivariate analyses determined an inverse relationship between femoral neck BMD and the likelihood of sustaining a stress fracture (P < 0.05). This correlation has been seen particularly in cancellous bones. Marx et al. identified that 89% of women who sustained stress fractures of the calcaneus, sacrum, medial femoral neck, and pubic rami had osteopenia in either the femoral shaft or lumbar spine.21 This compared with 27% of those in the same cohort who had a cortical stress fracture. This suggests that exercise regimens should balance the positive effect of increased exercise (increases BMD) with the unfavorable effect of BMD on the development of stress fractures.

 

In athletes who are runners, significant differences have been noted in BMD when compared to nonexercising controls, particularly in the distal bones of the lower limb (P < 0.05), suggesting that there may be a localized effect of mechanical loading on bone formation.22

 

Nutritional factors

Several nutritional factors may contribute to stress fractures. Low calcium intake is associated with low BMD, and may be a contributing factor. The results of studies are mixed at this point. Vitamin D is central to bone health, and it is correlated with stimulating osteoblasts, calcium transport stimulation, and reducing parathyroid hormone. One clinical trial has reported that 500 mg/day calcium supplementation had no effect on the incidence of stress fractures in male military trainees.23 However, restrictive eating habits may increase the risk of stress fracture in women.17

 

Disordered eating is one component of the female athlete triad, which also includes osteoporosis, and amenorrhea, and is potentially lethal.4 This syndrome is correlated with stress fractures. More studies need to be conducted regarding these relationships.

 

Diagnostic considerations

Stress-related injuries occur on a continuum, ranging from less severe stress reactions to more severe injuries that are termed stress fractures. These injuries on this continuum are caused by repetitive loading and resultant bone stress. Depending on the affected site, most persons who sustain a stress reaction or stress fracture present with a clinical history of progressive pain with an insidious onset in a specific area. Initially, this may be present only with activity, and the person may associate it with muscle soreness. As the process continues to develop, the pain becomes worse and begins to interfere with activity, performance, and activities of daily living. Pain may be continuous at a certain point.

 

Radiographic imaging can be used to supplement clinical history and to guide treatment. Radiography has a low sensitivity for stress fracture, especially during the first two symptomatic weeks. Films may exhibit slight periosteal bone formation, osteopenia, a poorly defined cortical margin, and in severe cases, a fracture line. MRI is becoming the gold standard for this type of injury, in large part because of its ability to visualize both soft tissue and bony edema.7 In addition, it is sensitive to bone marrow edema, one of the earliest signs of stress fracture.7 It provides a breadth of information to the clinician, and shows the precise location and extent of the injury (see Navicular stress fracture on MRI).

 

The severity of a fracture on an MRI is classified according to one of four grades. This grading system was initially developed for tibial stress fractures but can be used for any stress fracture, and is classified numerically as follows: (0) normal; (1) mild-to-moderate periosteal edema, without any abnormal bone marrow; (2) more severe periosteal edema in addition to bone marrow edema; (3) moderate-to-severe edema of both periosteum and bone marrow; (4) low signal fracture line with severe marrow edema, and may display moderate muscle edema and severe periosteal edema.10A study conducted with symptomatic athletes classified their injuries as follows: grade 0-11%, grade 1-11%, grade 2-16.7%, grade 3-55.5%, and grade 4-5.6%.10 In addition, significant differences in the time span between a diagnosis and return to activity have been noted according to fracture grade.12 The time to recovery ranged from 3.3 weeks for grade 1 injuries to an upper range of 14.3 weeks for those injuries classified as grade 4.12 Bones that have sustained a grade 1 or grade 2 stress fracture are generally able to heal in the face of continued stress. In addition, up to 90% of stress fractures in the foot have been found to be a grade 3 or 4 at time of diagnosis, suggesting that many of these fractures may not be diagnosed in a timely fashion.9

 

Although the large majority of stress fractures heal with conservative treatment with an average return to activity in approximately 8 weeks, there have been reports of a small number that have required surgical intervention due to delayed union or progression to nonunion.9

 

