The incidence of stress fractures in the general athletic population is less than 1%, but may be as high as 15% in runners. Stress fractures of the foot and ankle account for almost half of bone stress injuries in athletes. These injuries occur because of repetitive submaximal stresses on the bone resulting in microfractures, which may coalesce to form complete fractures. Advanced imaging such as MRI and triple-phase bone scans is used to evaluate patients with suspected stress fracture. Low-risk stress fractures are typically treated with rest and protected weight bearing. High-stress fractures more often require surgical treatment.
Key points
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Stress fractures of the foot and ankle are common in running and jumping athletes, and can result in significant disability and time away from sport.
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Bone scintigraphy and MRI are highly sensitive in evaluating athletes with suspected stress fracture, with the latter displaying higher specificity.
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Relative rest and gradual return to play is successful in treating most low-risk stress fractures.
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High-risk stress fractures often require operative treatment and can result in significant time away from sport.
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Bone stimulators and shock wave therapy have garnered significant interest, but have yet to be proved efficacious in the treatment of bone stress injuries.
Introduction
Epidemiology
Foot and ankle stress fractures are a major cause of disability in athletes of all types. Although the incidence of stress fractures in the general athletic population is less than 1%, the incidence may be as high as 15% in runners. Stress fractures in military recruits have been studied extensively. The military recruit population is at particular risk because of the abrupt and rigorous nature of basic training. In a systematic review of the military literature, Wentz and colleagues found a stress fracture incidence of 3% and 9.2%, in men and women respectively. The most common sites of stress fracture in both the military and athletic population are the leg and ankle. In a study of division I collegiate athletes over a 5-year period, the incidence of stress fracture was 1.4%. Foot, ankle, and tibia stress fractures were the most common, and sports with the highest rate of stress fracture were cross-country and track. In a recent study of stress fractures in high school athletes, Changstrom and colleagues reported a 0.8% incidence of stress fractures over a 7-year period, including more than 25 million athlete exposures. They reported a higher rate of stress fractures in women, and the lower leg and foot accounted for 40.3% and 34.9% of stress fractures respectively. Sports with the highest rates of stress fractures were girls’ cross-country, girls’ gymnastics, and boys’ cross-country.
Causes and Pathogenesis
Stress fractures of bone result from submaximal, repetitive loading resulting in an imbalance between bone resorption and formation. Athletes at highest risk are those who abruptly increase the duration, intensity, or frequency of physical activity without adequate periods of rest. These phenomena result in increased osteoclastic activity, leading to increased bone resorption and lagging bone formation. Ultimately the bone fatigues, and if there are intense and repetitive activities, microfractures may result. Stress injuries occur along a continuum, and a stress reaction is a bone stress injury resulting from microfracture without a defined fracture line on imaging. Continued stress to the bone results in coalescences of multiple microfractures, leading to a visible and defined stress fracture.
Intrinsic and extrinsic factors affect the development of stress fractures. Intrinsic factors related to stress fractures include age, sex, bone mineral density, malalignment, hormonal imbalance, and poor vascular supply. Extrinsic factors are more easily modifiable and include activity type, intensity of training, training surface, improper technique or equipment, and poor nutrition. Decreased bone mineral density has been correlated with increased stress fracture risk and may be related to diet, age, and hormone imbalance. The female athlete triad (eating disorder, amenorrhea, and osteoporosis) refers to the phenomena most commonly seen in competitive female athletes involved in long-distance running, gymnastics, and figure skating. Barrack and colleagues showed that the cumulative risk for bone stress injuries increased with increasing number of triad-related risk factors. Particular attention must be paid to these modifiable risk factors, and a dietary and menstrual history should be obtained when interviewing a female athlete.
History, Physical Examination, and Imaging
Athletes presenting with foot and ankle stress fractures often describe a progressive and insidious onset of pain and swelling. A thorough history should include details on the athletes: intensity of training, duration of training, and changes in training surface or footwear. General medical information, including diet, nutrition, and in female athletes menstrual cycles, should be gathered. Physical examination focuses on weight-bearing alignment and range of motion. Areas of pain, tenderness, and swelling indicate areas of possible bone stress injury.
Imaging studies, including radiographs, computed tomography (CT), MRI, and bone scan, are helpful in evaluating patients for foot and ankle stress injuries. Initial and follow-up radiographs may be negative in as many as 85% and 50% of patients respectively.
