Female participation in athletic activities has grown enormously over the past quarter century. The passage of Title IX in 1972 has dramatically increased the number of young women participating in organized sports. In addition, women are now frequently involved in recreational athletic activities, constituting over 40% of all runners. 1 This increased participation has resulted in an increased incidence of overuse athletic injuries. The medical community has responded with a heightened interest in the diagnosis, treatment, and prevention of female athletic injuries.
Stress fractures are common overuse injuries seen in both female and male athletes. These injuries affect athletes in a wide variety of sporting activities. The majority of stress fractures resolve with simple, nonoperative treatment. However, an athlete with a stress fracture can lose significant time away from their sport. In rare cases, these injuries can be more serious and require surgical intervention that may threaten the athlete's career. Although the etiology, diagnosis, and treatment of stress fractures are similar in female and male athletes, there are unique issues that affect the female athlete.
Breithaupt 2 first noted the clinical entity of swollen, painful feet in military personnel, which was termed a march fracture. There have been a number of subsequent reports of stress fractures in military personnel and athletes. Unfortunately, most of these studies are limited to case reports and retrospective reviews.
Stress fractures most commonly affect the lower extremity; the tibia is the site most commonly affected in both female and male athletes. 3–5 Recent studies of athletes have shown a higher incidence of stress injuries of the tarsal bones and femoral shaft than previously appreciated. 5,6 Female athletes sustain stress fractures of the femoral neck, metatarsals, and pelvis more frequently than their male counterparts. 3,5,6
Stress fractures are seen most commonly in runners, but they have been reported in athletes from a variety of athletic activities. 5 Bennell et al. 3 reported a 20% incidence of stress fractures in a prospective study of competitive track and field athletes, while others have reported a 13% incidence of stress fractures in a large study of recreational runners. 4 Johnson et al. 6 prospectively studied a group of collegiate athletes and found the highest incidence of stress fractures in track athletes (9.7%), followed by lacrosse athletes (4.3%) and crew athletes(2.4%).
Certain stress fractures are associated with specific sports. Stress fractures of the tibia, fibula, and tarsals are common in runners, soccer players, and ballet dancers. 2,3,7 Throwers develop stress fractures of the humerus and olecranon, whereas those participating in racquet sports sustain stress fractures to the ulna and metacarpals. Rib stress fractures have been reported in rowers. Fibular and medial malleolar fractures are seen in figure skaters, whereas gymnasts sustain fractures to pars interarticularis and the upper extremity. 2,7,8
Women sustain stress fractures more frequently than men. This increased incidence in women has been shown in a number of studies involving military recruits, in which female recruits had up to a 10-fold higher incidence of stress fractures than male recruits. 7,9,10 This is partially a result of a lower level of initial physical fitness in female recruits.
The difference in the stress fracture rate between women and men in an athletic population may not be as dramatic. There was no significant difference in the incidence of stress fractures between male and female track and field athletes, as reported by Bennell et al. 3 Other investigators have reported a nearly four-fold increase in the incidence of stress fractures in women, in a prospective study of collegiate athletes. 6 Experience at the United States Military Academy has consistently shown a five-fold greater risk of stress fractures in female cadets in recent years. 11 The female cadets more closely represent an athletic population, since nearly 45% of women participate in intercollegiate athletics, and all female cadets participate in year-round, high-level physical activity. Female athletes are at greater risk for stress fractures, but the difference between women and men is smaller in the well-trained athlete.
PATHOPHYSIOLOGY AND RISK FACTORS
Bone is a dynamic tissue that responds to external forces with adaptive remodeling that involves new bone formation as well as bone resorption. Stress-induced injury to bone occurs when the loads placed on the bone exceeds its capacity for repair. This is best viewed as a continuum from physiologic remodeling, progressing to microarchitectural damage (stress reaction), and then true cortical disruption (stress fracture). 12 The exact pathogenesis of stress fractures is unclear, but most likely involves a complex interaction of mechanical, hormonal, nutritional, and genetic factors. 13 This interaction is seen in its extreme form in the recently described female athlete triad, which involves disordered eating, amenorrhea, and osteoporosis. 14
Disordered eating and the female athlete triad have received considerable attention recently. The prevalence of disordered eating among female athletes may range from 4% to 62%, but the true number is unknown because of the secretive nature of eating disorders. 15 Disordered eating is seen most commonly in female athletes competing in sports where appearance is felt to be an important contributor to the athlete's success. This includes gymnastics, figure skating, and ballet. In addition, many female athletes and coaches in other sports believe that being thinner enhances performance. Some athletes will meet the criteria for anorexia nervosa or bulimia, but many athletes will have a body weight that is near normal. These athletes will still exhibit many characteristics of disordered eating, and the American Psychiatric Association has established a new diagnosis, called eating disorder not otherwise specified, to assist in diagnosing these patients. 15,16
Osteoporosis and decreased bone mineral density (BMD) have been implicated in the development of stress fractures in female athletes. Decreased BMD may be part of the female athlete triad, or may be seen in women without a diagnosed eating disorder. Although it seems intuitive that decreased BMD would be an important risk factor for stress fractures, the relationship is not clearly defined. Some investigators have shown that decreased BMD is a risk factor for stress fractures in female military recruits and athletes. 17,18 Conversely, reports by Carbon et al. 19 and Bennell et al. 20 found no correlation between BMD and stress fractures in élite female athletes. Bone mineral density most likely plays a role in the pathogenesis of stress fractures, but the relationship is complex and involves other variables.