In order to resolve these fractures, abstaining from running is necessary for a period of time. There is no "one-size-fits-all" approach to recovery. Many providers recommend crutches and non-weight bearing on the affected side for a variable period of weeks. Pain should be treated appropriately. Activity should always be free from pain, and if pain does recur upon activity, that activity should cease for several days and then resume at a less strenuous level. Prior to resuming running again, the runner should be free from pain when participating in activities of daily living for a period of several weeks. Runners can maintain cardiovascular fitness during this period by participating in non-weight-bearing activities such as swimming or cycling. These keep large muscle groups in shape without straining the bones. A shortened return to full activity has been demonstrated for some stress fractures that occur in the lower limb when braces are utilized.19

 

Menstrual irregularities such as amenorrhea (less than three menstrual cycles per year) can occur, particularly in very lean women who compete at high levels. This increases stress fracture risk.17 It has been suggested that the primary reason for bone loss with this type of amenorrhea is due to dietary constraint/excessive exercise, with a resultant low availability of energy. This relative lack of energy suppresses bone remodeling and bone formation.24

 

Low-risk stress fractures

Stress fractures can be classified as either low- or high-risk. Common locations for low-risk stress fractures include the shaft of the femur, sacrum, pelvis pubic ramus, fibula, tibia, and metatarsal shaft. Most of these types of fractures heal without incident with activity modification and a period of rest.

 

Shaft of the femur: A very small percentage of stress fractures occur in the shaft of the femur, and this type of fracture can be underdiagnosed. The posteromedial and mid-medial cortex are most commonly affected, and usually occur due to repetitive compressive force. People often experience nonspecific pain that can be located in the knee, groin, or thigh. Due to the relatively large protective muscle mass in the thigh, physical exam often does not add pertinent diagnostic information. Most often, this type of injury is treated quite conservatively, return to previous level of activity is accomplished very gradually, and degree of recovery is correlated with pain that occurs with weight bearing and varying levels of activity.25,26

  
Figure. Navicular st... - Click to enlarge in new windowFigure. Navicular stress fracture on MRI

Sacrum: The true incidence of sacral stress fractures is not known, but it can mimic other back/gluteal pain-related conditions. Most of the time, patients complain of lower back pain or pain in the buttocks. Radiographs usually do not assist in making the diagnosis. Treatment usually involves up to 8 weeks of resting. This is followed by a gradual return to preinjury level of activity as long as pain does not recur. Progressive rehabilitative programs for this injury include rest for the first 2 weeks; increasing activity including up to 90 minutes of cycling and moderate cross-training; between 60 and 90 minutes of daily walking plus twice weekly moderate strength training and Nordic pole walking for 2 weeks; resuming running at 7 weeks postinjury with a gradual increase to 55 miles/week.27

 

Pelvis/pubic ramus: Approximately 1% to 7% of all stress fractures occur in the pelvis, and the most common location is the inferior pubic ramus. The presenting symptoms (groin pain) can mimic an adductor muscle strain. These fractures can require extended periods of rest, so an early and accurate diagnosis is essential to treatment.26

 

Fibula: Fibula fractures represent between 4% and 21% of stress fractures, and usually arise in the distal third portion of the bone. Since the fibula plays less of a role in weight-bearing mechanics, the causative factors of these stress fractures are thought to be related to muscles. Most frequently, there is a history of marked increase in intensity of exercise along with pain at the fracture site. Radiographs may initially be negative, and thus MRI or bone scan should then be used to correctly diagnose. Treatment usually includes a period of rest followed by gradual increase in activity, similar to treatment for other low-risk stress fractures.26

 

Tibia: The tibia is the larger and stronger bone of the lower leg, and is the second largest bone in the human body. Approximately 50% of stress fractures are located in the tibia, making this the most common site of stress fractures in athletes.26 Most of the time, these fractures occur in the middle third of the shaft, in the posteromedial aspect of the bone. Any runner who experiences shin pain exacerbated by exercise and bearing weight should be evaluated for a stress fracture in this bone. Radiographs are frequently negative, and an MRI or bone scan may be required to correctly diagnose. Treatment and a return to preinjury levels of activity are usually developed on an individual basis, and are guided by an increase of the level of activity only when activity is pain-free. Bracing is frequently utilized as part of the treatment regimen. A return to preinjury levels of activity takes several months. Frequently, the initial period of resting the bone continues for several weeks, followed by a gradual increase in intensity and amount of activity.26

