Contents

Overview 2

Pathophysiology 3

Risk Factors 4

Epidemiology 5Epidemiologic features based on location and activity 5Epidemiological features based on sex 6Epidemiological features based on race 6

Clinical Presentation 7History 7Physical examination 7

Diagnostic Testing and Grading of Stress Fractures 7Radiography 7Technetium-99m bone scanning 7Magnetic resonance imaging 8Grading of stress fractures 8

Treatment, Prevention, and Complications 9Treatment 9Prevention 10Complications 11

1

Overview

The stress fracture is a common overuse injury seen in athletes and military recruits.[1, 2] Breithaupt originally described this injury in 1855.[3] The injury is usually seen in the lower extremities, but it has also been reported in the upper extremities and the ribs. The most common locations for stress fractures include the tibia, metatarsals, fibula, and navicular bones. Less common locations include the femur, pelvis, and sacrum.

A stress fracture is caused by repetitive and submaximal loading of the bone, which eventually becomes fatigued and leads to a true fracture. The typical presentation is a complaint of increasing pain in the lower extremity during exercise or activity. The patient's history usually reveals a recent increase in either training volume or intensity.

The treatment of most stress fractures is relatively straightforward and includes decreased activity and immobilization; however, patients with some stress fractures, such as displaced femoral neck stress fractures and fifth metatarsal base stress fractures, are more likely to have complications such as nonunion.[4, 5] These complications should be monitored closely because surgical intervention may be necessary.

An image depicting a stress fracture can be seen below

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Fifth metatarsal stress fracture.

Pathophysiology

Stress fractures result from recurrent and repetitive loading of bone. The stress fracture differs from other types of fractures in that, in most cases, no acute traumatic event precedes the symptoms.

Normal bone remodeling occurs secondary to increased compressive or tensile loads or increased load frequency. In the normal physiologic response, minor microdamage of the bone occurs. This is repaired through remodeling. Stress fractures develop when extensive microdamage occurs before the bone can be adequately remodeled.[6, 7]

Often, the patient has a history of an increase and/or change in the character of activity or athletic workouts. Bones may be more prone to stress fractures if the bone is weakened, as in individuals with osteoporosis, or in those in whom weight-bearing activities are increased.

The 3 factors that can predispose an individual to the development of stress fractures are an increase in the applied load, an increase in the number of applied stresses, or a decrease in the surface area of the applied load.[8]

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The applied load on the bone may be increased by decreasing the surface area that the weight is distributed across or by increasing the total weight applied to the bone. High-impact activities, such as jumping or performing plyometrics, running on a new surface, or practicing incorrect biomechanical movements or techniques, may increase the risk of stress fractures.

Risk Factors

Although stress fractures result from repeated loading, the exact contribution of training factors (volume, intensity, surface) has not been clearly established.[9]From what we do know, menstrual disturbances, caloric restriction, decreased bone density, muscle weakness, and leg-length differences are risk factors for stress fractures.[10, 11]

Myburgh reported that stress fractures were more common in athletes that had decreased bone density, lower dietary calcium intake, current menstrual irregularity, and less oral contraceptive use, when the athletes were matched for similar training volume and intensity.[12]

Nattiv and Armsey found that genetics, female sex, white ethnicity, low body weight, lack of weight-bearing exercise, intrinsic and extrinsic mechanical factors, amenorrhea, oligomenorrhea, inadequate calcium and caloric intake, and disordered eating are additional risk factors for stress fractures.[13] A decreased testosterone level in male endurance athletes has also been implicated as a risk factor for stress fractures.[14, 15, 16, 17]

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Schnackenburg et al did a matched control study on 19 female athletes with tibial stress fractures found that stress fracture patients had lower tibial cross-sectional areas, lower trabecular bone mineral densities, and less cortical area, as well as decreased knee extension strength. They suggested that impaired bone quality of the posterior cortex and decreased muscle strength were associated with stress fractures in the female athlete.[18]

Giladi identified 2 anatomic risk factors in military recruits. Recruits with stress fractures had significantly narrower tibiae and increased external rotation of the hip. These 2 variables were independent and cumulative, and in the presence of both risk factors, the stress-fracture morbidity rate was 45%.[19]

