The pathophysiology, diagnosis, and management of foot stress fractures.

C L I N I C A L F E AT U R E S

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The Pathophysiology, Diagnosis, and Management of Foot Stress Fractures

DOI: 10.3810/psm.2014.11.2095

James Pegrum, MB BS (Lon), BSc (Orthopaedics), MSc (Sports Medicine), MRCS (Eng), Diploma DMM UIAA 1 Vivek Dixit, MSc, MPhiL, MHSc (Public Health), PhD (Med), CAFÉ, PDCR, FASc (ASAW), FRSH, FHTA 2 Nat Padhiar, MSc, PhD, FCPodS FFPM RCPS (Glas) 3 Ian Nugent, MB, BS, FRCS 4 1 Oxford John Radcliffe Hospitals Orthopaedic Trauma Rotation, Stoke Mandeville Hospital, Aylesbury, Buckinghamshire, England; 2 Postdoctoral Fellow (Endocrinology & Metabolism), Faculty of Medicine, Hadasah Medical School, Hebrew University of Jerusalem, Ein Kerem Campus 91120, Israel; 3Consultant, Podiatric Surgeon, and Honorary Reader, Centre for Sport and Exercise Medicine, William Harvey Research Institute, Queen Mary, London University, London, England; 4Consultant Foot and Ankle Orthopaedic Surgeon, Royal Berkshire National Health Service Foundation Trust, Reading, England

Correspondence: James Pegrum, MB BS (Lon), BSc (Orthopaedics), MSc (Sports Medicine), MRCS (Eng), Diploma DMM UIAA, Oxford John Radcliffe Hospitals Orthopaedic Trauma Rotation, Stoke Mandeville Hospital, Aylesbury, Buckinghamshire, England HP21 8AL. Email: [email protected]

Abstract

Introduction: There is an increasing prevalence of osteoporosis, and with it a rise in the diagnosis of stress fractures. Postmenopausal women are particularly at risk of stress fractures. This review article describes the pathophysiology of foot stress fractures and the latest diagnostic and treatment strategies for these common injuries. Discussion: There are numerous risk factors for stress fractures that have been identified in the literature. Reduced bone mineral density is an independent risk factor for delayed union. Prevention of stress fractures with training periodization and nutritional assessment is essential, especially in females. Diagnosis of stress fractures of the foot is based on history and diagnostic imaging, which include radiographs, ultrasound, therapeutic ultrasound, computed tomography, and bone scans; however, magnetic resonance imaging is still the gold standard. Treatment depends on the bone involved and the risk of nonunion, with high-risk fractures requiring immobilization or surgical intervention. Patients presenting with underlying bone mineral deficiency treated without surgery require a longer period of activity modification. Training rehabilitation protocols are described for those with low-risk stress fractures. Results: A useful algorithm is presented to guide the clinician in the diagnosis and management of such injuries. Keywords: stress fractures; female quintuple; bone mineral density; foot; systematic review; osteoporotic fractures

Introduction

Overuse injuries in athletes has a prevalence of 76%.1 The lower limb accounts for 80% to 95% of stress fractures.2 There is increasing participation in endurance sports and marathon running, and the incidence of stress fractures in runners is 21% and higher in army recruits at 31%.3−6 The foot is a complex anatomical structure and is subjected to large forces during daily activities and during sports participation. Wolff7 described the internal structure of bone, and the ability to distribute loads is related to the direction of the stresses placed upon it. Therefore, identifying stress fractures that are prone to non-union, such as reduced bone mineral density (BMD), is essential.7,8 A worldwide estimate suggests that 1 billion people are vitamin D deficient, which may be a risk factor for stress fracture occurrence.9 Therefore, it is essential to appropriately differentiate stress fractures that result from reduced BMD or vitamin D deficiency, and those that are prone to nonunion due to the anatomical site.10 There is a spectrum of stress fracture presenting in the foot, which may lead to diagnostic delay and suboptimal treatment, resulting in unnecessary time away from

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sports or work. With an aging population and an increase in exercising participants who are aged $ 50 years,3 there will be an increased prevalence of osteoporotic stress fractures in the foot.8 This article reviews the literature, drawing on evidence from randomized controlled trials, nonrandomized intervention studies, observational studies, and consensus guidelines. An algorithm for the management of stress fractures for the foot is presented (Figure 1).