Bone scintigraphy is highly sensitive in evaluating bone stress injuries, and until the advent of MRI it was considered the gold standard. Three-phase bone scan is recommended rather than other methods of bone scintigraphy because it allows differentiation between soft tissue and bony uptake. The sensitivity of bone scan is close to 100%, but it lacks specificity, with false-positive results possible with tumors, infections, and infarction.
MRI has become increasingly popular in the evaluation of bone stress injuries because of its high sensitivity and specificity. The added benefit of being able to evaluate the surrounding soft tissues for other pain-generating disorders makes MRI particularly attractive when evaluating patients with suspected bone stress injuries. CT lacks the sensitivity of MRI, but is useful in defining fracture characteristics. The high-quality cross-sectional imaging produced with CT allows better definition of fracture lines, areas of sclerosis, and comminution.
High-risk and Low-risk Stress Fractures
Stress fractures can be categorized as either high risk or low risk based on their propensity to heal. High-risk stress fractures have a greater risk of complete fracture or nonunion, and often require prolonged periods of non–weight-bearing immobilization or surgical treatment. Stress fractures, including navicular, medial malleolus, talus, hallucal sesamoid, and proximal fifth metatarsal, are considered high risk. Low-risk stress fractures, such as calcaneus, lateral malleolus, and metatarsal shafts, are generally treated successfully with relative rest and symptomatic relief. Patients with low-risk stress fracture typically make a full recovery without long-term adverse effects.
Introduction
Epidemiology
Foot and ankle stress fractures are a major cause of disability in athletes of all types. Although the incidence of stress fractures in the general athletic population is less than 1%, the incidence may be as high as 15% in runners. Stress fractures in military recruits have been studied extensively. The military recruit population is at particular risk because of the abrupt and rigorous nature of basic training. In a systematic review of the military literature, Wentz and colleagues found a stress fracture incidence of 3% and 9.2%, in men and women respectively. The most common sites of stress fracture in both the military and athletic population are the leg and ankle. In a study of division I collegiate athletes over a 5-year period, the incidence of stress fracture was 1.4%. Foot, ankle, and tibia stress fractures were the most common, and sports with the highest rate of stress fracture were cross-country and track. In a recent study of stress fractures in high school athletes, Changstrom and colleagues reported a 0.8% incidence of stress fractures over a 7-year period, including more than 25 million athlete exposures. They reported a higher rate of stress fractures in women, and the lower leg and foot accounted for 40.3% and 34.9% of stress fractures respectively. Sports with the highest rates of stress fractures were girls’ cross-country, girls’ gymnastics, and boys’ cross-country.
Causes and Pathogenesis
Stress fractures of bone result from submaximal, repetitive loading resulting in an imbalance between bone resorption and formation. Athletes at highest risk are those who abruptly increase the duration, intensity, or frequency of physical activity without adequate periods of rest. These phenomena result in increased osteoclastic activity, leading to increased bone resorption and lagging bone formation. Ultimately the bone fatigues, and if there are intense and repetitive activities, microfractures may result. Stress injuries occur along a continuum, and a stress reaction is a bone stress injury resulting from microfracture without a defined fracture line on imaging. Continued stress to the bone results in coalescences of multiple microfractures, leading to a visible and defined stress fracture.
Intrinsic and extrinsic factors affect the development of stress fractures. Intrinsic factors related to stress fractures include age, sex, bone mineral density, malalignment, hormonal imbalance, and poor vascular supply. Extrinsic factors are more easily modifiable and include activity type, intensity of training, training surface, improper technique or equipment, and poor nutrition. Decreased bone mineral density has been correlated with increased stress fracture risk and may be related to diet, age, and hormone imbalance. The female athlete triad (eating disorder, amenorrhea, and osteoporosis) refers to the phenomena most commonly seen in competitive female athletes involved in long-distance running, gymnastics, and figure skating. Barrack and colleagues showed that the cumulative risk for bone stress injuries increased with increasing number of triad-related risk factors. Particular attention must be paid to these modifiable risk factors, and a dietary and menstrual history should be obtained when interviewing a female athlete.
History, Physical Examination, and Imaging
Athletes presenting with foot and ankle stress fractures often describe a progressive and insidious onset of pain and swelling. A thorough history should include details on the athletes: intensity of training, duration of training, and changes in training surface or footwear. General medical information, including diet, nutrition, and in female athletes menstrual cycles, should be gathered. Physical examination focuses on weight-bearing alignment and range of motion. Areas of pain, tenderness, and swelling indicate areas of possible bone stress injury.