Epidemiology

Epidemiologic features based on location and activity

Table 1. Epidemiologic Features Based on Location and Activity 

Location of Fracture Activity Involved

Metatarsals, general Football, basketball, gymnastics, ballet, military training[20]

Metatarsal, base of the second Ballet

Metatarsal, fifth Tennis,[21, 22] ballet

Sesamoids of the foot Running, ballet, basketball, skating

Navicular Basketball, football, running

Talus Pole vaulting

Calcaneus Military drills, running, aerobics

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Fibula Running, aerobics, ballet, race-walking

Tibia Running sports, dancing, ballet

Patella Running, hurdling

Femoral neck Distance running, military training[23]

Pubic rami Military drills, distance running

Pars articularis Gymnastics, ballet, cricket, volleyball, diving, football

Chest, ribs Swimming,[24] golf,[25] rowing[26]

Sternum Wrestling[27]

Ulna Racquet sports, volleyball

Olecranon Baseball, throwing sports

Epidemiological features based on sex

Studies of US military recruits revealed a higher percentage of stress fractures in female recruits than in male recruits.[1, 28, 29, 30] Bennell et al also found a 45% incidence of stress fractures in competitive female runners.[6] The women most at risk for stress fractures were those who restricted their food intake and those who had dysmenorrhea.

The triad of disordered eating, amenorrhea, and osteoporosis are conditions that may be extremely prevalent in female distance runners and ballet dancers, as well as in other female athletes who believe that a low body weight or body-fat percentage provides a competitive advantage.[31, 32] The amenorrheic female athlete may experience a prolonged state of estrogen deficiency similar to that of a postmenopausal woman. The lower estrogen levels are associated with decreased bone density; even if normal menses returns, this bone loss may be irreversible in high school – and college-aged female athletes. Early identification of female athletes who are likely to develop the female athlete triad is important for the prevention of stress fractures and for maintaining overall future bone health.

Epidemiological features based on race

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In a study of military recruits, Markey found no difference in the incidence of stress fractures between recruits of various racial backgrounds.[33]

Clinical Presentation

History

With stress fractures, the typical complaint is that of an insidious onset of pain with activity or a complaint of pain in the affected extremity with repeated loading. Usually, the patient has no recent history of trauma to the affected area.

The pain subsides at rest, but symptoms return when the patient resumes the original activity. Local tenderness and swelling are often found at the fracture site. Early diagnosis is usually based on clinical findings, and several weeks may be required before the fracture site or new bone formation is visible on radiography.

The pain may occur only with weight bearing, and it may be reproducible with continued or prolonged activity. Some patients may associate a change in training equipment or training methods with the onset of symptoms.

Physical examination

The common findings on physical examination may include tenderness or pain on palpation or percussion of the bone. Erythema or edema may be present at the site

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of the stress fracture. Loading or stress of the affected bone may also produce symptoms.

Diagnostic Testing and Grading of Stress Fractures

Radiography

Stress fractures may not show up on radiographs for the first 2-4 weeks after injury. The first radiographic finding may be a localized periosteal reaction or an endosteal cortical thickening. The low sensitivity of radiographs for stress fractures makes bone scanning, magnetic resonance imaging (MRI), and computed tomography (CT) the preferred tests for diagnosis.

Technetium-99m bone scanning

Technetium bone scan findings may be positive in the case of a stress fracture after 72 hours; however, a positive bone scan finding is nonspecific, and it may be indicative of another diagnosis, such as an infection or a neoplastic process. Conventional radiography and bone scanning have been compared for the initial detection of stress fractures; positive findings were reported in 96% of bone scans, whereas only 42% positive findings were reported on radiographs.

Magnetic resonance imaging

MRI is also useful in the diagnosis of stress fractures. MRI provides information about bone integrity and fracture orientation, and it can demonstrate focal tissue damage and edema.