Hormonal balance is an important component for bone health in women. The proper amount of estrogen is necessary for women to obtain maximum peak bone mass during the second and third decades. Female athletes who are amenorrheic or oligomenorrheic will lose bone mass instead of adding bone during these crucial years, and this bone loss may be permanent. 21 Menstrual abnormalities can lead to decreased BMD, but not all amenorrheic women will have lower BMD. In addition, amenorrheic women with healthy BMD still have an increased incidence of stress fractures, so amenorrhea may be an independent variable in the development of stress fractures. 7,21 Finally, there does seem to be a close relationship between eating disorders and amenorrhea, because the incidence of eating disorders is considerably lower in the regularly menstruating athlete.
Other risk factors that may predispose women to stress fractures include smaller bone size and less muscle mass. A narrow tibia has been implicated as a risk factor for stress fractures, and because women have a smaller skeleton, this may play a role in the development of stress fractures in the female athlete. 22 Muscle fatigue has also been implicated in the development of stress fractures, because of the decreased load dissipation associated with fatigued muscle. 23 Earlier muscle fatigue and an increased risk of stress fractures occur in female athletes because of lower overall muscle mass. However, there are no studies that independently look at these variables in female athletes.
The most important risk factors in the development of stress fractures are independent of the athlete's gender. Training errors are the most important predisposing factors in the development of stress fractures in both female and male athletes. High mileage, high intensity, or an abrupt change in the training program are common errors that result in stress fractures. 4,10,24,25 Other training errors that may increase the risk of stress fractures include training on uneven surfaces or using worn running shoes, although the cost of the running shoe does not seem to correlate with stress fracture risk. 26,27 Other reported risk factors that are not related to gender include limb length discrepancy, a high longitudinal arch, and foot pronation. 5,24
In summary, the pathogenesis of stress fractures is multifactorial. Further controlled studies are required to clearly elucidate which predisposing factors play the most important role in the development of stress fractures. Defining the key risk factors will give coaches, trainers, and clinicians the opportunity to intervene prior to injury.
The diagnosis of stress fractures should be made in a timely fashion. Prompt treatment will allow athletes to return to their sport in the shortest time. More importantly, disastrous complications, such as displacement of a femoral neck fracture or collapse of a tarsal navicular fracture, can be avoided. Most stress fractures can be diagnosed with a thorough history and physical examination, along with confirmatory imaging studies.
The athlete with a stress fracture usually presents with gradual onset of activity-related pain. The pain is frequently described as an ache that resolves with rest. The symptoms will progress if the athlete continues with activities, eventually interfering with the ability to perform impact-loading activities. In more severe cases, walking will be painful, and pain may be present at rest. Occasionally, the athlete may present with an acute increase in pain, consistent with fracture propagation or displacement.
A careful history regarding the athlete's training pattern is important. Changes in the intensity or duration of training should be noted, as well as changes in training surface or shoes. Previous history of stress fracture should be noted, as well as a history of other overuse injuries. Nutritional history should be obtained, with a high index of suspicion for eating disorders. Information regarding the menstrual history must be noted, including age at menarche and current menstrual status. The athlete's goals and upcoming competitions should be ascertained. 28
Athletes with lower extremity stress fractures will often walk with an antalgic gait. Focal tenderness, swelling, and erythema are frequently present when the fracture involves the more bones of the leg and foot. Johnson et al. 6 have described a fulcrum test to aid in the diagnosis of femoral shaft stress fractures. The examiner places her or his arm under the thigh and applies pressure to the dorsum of the knee, with the athlete sitting on the edge of an examination table. The arm is moved proximal to distal to test the entire femur. A sharp pain indicates the likely possibility of a femoral shaft stress fracture. Decreased range of motion of the hip, and pain with maximum internal rotation, are often present in femoral neck stress fractures. In addition, the heeltap or hop test may be positive in femoral neck or pelvis stress fractures.