Sources and Selection Criteria

A search was conducted of Medline, Embase, and the Cochrane Library from their inception to January 2014 inclusive, using the search terms stress fracture, stress injury, stress reaction, exercise and osteoporosis, physical activity and osteoporosis, and exercise and post-menopausal. The search drew on the authors’ clinical experience.

The Unique Anatomy of the Foot

The foot is a unique structure, in that it has both flexible and nonflexible parts that act independently. The midfoot is relatively rigid at the midtarsal and the tarsometatarsal joints (TMTJ), providing stability between the hindfoot and midfoot. The midtarsal and TMTJ are effectively “fibrous” joints that provide stability of the midfoot preceding the

forefoot loading phase of the gait cycle. The 3 cuneiform bones form the true architectural arch. When standing, the foot is stabilized by the calcaneocuboid articulation and the relative immobility of the second and third TMTJ. This rigidity makes the second and third metatarsal bones prone to stress fractures.11 During typical walking, the foot is in contact with the ground 60% of the time, which decreases when running. As a result there are numerous risk factors causing stress fractures in the foot (Table 1), and there are specific biomechanical factors that place particular bones at risk (Table 2). In addition to normal anatomical characteristics, the foot is prone to congenital fusion or coalition, which further influences the distribution of forces within the foot, making stress fractures more likely.11 There are particular bones within the foot that are prone to delayed union or nonunion, as a result of poor blood supply and local biomechanics (Table 3). The forces throughout the foot are significant, with a force of 110% of body weight during heel strike, which increases to 250% during running.12 Furthermore, forefoot runners have forces through the foot and ankle that increase by 40% to 50% over the force in their heel striking counterparts.13 With the increasing incidence of vitamin D deficiency,9 and with low BMD being an independent risk

Figure 1. An algorithm for the diagnosis and management of foot stress injuries.

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Table 1. Risk Factors Causing Stress Fractures in the Foot

Table 3. Bones in the Foot That are Prone to Nonunion

Modifiable Risk Factors

Nonmodifiable Risk Factors

Low Risk of Nonunion

High Risk of Nonunion

Training regime Type of exercise Training surface Footwear and orthotics Fitness and experience Smoking Caffeine Alcohol Nutrition Body mass index Primary amenorrhoea Bone density

Bone anatomy Biomechanical factors Previous injuries Genetics Postmenopausal Age

Distal second to fifth metatarsal stress fractures Cuboid

Proximal second to fourth metatarsal Fifth metatarsal diaphyseal/ metaphyseal junction Navicular Talus Sesamoid Anterior process of the calcaneum

factor for stress fractures,10 understanding the complexity of foot stress fractures is crucial to avoid over- or undertreating this condition.

The Female Athlete

The assessment of BMD in females is essential to avoid missing underlying causative pathology. Tomczak and VanCourt8 found that 95% of their patient cohort had underlying osteopenia or osteoporosis. Both prospective and retrospective studies have shown that gender is not a risk factor in musculoskeletal injuries, except for stress fractures, where female sex is a risk factor.14,15 Adolescent runners are at high risk of stress fracture, as are older runners with their underlying deficiency in BMD.3 There are few prospective studies that assess the causes of stress fractures; nonetheless, a previous fracture is the most robust predictor of stress fractures in all age groups, and may guide future research and clinical care, in the management and prevention of stress fractures in runners of all ages.16 The increase in stress fractures in females is multifactorial. The presence of the female athlete triad or any of its Table 2. Anatomical Risk Factors for Foot Stress Fractures Navicular

Calcaneum Metatarsal

Short first metatarsal11 Underlying talonavicular osteoarthritis or joint stiffness14 Reduced ankle dorsiflexion11 Limited subtalar joint movement15 Metatarsus adductus11 Talar beaking15,16 Plantarward displacement of talonavicular joint11 Leg length discrepancy Calcaneonavicular coalition17 Elongated anterior process of the calcaneum100 Pes cavus/planus111 Metatarsus adductus89 Increase hindfoot inversion111