The MRI findings of stress fractures typically follow 1 of 2 patterns. In the first pattern, a hypointense, bandlike fracture line is visible with surrounding bone or tissue edema. The second MRI finding represents an amorphous stress fracture or response pattern. This MRI finding does not demonstrate an obvious fracture line or band; instead, the fracture may have diffuse or scattered areas of hypointensity on T1-weighted images, with increased signal intensity on T2-weighted images.[34]

Short-tau inversion recovery (STIR) imaging sequences suppress the normal fat signal intensity in bone marrow, allowing for better visualization of intramedullary bone.[35, 36, 37]

Grading of stress fractures

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Several grading systems for stress fractures based on MRI or scintigraphic findings have been proposed for correlationg imaging findings with clinical findings and providing treatment guidelines.[35]

Table 2. Grading of Stress Fractures on the Basis of Radiologic Findings[35] 

Grade Radiographic Finding

Bone Scan Finding MRI Finding

1 Normal Poorly defined area Increased activity on STIR image

2 Normal More intense Poor definition on STIR and T2-weighted images

3 Discrete line Sharp area of uptake No focal or fusiform cortical break on T1- and T2-weighted images

4 Fracture or periosteal reaction

More intense localized transcortical uptake

Fracture line on T1- and T2-weighted images

Treatment, Prevention, and Complications

Treatment

Most stress fractures can be treated conservatively by having patients stop or significantly decrease their activity for approximately 4-6 weeks, followed by a gradual return to activity. Patients with pain with walking may be placed in a short leg cast with crutches, a walking boot, or a brace for 4-6 weeks.

The use of pneumatic braces in the treatment and rehabilitation of tibial stress fractures also speeds the patient's return to training.[38]

Table 3. Healing Times for Various Stress Fractures*[39] 

Site of Stress Fracture

Percentage Healed at 2-4 wk, %

Percentage Healed at 1-2 mo, %

Percentage Healed at > 2 mo, %

Tibia, proximal third

0 43 57

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Tibia, middle third 0 48 52

Tibia, distal third 0 53 47

Fibula 7 75 18

Metatarsals 20 57 23

Sesamoids 0 0 100

Femur, shaft 7 7 86

Femur, neck 0 0 100

Pelvis 0 29 75

Olecranon 0 0 100

*Adapted from Hulkko (Findings were from a case series of 368 stress fractures in athletes, in which the healing times of stress fractures in different locations were assessed.)

Prevention

Nutritional measures: calcium supplementation

Regarding fracture risk, Schwellnus and Jordaan found no benefit with calcium supplementation (500 mg/d) beyond the usual dietary intake in male military recruits.[40]

Biomechanical measures: orthotics and shoe inserts

The use of orthotic devices and shoe inserts has been studied as a preventive measure for lower-extremity stress fractures. Finestone and Milgrom both studied the use of semirigid orthoses, soft orthoses, or both in the boots of military recruits during basic training.[41, 42]

Finestone found that the incidence of lower-extremity stress fractures was lower in the group using semirigid orthoses (15.7%) or soft biomechanical orthoses (10.7%) than in the control group (27%). Additionally, the recruits better tolerated the soft biomechanical orthoses than the semirigid orthoses.[41]

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In a prospective study of stress fractures, Milgrom et al studied the hypothesis that a shock-absorbing orthotic device worn within military boots decreases the incidence of stress fractures. Milgrom et al demonstrated a statistically significant decrease in the incidence of femoral stress fractures in the orthotic device group. In military recruits who did develop stress fractures, the time of onset and the location of stress fractures did not differ between the orthotic device group and the non–orthotic device group.[42]

Gillespie and Grant reviewed the use of shock-absorbing insoles in 4 trials. These insoles appeared to reduce the incidence of stress fractures and stress reactions of bone; however, incomplete data from one trial indicated that a reduction in the running distance and intensity may also have been a factor in preventing stress fractures.[38]

Complications

High-risk stress fractures

Nonunion of stress fractures is uncommon, but it can occur. These stress injuries should be closely followed up for early surgical intervention. These include stress fractures of the neck of the femur, the anterior cortex of the tibia, the tarsal navicular, and the bases of the second and fifth metatarsals.[39]

Other high-risk stress fractures include stress fractures of the patella and medial malleolus.[43] Anterior-cortex stress fractures of the tibia are considered high risk because the tensile forces across the anterior portion of the tibia can typically lead to delayed union or nonunion.

Low-risk stress fractures

Low-risk stress fractures include most upper-extremity stress fractures, with the possible exception of fractures through the physis of the humeral head (little

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leaguer's shoulder) and fractures through the medial epicondyle (little leaguer's elbow), which may have complications due to the involvement of the growth plate.

Other low-risk stress fractures include stress fractures of the ribs, pelvis, femoral shaft, fibula, calcaneus, and the metatarsal shafts.

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