The physical examination should also note predisposing anatomic factors. Limb length discrepancy, muscle mass, foot alignment, and flexibility should be recorded. 28
The clinician can make the diagnosis of stress fracture, in most cases, from the history and physical examination. However, confirmatory imaging studies are frequently obtained in most athletes, to help guide treatment and training recommendations.
Radiographs are usually obtained as the initial diagnostic study. Findings typical of stress fractures include periosteal bone reaction, cortical lucency, callus formation, or a fracture line. 28 Radiographs may be completely normal for the first few weeks after the onset of symptoms, and in some cases, the radiographs may remain normal for several months. 29 Some clinicians report that only 50% of stress fractures will ever be evident on plain radiographs. 2
The technetium-99 diphosphonate bone scan is nearly 100% sensitive in diagnosing stress fractures. 30 Bone scan changes are present within 48 to 72 hours after the onset of symptoms (Fig. 1A), but bone scans have poor specificity. Specificity is improved with the three-phase bone scan: medial tibial periostitis will be positive on the delayed phase only, while stress fractures are positive in all three phases. However, it is still difficult to locate the precise fracture site in the foot using this imaging technique. In addition, other bony lesions, such as tumors and infection, may present with focal bony uptake. 28
Magnetic Resonance (MR) Imaging
Magnetic resonance (MR) imaging is becoming a more common diagnostic tool for evaluating stress fractures, and is now considered the standard. Magnetic resonance imaging has improved specificity over the bone scan, and is equally sensitive. Shin et al. 31 have shown an improved accuracy rate with MR imaging over bone scan in diagnosing femoral neck stress fractures in endurance athletes (Fig. 1B). Arendt and Griffiths 32 and Fredericson et al. 33 have proposed grading systems for stress fractures, utilizing MR imaging. In the early development of stress fractures, the STIR images are positive, followed by the T2 images, and then finally the T1 images. Stress fractures diagnosed and treated when only the STIR or T2 images are positive recover much more quickly than those fractures that are present on the T1 images.
The differential diagnosis of stress fractures includes other overuse injuries. Tendon or muscle injuries, exertional compartment syndrome, and superficial nerve entrapments must be excluded. Medial tibial stress syndrome (shin splints or periostitis) present similarly to stress fractures. Bone scan and MR imaging can differentiate these two entities. Other, less common disorders, such as tumors, infection, or avascular necrosis, should be considered in individuals who do not present with the usual history or do not respond to activity modifications. Osteoid osteoma and Brodie abscess are specific examples that need to be considered in the differential diagnosis.
Most stress fractures can be treated nonoperatively. The most important treatment modality is to convince the athlete to avoid the aggravating activity. Pain control can usually be achieved with nonsteroidal anti-inflammatory drugs, ice, and elevation. Ultrasound treatment is avoided, as it will cause pain at the fracture site. Athletes that remain symptomatic with activities of daily living should be placed on crutches and allowed protected weight bearing. Bracing or casting is only rarely required. However, fractures of the tarsal navicular and fifth metatarsal require more aggressive nonoperative treatment, including non-weight bearing and casting. 2 In addition, tibial stress fractures may heal more quickly when treated with a pneumatic leg brace. 34 Most stress fractures will heal in 6 to 8 weeks.
During this period of rest, athletes should be encouraged to maintain flexibility, muscle strength, and cardiovascular fitness. This can be done with stretching, swimming, cycling, and weight lifting. This cross training should be as sport-specific as possible, to maintain the athlete's skills. 28
The athlete may resume sports on a gradual basis when they are pain-free and non-tender. Radiographs should demonstrate evidence of healing, but it is not usually necessary to wait for complete radiographic union. Athletes must understand that the return to activity should be gradual and pain-free.
Identification and correction of predisposing factors can help prevent the initial development of stress fractures or keep athletes from sustaining recurrent fractures. This is particularly true in high-risk sports, such as track and field. The athlete's footwear should be inspected for wear, and running shoes must be replaced frequently. Orthotics may be prescribed in athletes with foot deformities. The surface that the athlete trains on should be monitored. Training on uneven ground or on very hard surfaces should be avoided. The conditioning program must be supervised to prevent overtraining or incorrect training. The most common mistakes the athlete makes are excessive mileage, excessive intensity, or a too rapid increase in training. 35 Conditioning must be individualized, and the development of a structured training program that the athlete agrees to follow has been shown to decrease the incidence of stress fractures. 36 In general, mileage should not be increased more than 10% per week, and total mileage should not exceed fifty miles per week. 35 The athlete should be encouraged to cross-train, and strength training should be incorporated into the female athlete's regimen, as improved muscle mass may decrease the risk of stress fractures.