Cuneiform Calcaneum

components increases the athletes’ risk of stress fracture. Research has found that bone mineral density, menstrual irregularity or absence, and nutrition, known together as the female triad, all increase stress fracture risk. In addition, low body mass index (BMI) and increasing age all raise a women’s risk of suffering a stress fracture. As a result, the ”female triad” is actually a complex interaction among 5 factors and thus the phrase “female quintuple” may be more appropriate.3 The presence of the female quintuple or any of its components increases the risk of a stress fracture.3

Bone Mineral Density

Osteopenia and osteoporosis entail varying degrees of agerelated reductions in BMD. The BMD in postmenopausal women is related to either inadequate accumulation of bone at skeletal maturity or excessive loss with aging. Lower bone density is likely to be associated with an increased risk of stress fractures as shown by a cohort controlled study spanning premenopausal ages ranging from 18 to 45 years. The study was matched for age, sport, and weekly training volume, and found that the stress fracture group had significantly less trabecular BMD and cortical area.17 There is a heterogeneity of studies assessing exerciserelated bone changes in the literature. Borer18 reviewed the literature and concluded that the change in BMD in postmenopausal bones is very small. However, the reduction in the rate of BMD loss, or even modest gains in BMD as a result of exercise, may be of value in reducing osteoporosis. The subjects in studies that support exercise as a treatment for osteoporosis often have lower BMD than the reference population, thus resulting in inflated increases in BMD from the exercise regimes in the study.18 Adaptive responses require both dynamic mechanical stimulation19,20 and suprathreshold intensity.21,22 To avoid initiating stress fractures in postmenopausal women, careful implementation of activities is required with graded activity increases. This is especially true as cortical microstructure changes occur in women aged . 50 years.23 Stress fractures often


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start as an unicortical break in an area of relative weakness. Postmenopausal women may be more prone to stress fractures as a result of reduced BMD.24 Several other studies have not found a link between BMD and stress fractures, although these studies involve premenopausal women.25–28


Menstrual Irregularity

Tenforde et al16 found late menarche in 748 high school runners (age $ 15 years) to be an independent risk factor for stress fractures. Postmenopausal women by definition are amenorrheic. The decrease in estrogens associated with menopause contributes to the loss of bone and muscle mass.29–31 There are numerous causes of amenorrhea other than menopause, and they should be excluded. The following subsections discuss the causes of secondary amenorrhea and the absence of menses for $ 6 months (Table 4).

Nutrition

Nutrition is important in athletes, and female athletes have particular issues related to the “female triad.” Inadequate intake of calcium and vitamin D, or inadequate caloric intake, are associated with reduced bone mass.32 Decreased bone mass increases the strain on the remaining bone, increasing the fatigue fracture risk. Duckham et al33 found nutritional psychopathology was associated with an increased risk of stress fractures in endurance athletes, which may be associated with menstrual dysfunction and compulsive exercise. Although retrospective and cross-sectional studies have had mixed results, a prospective cohort study in premenopausal females found low-fat dairy products and the major nutrients in milk (calcium, vitamin D, and protein) were significantly associated with greater bone gains and a lower stress fracture rate.34 This is supported by a systematic review by Tenforde et al,35 who found prospective studies demonstrating that females who consumed $ 1500 mg of calcium daily exhibited the largest Table 4. Causes of Amenorrhea Contraception Pregnancy Hypothalamic failure Thyroid deficiency Polycystic ovarian syndrome Cushing’s syndrome Cervical stenosis and intrauterine adhesions Body mass index , 19 Sheehan’s disease Heroin abuse