Imaging studies, including radiographs, computed tomography (CT), MRI, and bone scan, are helpful in evaluating patients for foot and ankle stress injuries. Initial and follow-up radiographs may be negative in as many as 85% and 50% of patients respectively.
Bone scintigraphy is highly sensitive in evaluating bone stress injuries, and until the advent of MRI it was considered the gold standard. Three-phase bone scan is recommended rather than other methods of bone scintigraphy because it allows differentiation between soft tissue and bony uptake. The sensitivity of bone scan is close to 100%, but it lacks specificity, with false-positive results possible with tumors, infections, and infarction.
MRI has become increasingly popular in the evaluation of bone stress injuries because of its high sensitivity and specificity. The added benefit of being able to evaluate the surrounding soft tissues for other pain-generating disorders makes MRI particularly attractive when evaluating patients with suspected bone stress injuries. CT lacks the sensitivity of MRI, but is useful in defining fracture characteristics. The high-quality cross-sectional imaging produced with CT allows better definition of fracture lines, areas of sclerosis, and comminution.
High-risk and Low-risk Stress Fractures
Stress fractures can be categorized as either high risk or low risk based on their propensity to heal. High-risk stress fractures have a greater risk of complete fracture or nonunion, and often require prolonged periods of non–weight-bearing immobilization or surgical treatment. Stress fractures, including navicular, medial malleolus, talus, hallucal sesamoid, and proximal fifth metatarsal, are considered high risk. Low-risk stress fractures, such as calcaneus, lateral malleolus, and metatarsal shafts, are generally treated successfully with relative rest and symptomatic relief. Patients with low-risk stress fracture typically make a full recovery without long-term adverse effects.
Low-risk stress fractures
Fibular Stress Fractures
Fibular stress fractures are rare in the athletic population. These fractures, termed runners fractures, are most commonly seen in running athletes. In a study of 320 athletes, stress fractures of the fibula accounted for 6.6% of all stress fractures.
Stress fractures of the fibula may occur along the entire length of the fibula, but are most commonly seen in the distal third in the athletic population. In Burrows’ study of fibula stress fractures, he noted that most fractures in runners occurred in the cortical area of the distal fibula just proximal to the syndesmotic ligaments, approximately 50 mm (2 inches) or more above the tip of the malleolus. In a later study of 50 fibular stress fractures in athletes, Devas and colleagues reported similar findings, with the most common location of fracture being 4 to 7 cm above the tip of the lateral malleoli ( Fig. 1 ).
Fibula stress fractures are thought to result from a combination of muscular forces and repetitive axial loading. Axial force transmission through the fibula during weight-bearing activities varies between 2.3% and 10.4% depending on ankle position and limb orientation. Muscular forces during running are thought to play a role in fibular stress fractures; namely, strong contraction of the ankle flexors is thought to result in approximation of the distal tibia and fibula, with resultant increased stress in the area superior to the distal tibia-fibular syndesmosis. Other factors, including shoe wear, training surface, and metabolic disease, have been implicated in causing these fractures.
Evaluation of a patient with a potential fibular stress fractures should involve a thorough history, including change in footwear, running surface, or intensity of training. Patients often describe increased pain and swelling in the area of the distal fibula with an insidious onset or an acute episode of pain without specific trauma.
Radiographs are often negative for up to 3 weeks after the initiation of pain. Three-phase bone scan is the most sensitive test to identify early stress fractures or stress reaction when radiographs are negative. MRI has become popular in the imaging of stress fracture because of its high sensitivity and specificity. In addition, MRI can be used to evaluate other conditions in the differential diagnosis. Conditions included in the differential diagnosis of fibular stress fracture are tendonitis, neoplasm, osteochondral lesion of the tibia or talus, peroneal tendon dislocation, exertional compartment syndrome, and fascial hernias.
Stress fractures of the distal fibula respond favorably to nonoperative treatment. Most investigators recommend a period of relative rest and activity modification. Athletes are allowed to cross-train during this period. In patients who present with a limp, a short period of non–weight-bearing immobilization may be indicated. Return to activity is allowed when tenderness at the fracture site abates and signs of radiographic healing are present. Contact athletes usually return to play 6 to 8 weeks from the initiation of symptoms. The author is unaware of any reports of operative treatment of these fractures.