Female athletes need to be carefully screened for eating disorders and menstrual abnormalities. A low-fat, high-protein diet with adequate calories is necessary to prevent a negative energy balance. In addition, the female athlete should consume at least 1500 mg of calcium per day, along with 400 to 800 International Units per day of vitamin D. Sodas containing phosphates should be avoided, as there is evidence that excess phosphate consumption may be involved in poor bone health. 2
Oral contraceptives pills, which are commonly used by female athletes as hormone replacement therapy, may decrease the risk of stress fractures. 21 However, the evidence regarding this practice is inconclusive. Calcitonin and bisphosphonates are frequently used in the treatment of postmenopausal osteoporosis, but the use of these medications is not approved in the premenopausal athlete. 12
Treatment of the athlete that demonstrates the female athlete triad is difficult. A multidisciplinary approach that involves the physician, trainer, nutritionist, and psychotherapist is required. Early identification of at-risk athletes is important, and the medical staff should screen for potential eating disorders and amenorrhea during the preseason physicals. Sanborn et al. suggest that a written contract be established that details the criteria the athlete must meet before she is able to compete. 15 This will usually involve weight gain, regular menses, and compliance with psychotherapy.
Surgical treatment of stress fractures is rarely required, and is usually limited to fractures that have failed a prolonged course of nonoperative treatment. In addition, displacement of a stress fracture is often an indication for operative management. This is the case in stress fractures involving the femoral shaft. These injuries are more common than previously thought, and nearly always heal with nonoperative management. 6 Displaced fractures of the femoral shaft have been reported; they require operative intervention. 37–39 Stress fractures of the patella, medial malleolus, and hallux sesamoids are other uncommon stress fractures that may require operative intervention. 40 Internal fixation is recommended for transverse patellar stress fractures, and medial malleolar fractures with a visible fracture line on plain radiograph results. 41,42 Bone grafting or excision of the great toe sesamoid is indicated for stress fractures that do not respond to nonoperative treatment. 43 Fractures of the femoral neck, anterior cortex of the mid-tibia, tarsal navicular, and fifth metatarsal are particularly troublesome, and will be discussed in detail. These fractures are seen commonly in the female athlete and can have a devastating effect on the athlete's career.
Femoral Neck Stress Fractures
Stress fractures of the femoral neck are more common in female athletes. One prospective study of track and field athletes found that 14% of stress fractures in females involved the femoral neck, while no male athlete had a stress fracture involving the femur. 3 A high index of suspicion and early diagnosis is paramount, given the potential disastrous complications resulting from fracture displacement.
The athlete with a femoral neck stress fracture will present with activity-related groin pain or pain referred to the knee. Physical examination will often reveal an antalgic gait, decreased range of motion, and pain with the hop test or heeltap test. Plain radiographs may be negative early, but the diagnosis can be confirmed with scintigraphy or MR imaging (Fig. 1A and B).
Femoral neck stress fractures can be classified as compression-sided injuries, tension-sided injuries, or displaced fractures. 44 Compression-sided stress fractures are usually treated with protective weight-bearing and gradual return to activity. However, athletes that remain symptomatic despite protective weight bearing, or athletes who have involvement of the majority of the femoral neck on radiographs, are candidates for operative stabilization utilizing cannulated screws.
Fractures that involve the tension side of the femoral neck are cause for the most concern. Successful treatment of these injuries with strict bed rest until the patient is pain-free, followed by protective weight-bearing, has been reported. 44,45 However, we feel that these injuries should be immediately stabilized with cannulated screws (Fig. 2A and B). Operative morbidity is minimal, and fracture displacement is associated with poor long-term function.
Displaced femoral neck stress fracture is a surgical emergency. Anatomic reduction and surgical stabilization should be performed within 8 hours to minimize the chance of nonunion or avascular necrosis. 46 Anatomic reduction must be achieved for best results, and open reduction should be performed if an adequate reduction cannot be obtained with closed manipulation.