 

Metatarsal shaft: Stress fractures in metatarsal bones represent approximately 10% of athletic stress fractures.26 These fractures are also referred to as "march fractures," and usually occur with a marked increase in intensity or level of activity. Metatarsal fractures most commonly occur in the shaft of the second or third metatarsal.26 Patients frequently present with pain upon activity, which may or may not be localized in nature. A negative radiograph is common, and MRI and bone scan can then be done in order to assist with the diagnosis. Treatment includes a prefabricated walking boot or short-leg cast for several weeks, with progressive weight bearing. A gradual increase in intensity and level of activity follows.26

 

High-risk stress fractures

High-risk stress fractures are those that are at risk for nonunion or delayed healing for various reasons, and include the proximal fifth metatarsal, anterior tibia, medial malleolus, femoral neck, navicular, and sesamoid.

 

Proximal fifth metatarsal: Stress fractures in this location represent less than 10% of stress fractures. This type of fracture is at risk for nonunion and delayed healing (between 20% and 67% risk), making this a high-risk injury.28 Typically, people report gradual worsening of pain, particularly after activity. Ecchymosis, edema, and tenderness on palpation may be present. Radiographs frequently are used to make the diagnosis, but at times a diagnosis can only be made with utilization of MRI or bone scan. Conservative treatment may result in healing (6 to 8 weeks non-weight bearing in a cast followed by progressive rehabilitation). The presence of continued symptoms despite conservative treatment should result in a surgical consultation.7,28,29

 

Anterior tibia: In athletes, tibial fractures account for almost half of all stress fractures, and should be considered in any runner presenting with anterior leg pain. Fifty percent of tibial fractures are posteromedial and are considered to be low risk.30 When a fracture occurs on the tension side of the bone, it is at higher risk for nonunion of the bone and delayed healing. Usually, the emergence of pain is correlated with a marked increase in intensity or level of activity. The runner may experience swelling, a callus that is palpable, or tenderness on palpation. Pain may persist at rest and with ambulation. Radiograph images may be negative, and MRI may need to be done in order to make a definitive diagnosis. Treatment frequently involves surgical intramedullary nailing, since conservative treatment may fail. It has been reported that surgical intervention leads to much earlier returns to prior levels of activity (4 months) as opposed to conservative treatment (8 months).31 Pneumatic braces have also been utilized for this type of injury.7,30

 

Medial malleolus: Stress fractures of the medial malleolus represent less than 5% of athletic stress fractures, and can occur in runners.32 Gradually worsening pain that begins after an increase in intensity or activity is typical. This pain is usually localized to the medial malleolus area. These fractures are vertical in nature, occur at the junction of the tibial plafond and medial malleolus, and extend proximally. Upon palpation of the area, tenderness is usually elicited. Radiograph images may be negative for several weeks. MRI may be utilized in order to make the proper diagnosis. Treatment is usually conservative, with a pneumatic brace in place in order to stabilize the area. If the fracture is displaced, open reduction and internal fixation is recommended.7,32

 

Femoral neck: While stress fractures in the femoral neck represent approximately 5% of all stress fractures, they represent an extremely significant injury in runners, and represent 50% of all femoral stress fractures.33 The neck of the femur withstands forces that represent loads higher than body weight. In addition, it withstands high compression and tensile force levels. Typically, runners will present with groin or anterior hip pain that is exacerbated with activity or exercise. The pain is usually correlated with an increase in exercise intensity. Frequently, radiography does not reveal the fracture during the early weeks. This can present a problem, especially given that this type of fracture can be at risk for nonunion and displacement. It has been reported that up to 60% of those with a displaced femoral neck fracture who were appropriately treated were unable to return to their prior level of exercise.7 MRI should be done in order to correctly make a diagnosis and to rule out other causes of pain in this area. Femoral neck stress fractures have complication rates as high as 30%, including delayed union, osteonecrosis, and nonunion.33 These fractures usually are treated with rest, progressing to a gradual return to previous levels of activity and exercise. A return to running is only considered when the person is pain-free when full weight-bearing, and no tenderness is present on palpation. In addition, follow-up imaging should be done to determine progression to healing. Some of these fractures can be at risk for sustaining complications, and thus many recommend that internal fixation be utilized for this type of tension-related injury.25