Calcaneus Stress Fracture
Stress fractures of the calcaneus most commonly affect military recruits and long-distance runners. The 2 largest series of calcaneus stress fractures published to date involved a population of military recruits. Symptoms typically presented insidiously, and were worsened by activity and relieved with rest. Examination of the affected foot may reveal swelling, and pain may be present with compression of the heel. In both of these series, stress fractures were most commonly localized to the posterior tuberosity along the trabecular stress lines. Radiographs typically reveal a sclerotic line after 2 to 3 weeks of symptoms, but may initially be negative, often leading to a delay in diagnosis. The differential diagnosis includes plantar fasciitis, Baxter neuritis, insertional Achilles tendonitis, retrocalcaneal bursitis, and calcaneal apophysitis in adolescents.
In cases of suspected stress fracture, MRI helps to delineate the diagnosis. In a recent MRI study of Finnish military recruits, 56% of fractures were localized to the posterior tuberosity ( Fig. 2 ) and 44% of stress fractures were located at the anterior and middle portions of the calcaneus. MRI seems to have a significant advantage in diagnosing stress fractures in the anterior part of the calcaneus, and often identifies other associated tarsal stress injuries. MRI is recommended because of its high sensitivity and specificity and its usefulness in the evaluation of other soft tissue disorders.
Calcaneus stress fractures are treated successfully with rest and protected weight bearing followed by reintroduction to training in most patients. Leabhart noted that reintroduction to training before 8 weeks of convalescence led to a recurrence of symptoms.
More recently in the literature several case reports have detailed stress fractures of the anterior process of the calcaneus in athletes. In 2 of these case reports the fractures were associated a calcaneonavicular coalition. In 1 case a calcaneonavicular bar was resected with screw fixation across the stress fracture at the anterior process. Further evidence is needed to support operative versus nonoperative treatment of stress fracture of the anterior process of the calcaneus.
Stress fractures of the calcaneus may be more frequent than is reported in the literature, and are likely misdiagnosed as more common ailments of the hindfoot and ankle. Nonoperative treatment including rest and protected weight bearing is effective in treating most cases.
Metatarsal Shaft Stress Fractures
Stress fractures of the metatarsals are common in running athletes and represent up to 20% of stress fractures in the athletic population. Metatarsal shaft stress fractures are most common at the second and third metatarsals, and are often referred to as march fractures because of the high incidence in military trainees. These fractures typically occur after an increase in exercise intensity or change in training surface. Physical examination often reveals swelling, point tenderness at the fracture site, and tenderness with metatarsal stress testing. Differential diagnosis includes Morton neuroma, metatarsophalangeal joint synovitis, metatarsalgia, infection, or rarely neoplasm.
Radiographs are typically negative for up to 3 weeks. Empiric treatment is typically initiated with suspected stress fractures, and radiographs repeated 2 to 3 weeks after initiation of symptoms confirm the diagnosis, with callus and fracture line typically noted ( Fig. 3 ). In athletes who are unable or unwilling to interrupt their training, MRI is indicated because of its increased sensitivity.
Treatment of nondisplaced metatarsal stress fracture is nonoperative with weight bearing to tolerance in a postoperative shoe or prefabricated walker boot. Patients are allowed to gradually return to activity when tenderness and swelling have resolved and radiographic evidence of healing is present, typically 4 to 6 weeks after initiation or symptoms.
High-risk stress fractures
Medial Malleolar Stress Fracture
Stress fractures of the medial malleolus are rare, with an incidence of 0.6% to 4.1% reported in the literature. Stress fractures of the medial malleolus are typically seen in running and jumping athletes, and are thought to result from torsional forces imposed on the medial malleolus during repetitive loading. More recently an association between anterior impingement lesions has been suggested as a potential cause for these rare fractures.
Medial malleolus stress fractures typically present with vague anterior medial ankle pain. Patients may complain of minor preceding trauma, with continued tenderness at the anterior medial ankle with activity. The pain is often relieved with rest, but persists with activity. Inspection may reveal swelling about the medial ankle. Anterior medial ankle impingement is associated with the condition and stress fractures may be difficult to discern from anterior medial ankle impingement symptoms. Palpation over the medial malleolus may elicit tenderness and increases the index of suspicion. The differential diagnosis includes posterior tibial tendonitis, deltoid ligament injuries, ankle arthritis, impingement, and tarsal tunnel syndrome.