The outcome of femoral neck stress fractures treated operatively is poor in athletes. No athlete was able to return to a preinjury activity level, and 70% of the athletes reported poor results in a series of 16 operatively treated femoral neck stress fractures. 47 Femoral neck stress fractures are the most serious stress injury to affect the female athlete, and successful management requires early diagnosis and treatment.
Anterior Cortex of the Mid-Tibia
Tibial stress fractures are the most commonly diagnosed stress fractures in both female and male athletes. 3–5 These fractures usually involve the posterior aspect of the tibia, and heal predictably with nonoperative treatment. However, fractures that involve the anterior cortex of the middle tibia are more problematic. Radiograph results of these injuries will reveal a radiolucent line through the anterior cortex of the tibia, which has been termed the “dreaded black line.” Fixation may be necessary for the fractures that remain symptomatic despite appropriate nonoperative treatment. 2,48 Unfortunately, the ability of athletes to return to their previous level of activity is doubtful after this type of injury. 49
Tarsal Navicular Stress Fractures
Tarsal navicular stress fractures are more common in the female athlete than previously thought. These injuries accounted for nearly 20% of all stress fractures in female collegiate athletes, in one prospective series. 5 Tarsal navicular stress fractures usually affect athletes involved in sports that require frequent sprinting and jumping.
The athlete will present will an insidious onset of activity-related medial foot pain that is frequently described as a cramp. There is tenderness over the medial midfoot, swelling, and loss of subtalar motion. Radiographic evaluation of these injuries is difficult, as the navicular is oblique in its orientation. The fracture occurs in the central third of the bone and lies in the sagittal plane (Fig. 3A). 50 Scintigraphy will reveal increased uptake, but is not specific for a tarsal navicular stress fracture. Magnetic resonance imaging or computed tomography will usually confirm the diagnosis (Fig. 3B).
Torg et al. 50 described a treatment algorithm in their series of 21 tarsal navicular stress fractures. Partial or complete but nondisplaced fractures were treated with a nonweight-bearing cast for 6 to 8 weeks. Fractures that were displaced or failed to heal were treated with internal fixation and bone grafting (Fig. 3C). Seventeen of the 21 patients were asymptomatic at follow-up. The four patients that were treatment failures were treated with prolonged nonweight-bearing, without bone grafting or internal fixation. Khan et al. 51 reported the successful management of tarsal navicular stress fractures with nonweight-bearing cast treatment in over 80% of patients. The authors recommended this treatment regimen even in patients who have failed previous treatments that involved weight-bearing activities. As with femoral neck fractures, a high index of suspicion and early treatment will give the athlete the best chance of returning to full activity.
Fifth Metatarsal Fractures
Fifth metatarsal stress fractures are relatively common, particularly in basketball players. Injuries to this bone occur in three distinct locations. Acute injuries are either avulsion fractures at the tuberosity, or fractures at the metaphyseal–diaphyseal junction (Jones fracture). Stress fractures usually occur more distally in the proximal diaphysis. 52 Torg et al. 53 have classified fifth metatarsal stress fractures into acute injuries, delayed unions, and nonunions.
Management of delayed unions and nonunions requires operative intervention with internal fixation. Bone grafting may also be necessary. Management of the acute Jones fracture and the more distal acute stress fracture is more controversial. These injuries usually heal in 6 to 8 weeks with treatment in a nonweight-bearing cast. However, prolonged healing has been reported in up to 28% of these injuries. 54 Early intramedullary fixation in élite athletes has been reported to allow earlier return to sports, but there have been no comparative studies demonstrating an advantage of operative therapy over nonoperative treatment. 55,56
Stress fractures are common overuse injuries in the female athlete. The pathogenesis of stress fractures is complex, and involves the interaction of a number of different variables. Bone mineral density, hormonal balance, and nutritional status are variables that are particularly important in the female athlete. Early recognition of the female athlete triad and aggressive treatment with a multidisciplinary approach is key to preventing stress fractures and maintaining bone health in the female athlete.
Diagnosis of stress fractures can usually be made by history and physical examination, along with confirmatory imaging studies. Magnetic resonance imaging is becoming increasingly useful in the diagnosis of stress fractures. Most stress fractures are treated nonoperatively. Stress fractures of the femoral neck, anterior cortex of the tibia, tarsal navicular, and fifth metatarsal are particularly concerning, because of the high incidence in female athletes and the potentially high morbidity associated with these injuries. A high index of suspicion and early treatment will allow for the successful nonoperative management of these high-risk fractures. Further research into the pathogenesis of stress fractures in the female athlete will allow those caring for these women to modify key risk factors and prevent injury.
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Nicola Maffulli, M.D., Guest Editor