 

Navicular: Approximately 30% of stress fractures occur in the navicular bone.34 This type of fracture is more common in men than it is in women, and more typically associated with sprinters, hurdlers, and mid-distance runners (versus long distance runners). The center of this bone has relatively less blood supply than the rest of the bone, thus rendering it more vulnerable to poor healing. The typical history involves increasing pain in the midfoot after activity, often exacerbated by specific activities (for example, jumping). A recent increase in intensity or activity is reported, and the area over the bone may be tender to palpation, especially in the dorsal area. Radiographic imaging may be normal, and bone scan, CT scan, or MRI may be needed in order to make the proper diagnosis. Due to the bone's vulnerability, the fracture is usually treated with a non-weight-bearing cast until healing takes place. After the cast is removed, gradual resumption of weight bearing occurs, with the presence of pain guiding level of activity. The length of rehabilitation may be up to 8 months duration until full activity can be resumed. Some of these fractures that extend into the navicular body and the opposite cortex require surgical intervention.7,34

 

Sesamoids: Sesamoid bones are located in the knee, hand, and foot. The sesamoid(s) located in the foot are susceptible to stress fractures. Patients usually present with a gradual increase in pain with activity. Tenderness upon palpation may be present. Initial radiographs are often negative for the first few weeks. With a high level of suspicion, a bone scan or MRI should be performed. These stress fractures are at high risk for osteonecrosis, sesamoiditis, nonunion, or delayed union. As a result, an extended time period of casting or non-weight bearing is recommended. If conservative treatment does not result in abatement of symptoms, sesamoidectomy is usually considered.7,35

 

Prevention of stress fractures

Persons who have sustained a stress fracture have a higher risk of future stress fractures. In addition to healing the bone, successful stress fracture treatment should focus on reasons why the injury occurred as well as preventing future stress fractures. There are several recommendations that may lend themselves to the prevention of stress fractures in runners.

 

Training surface

Softer surfaces such as a treadmill (as opposed to an asphalt road) can decrease limb stress, as can the scheduling of rest days after higher intensity runs. When running on a cambered surface such as an asphalt road, the runner should run on alternating sides of the road.

 

Footwear

It has been recommended that runners limit the amount of miles they cumulatively accrue in a given pair of running shoes to 300 to 500 logged miles. In addition, foot orthoses that absorb shock have been shown to decrease stress fracture risk by 50% in military recruits, and have been recommended by a Cochrane review.36 However, it has not been demonstrated that this finding can be generalized to all those who run, who wear varying footwear and implement different training. Individualized plans can and should be developed with runners, depending on their risks, severity, and location of injury.

 

Speed

When running speed is reduced, the numbers of loading cycles increase for a given amount of mileage covered (assuming that a decrease in speed is correlated with a decrease in stride length). Edwards et al. studied the relationship between running speed and incidence of stress fracture.25 They determined that a decrease in speed from 4.5 to 3.5 m/second reduced stress fracture probability by 7% (P = 0.017), and a reduction in speed from 3.5 to 2.5 m/second further reduced stress fracture probability by 10% (P < 0.001). This suggests that a decrease in speed may reduce the risk of stress fracture in runners.