Medial malleolar stress fractures present in a characteristic pattern: arising from the medial shoulder of the tibial plafond, the fracture line runs either obliquely or vertically to the medial tibial cortex ( Fig. 4 A ). This pattern is similar to the typical supination-adduction pattern of fracture described by Lauge-Hansen. Initial radiographs of the ankle may be negative in up to 70% of cases. If stress reaction or occult stress fracture is suspected, an MRI or bone scan should be obtained, with the latter reported to have close to 100% sensitivity. Although bone scan remains the gold standard for diagnosis of stress-related injuries, MRI has the advantage of increased specificity, is noninvasive, and provides multiplanar images that may help guide treatment. In addition, MRI allows the differentiation of stress reactions and stress fractures. CT provides excellent resolution and is useful in defining the extent of the fracture, areas of sclerosis, and associated impingement lesions ( Fig. 4 B, C).
Initial treatment of patients with stress reactions of the medial malleolus is a short period of immobilization and activity modification. Return to activity is gradual and is based on resolution of swelling and tenderness. Nonoperative and operative treatment strategies have been advocated for stress fractures of the medial malleolus. In high-level or in-season athletes with a radiographically detectable fracture line, or in patients with displaced fractures, operative treatment has been recommended. A variety of operative treatment strategies have been described, including isolated drilling, percutaneous fixation with 4-mm cannulated screws, and open reduction internal fixation with 4-mm cannulated screws. Associated disorders should be addressed, including ankle instability, bony impingement lesions, and malalignment. Postoperative protocols vary widely in published studies of operatively treated patients, with a period of non–weight bearing of 1 to 3 weeks observed in most patients followed by gradual return to activity.
The author’s review of the literature produced only 1 report of a medial malleolar stress fracture nonunion. The patient presented 2 years after seeking initial treatment with a hypertrophic nonunion of the medial malleolus. The patient was treated with open reduction and internal fixation and bone grafting. The patient returned to activity at 4.5 months, and achieved union of the fracture on radiographs at 7 months postoperatively.
Current literature lacks consistent treatment protocols for operative and nonoperative management of medial malleolar stress fractures. In general, both operative and nonoperative treatment have been successful in treating these fractures. In a systematic review of the literature, Irion and colleagues reported an average return to play of 7.6 and 2.4 weeks for nonoperatively treated and operatively treated patients respectively. In patients desiring an expedited return to activity, surgical management may be more effective based on the current literature.
Navicular Stress Fractures
Stress fractures of the tarsal navicular are uncommon in the general athletic population, but may account for 15% to 32% of stress-related fractures in track and field athletes. The tarsal navicular lies between the talar head and the 3 cuneiforms at the medial midfoot. The blood supply to the navicular is derived from the medial tarsal branch of the dorsalis pedis artery and a branch of the tibialis posterior artery. A watershed area exists at the central third of the bone and has been implicated in stress injuries to the tarsal navicular. Anatomic variation, including a short first ray and long second metatarsal, have been proposed as potential risks factors as well. Fitch and colleagues expanded on this concept, relating that the compression forces exerted by the second metatarsal and middle cuneiform at the lateral navicular create an area of maximal shear stress at the central third of the navicular. The high level of force transmission at the central third of the navicular, together with the tenuous blood supply at the central third of the navicular, is postulated to predispose this area of the bone to stress injuries.
Navicular stress fractures can be difficult to identify and examiners should have a high index of suspicion in athletes involved in high-risk sports; namely football, rugby, track and field, and basketball. Typical presentations involve an insidious onset of pain without swelling or an inciting event. These injuries can be difficult to detect, and frequently go undiagnosed for several months after the initiation of symptoms. Examiners must have a high index of suspicion in athletes with medial foot and ankle pain. Tenderness at the proximal dorsal potion of the navicular, termed the N spot, is present in 81% of patients with navicular stress fracture. Athletes with tenderness at the N spot should have a further work-up to rule out a stress fracture.
Plain radiographs are initially obtained, but lack sensitivity in diagnosing even complete fractures of the tarsal navicular. Khan and colleagues reported a 76% false-negative rate for incomplete fracture and 19% false-negative rate for complete fractures in his review of the literature. Bone scan is inexpensive and has long been the gold standard for initial evaluation of the navicular stress fracture. Sensitivity of triple-phase bone scans is close to 100%, but specificity is low. Bone scans indicating a stress injury should be further evaluated with a follow-up CT scan or MRI. CT scans differentiate stress reaction from stress fracture, and provide detailed imaging of the fracture, including potential comminution, sclerosis, or degenerative changes. Navicular stress fractures typically arise in the central third of the bone starting proximal dorsal and progressing in a distal plantar direction ( Fig. 5 ). Saxena and colleagues proposed a CT-based classification system based on the propagation of the fracture line through the navicular body ( Table 1 ).
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