 

Training regimens

There is some evidence that muscle fatigue may increase the risk of stress fractures. Therefore, many providers recommend systematic muscle strengthening programs (especially for calf muscles) as well as muscle recovery interventions between workout sessions (for example, massage, icing). Similarly, there is some evidence that increasing mileage correlates with increase in stress fractures; therefore, what is appropriate for some may be too much for others. Increasing training regimens gradually to a new level and then keeping that level steady for several weeks may help bone adapt to the new load.4

 

Some coaches maximize performance gains and reduce injury risks by developing a 4-week training cycle that includes 3 weeks of progressive training followed by 1 week of less intensive training.7 In 2010, the Joint Physical Training Injury Prevention Working Group recommended that training days should be alternated between upper body conditioning and lower body-weight bearing activities.37

 

Muscle endurance is also particularly important to develop. Runners may want to consider keeping a log that details volume, type, frequency, and intensity of activity so that the appropriate training levels can be determined.19 It has been suggested that a gradual increase in intensity of activity be initiated after healing a stress fracture, and includes cycling, followed by walking/leg press/stepper machine then adding running on a treadmill, and progressing to straight line running, sprinting, curved track, up and down hills, jumping, and then hopping.

 

For stress fractures related to running, the following type of plan to build up strength and endurance while minimizing bone stress may also be reasonable: brisk walking that is increased 5 to 10 minutes a day to the level of 45 minutes a day. Once the 45 minutes is endured pain-free, one can initiate slow jogging for 5 minutes when walking for those 45 minutes. One can increase this substitution of jogging for walking by 5 minutes per session (daily or every other day) to a buildup to 45 minutes of slow jogging. Once that level is achieved, one can increase the pace (half pace progressing to full pace) slowly. This should be a very gradual process, and if bone pain is felt, activity level should be ceased for several days, and if free from pain, resume activity at a level below that which precipitated the pain. One may want to favor treadmill jogging over use of a road surface due to the difference in hardness of surface. The person should be reevaluated every 2 weeks in order to closely monitor and oversee progress.19

 

Ivkovic et al. tested a specific treatment algorithm with athletes who had sustained a stress fracture of the femoral shaft.38 They followed a cohort of seven athletes for 48 to 96 months. There was no recurrence of pain or fracture(s), and all the athletes were able to return to sports competition levels of activity. All were fully engaged in athletic exercise within 12 to 18 weeks following the initiation of treatment. The four phases were delineated as follows, each lasting 3 weeks. At the end of each phase, if the patient was unable to hop on the affected leg ("hop test") or sustain fulcrum pressure ("fulcrum test") to the affected leg, they were returned to the beginning of that phase, and only progressing to the next phase when successfully passing the aforementioned tests at the end of each phase:

 

1. "Symptomatic Phase"-walk non-weight bearing on the affected leg with crutches

 

2. "Asymptomatic Phase"-normal walking; begin swimming in the pool, and exercising upper extremities and unaffected leg in the gym

 

3. "Basic Phase"-upper and lower extremity exercises, use smaller weights, run in a straight line every other day, ride stationary bicycle. Running distance gradually increases

 

4. "Resuming Phase"-gradual resumption of normal training.

 

 

Nutrition

In 2010, the Joint Physical Training Injury Prevention Working Group recommended the consumption of 50 to 75 g of carbohydrates, a fluid replacement beverage, and 12 to 18 g of protein (a ratio of 4 g of carbohydrate to 1 g of protein) within 1 hour of strenuous activity that lasts an hour or longer. This regimen was found to maximize musculoskeletal recovery from breakdown precipitated by the activity as well as restoration of energy. This window period allows for optimal rebuilding, whereas when the nutrients are consumed outside this window period, there is less ability to absorb the nutrients, thereby diminishing musculoskeletal recovery.37

 

Role of the advanced practice nurse

Advanced practice nurses are assuming a growing role in providing healthcare in the United States. They come in contact with a broad array of clinical presentations in the course of providing health care. In order to appropriately manage patients' health, advanced practice nurses must be alert for those who may present with the requisite history and symptoms that may be indicative of a possible stress fracture. These symptoms may be subtle and insidious, and should be appropriately assessed through the utilization of several diagnostic tools. Appropriate management depends on the type and severity of a stress fracture, and should be individually tailored.

 

Minimizing risk is key

Stress-related injuries are not uncommon in athletes, particularly in runners. They result from repetitive loading and the bones' adaptation to these changes. There are certain modifiable risks associated with the development of these injuries. The locations can vary. Recovery can be variable and can depend on location as well as other preexisting risk factors. Once a stress fracture occurs, a person is at high risk for recurrence. Thus, it is the responsibility of the clinician to work with the patient and individualize a plan in order to minimize the risk of recurrence.

 

REFERENCES

 

1. Centers for Disease Control and Prevention. How much physical activity do adults need? 2011. http://www.cdc.gov/physicalactivity/everyone/guidelines/adults.html. [Context Link]

 

2. Carlson SA, Fulton JE, Schoenborn CA, Loustalot F.Trend and prevalence estimates based on the 2008 physical activity guidelines for Americans. Am J Prev Med. 2010;39(4):305-313. [Context Link]

 

3. United States Bureau of Labor Statistics. Sports and exercise. 2008. http://www.bls.gov/spotlight/2008/sports/. [Context Link]

 

4. Pepper M, Akuthota V, McCarty EC.The pathophysiology of stress fractures. Clin Sports Med. 2006;25(1):1-16. [Context Link]

 

5. Matsuo K, Irie N.Osteoclast-osteoblast communication. Arch Biochem Biophys. 2008;473(2):201-209. [Context Link]

 

6. Chapurlat RD, Delmas PD.Bone microdamage: a clinical perspective. Osteoporosis Int. 2009;20(8):1299-1308. [Context Link]

 

7. Boden BP, Osbahr DC.High-risk stress fractures: evaluation and treatment. J Am Acad Orthop Surg. 2000;8(6):344-353. [Context Link]

 

8. Athanasou NA.Pathology of bone injury. Diagn Histopathol. 2009;15(9):437-443. [Context Link]

 

9. Snyder RA, Koester MC, Dunn WR.Epidemiology of stress fractures. Clin Sports Med. 2005;25(1):37-52. [Context Link]

 

10. Fredericson M, Bergman AG, Hoffman KL, Dillingham MS.Tibial stress reaction in runners: correlation of clinical symptoms and scintigraphy with new magnetic resonance imaging grading system. Am J Sports Med. 1995;23(4):472-481. [Context Link]

 

11. Koh JS, Goh SK, Png MA, Ng AC, Howe TS.Distribution of atypical fractures and cortical stress lesions in the femur: implications on pathophysiology. Singapore Med J. 2011;52(2):77-80. [Context Link]

 

12. Arendt E, Agel J, Heikes C, Griffiths H.Stress injuries to bone in college athletes: a retrospective review of experience at a single institution. Am J Sports Med. 2003;31(6):959-968. [Context Link]

 

13. Bennell KL, Brukner PD.Epidemiology and site specificity of stress fractures. Clin Sports Med. 1997;16(2):179-196. [Context Link]

 

14. Gottschall JS, Kram R.Ground reaction forces during downhill and uphill running. J Biomech. 2005;38(3):445-452. [Context Link]

 

15. O'Connor KM, Hamill J.Does running on a cambered road predispose a runner to injury. J Appl Biomech. 2002;18(1):3-14.

 

16. Gehlsen GM, Stewart LB, Van Nelson C, Bratz JS.Knee kinematics: the effects of running on cambers. Med Sci Sports Exer. 1989;21(4):463-466. [Context Link]

 

17. Bennell KL, Malcolm SA, Thomas SA, Wark JD, Brukner PD.The incidence and distribution of stress fractures in competitive track and field athletes: a twelve-month prospective study. Am J Sports Med. 1996;24(2):211-217. [Context Link]

 

18. Lauder TD, Dixit S, Pezzin LE, Williams MV, Campbell CS, Davis GD.The relation between stress fractures and bone mineral density: evidence from active-duty army women. Arch Phys Med Rehabil. 2000;81(1):73-79. [Context Link]

 

19. Bennell KL, Brukner PD.Preventing and managing stress fractures in athletes. Phys Ther Sports. 2005;6(4):171-180. [Context Link]

 

20. Myburgh KH, Hutchins J, Fataar AB, Hough SF, Noakes TD.Low bone density is an etiologic factor for stress fractures in athletes. Ann Intern Med. 1990;113(10):754-759. [Context Link]

 

21. Marx RG, Saint-Phard D, Callahan LR, Chu J, Hannafin JA.Stress fracture sites related to underlying bone health in athletic females. Clin J Sports Med. 2001;11(2):73-76. [Context Link]

 

22. Bennell KL, Malcolm SA, Khan KM, et al.Bone mass and bone turnover in power athletes, endurance athletes, and controls: a 12-month longitudinal study. Bone. 1997;20(5):477-484. [Context Link]

 

23. Schwellnus MP, Jordaan G.Does calcium supplementation prevent bone stress injuries? A clinical trial. Int J Sport Nutr. 1992;2(2):165-174. [Context Link]

 

24. Pollock N., Grogan C., Perry M., Pedlar C., et al.Bone-mineral density and other features of the female athlete triad in elite endurance runners: a longitudinal and cross-sectional observational study. International Journal of Sport Nutrition and Exercise Metabolism. 2010;20:418-426. [Context Link]

 

25. Edwards WB, Gillette JC, Thomas JM, Derrick TR.Internal femoral forces and movements during running: implications for stress fracture development. Clin Biomech. 2010;23(10):1269-1278. [Context Link]

 

26. Fredericson M, Jennings F, Beaulieu C, Matheson GO.Stress fractures in athletes. Top Magn Reson Imaging. 2006;17(5):309-325. [Context Link]

 

27. Knobloch K, Schreibmueller L, Jagodzinski M, Zeichen J, Krettek C.Rapid rehabilitation programme following sacral stress fracture in a long-distance running female athlete. Arch Orthop Trauma Surg. 2007;127(9):809-813. [Context Link]

 

28. Saxena A, Liu GT, Fullem BW, Allen MA.Stress fractures of the foot and ankle in athletes. In: Saxena, A.L. International Advances in Foot and Ankle Surgery. London: Springer; 2012: 235-251. [Context Link]

 

29. Dameron TB.Fractures of the proximal fifth metatarsal: selecting the best treatment option. J Am Acad Orthop Surg. 1995;3(2):110-114. [Context Link]

 

30. Shindle MK, Endo Y, Warren RF, Lane JM, et al.Stress fractures about the tibia, foot, and ankle. Journal of the American Academy of Orthopaedic Surgeons. 2012. 20, 167-176. [Context Link]

 

31. Stewart GW, Brunet ME, Manning MR, Davis FA.Treatment of stress fractures in athletes with intravenous pamidronate. Clin J Sport Med. 2005;15(2):92-94. [Context Link]

 

32. Kor A, Saltzman AT, Wempe PD.Medial malleolar stress fractures: literature review, diagnosis, and treatment. J Am Podiatr Med Assoc. 2003;93(4):292-297. [Context Link]

 

33. Lee CH, Huang GS, Chao KH, Jean JL, Wu SS.Surgical treatment of displaced stress fractures of the femoral neck in military recruits: a report of 42 cases. Arch Orthop Trauma Surg. 2003;123(10):527-533. [Context Link]

 

34. Mann JA, Pedowitz DI.Evaluation and treatment of navicular stress fractures, including nonunions, revision surgery, and persistent pain after treatment. Foot Ankle Clin. 2009;14(2):187-204. [Context Link]

 

35. Saxena A, Krisdakumtorn T.Return to activity after sesamoidectomy in athletically active individuals. Foot Ankle Int. 2003;24(5):415-419. [Context Link]

 

36. Rome K, Handoll HHG, Ashford RL.Interventions for preventing and treating stress fractures and stress reactions of bone of the lower limbs in young adults (Cochrane Review). In: The Cochrane Library. Issue 2. Oxford: Update Software; 2005. [Context Link]

 

37. Bullock SH, Jones BH, Gilchrist J, Marshall SW.Prevention of physical training-related activities: recommendations for the military and other active populations based on expedited systemic reviews. Am J Prev Med. 2010;38(1 suppl):S156-S181. [Context Link]

 

38. Ivkovic A, Bojanic I, Pecina M.Stress fractures of the femoral shaft in athletes: a new treatment algorithm. Br J Sports Med. 2006;40(6):518-520. [Context Link]