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reduction in stress fracture injuries. Wentz et al36 found that drinking milk during the middle-school years positively correlated with hip BMD.36 In postmenopausal women, calcium supplementation with 500 to 1000 mg a day is ineffective,37,38 supporting the systematic review of Tenforde et al.35 Weight-bearing exercise alone does not provide protection against bone loss.39 However, estrogen replacement therapy is effective against bone mineral loss, and may actually increase total body BMD when combined with resistance exercise.40 Thus in postmenopausal women, the mechanical stresses of exercise may provide a necessary stimulus for increased skeletal incorporation of calcium, whereas the estrogenic effects on calcium facilitate bone mineralization. Vitamin D is produced by sunlight in the skin and is then converted to the active form (1,25-dihydroxycholecalciferol) in 2 stages. The first stage is carried out by the liver and the second by the kidney. Vitamin D increases calcium absorption in the gastrointestinal tract. A deficiency of vitamin D may lead to secondary hyperparathyroidism, which increases bone loss and possible stress fracture risk. Vitamin D deficiency has been found in some immigrant populations and in elderly institutionalized adults.41–43 However, deficiency is not uncommon in the general population,43 and gut malabsorption and medications such as anticonvulsants can contribute to a deficiency. Sonneville and colleagues44 compared dietary intake of calcium and vitamin D against the risk of stress fractures, and found that high vitamin D intake (rather than a high calcium intake) was protective against the development of stress fractures. The authors found a 50% reduction in the incidence of stress fractures in girls taking vitamin D who participated in a high-impact activity. Patients at high risk for stress fracture should be taught protective training techniques and informed about the potential benefits of supplementation with combined calcium and vitamin D. This is especially important if increased exercise is planned during winter or spring months, when vitamin D stores are at their lowest. Numerous recommendations have been made for the quantity of vitamin D required. Currently the Institute of Medicine guidelines suggest that 600 to 800 IU of vitamin D is necessary for adequate bone health in most adults. Recently McCabe et al45 recommend dosages up to 2000 IU, as vitamin D is safe and has a high therapeutic index and improves training efficiency. There is emerging evidence that vitamin D deficiency can have a profound detrimental effect on immunity, inflammation, and muscle function. Vitamin D status should be routinely



assessed so that athletes can be coached to maintain serum 25(OH)–vitamin D concentration of $ 30 ng/mL and preferably $ 40 ng/mL. The exact dosages are dependent on the athlete’s current vitamin D concentration, but should include regular safe sun exposure and dietary supplementation combined with increased vitamin D intake.46 A balanced calcium and vitamin D metabolism also appears to be of supreme clinical importance in the prevention of stress fractures in the elderly.47


Body Mass Index

Body weight is one of the strongest predictors of bone mass in people of all age groups,48 and body mass index (BMI) is a well-known predictor of fragility fracture.49,50 In a Finnish study with over 100 000 person/year followup, with a subject age range from 17 to 29 years, univariate analysis of subjects with a BMI of 20 to 25 kg/m2 showed that they had a significantly lower risk from stress fracture when compared with subjects with a BMI of , 20 kg/m2. This significance was lost, however, when multivariate analysis was conducted.51 Lower BMI has also been supported by Barrack et al52 to increase the risk of stress fractures in teenagers. The risk of stress fractures is further increased by the presence of oligomenorrhea or amenorrhea, elevated dietary restraint, or participation in a leanness sports exercise. A study assessing the impact of BMI on patients aged $ 40 years found that a BMI . 30 kg/m2 has a 2.6 relative risk of increased stress fracture compared with the population aged , 40 years .47

Age

The influence of age is up to 7-fold more important than is BMD alone.3 Breer et al47 concluded from their small, 105-patient series that the stress fracture risk was multifactorial, and age alone could not be linked to stress fracture risk independently. Other higher powered studies found that premenopausal stress fractures were twice as common in the 21- to 29-year age group compared with 17- to 19-yearolds.51 The largest sample of military recruits ever examined for stress fractures found that stress fracture risk increased from the age of 17 years at a rate of 2.2 and 3.9 cases/1000 recruits per year for men and women, respectively.53 Hormonal changes during menopause occur from the age of 50 to 55 years, causing a decrease in BMD. However, in a 6-year longitudinal study, aging was reported to be more important than menopause or bone status alone.31 The increased risk of stress fractures in the elderly population could be confounded by the reduced BMD and nutritional decline or from the lack of exercise found in this population.41,54

Classification of Stress Fractures

Stress fractures occur as a result of overuse injuries to bone, secondary to either bone fatigue or bone insufficiency. Fatigue stress fractures occur when normal bone is unable to resist excessive mechanical demands. Insufficiency stress fractures occur with normal strain on abnormal bone, caused by metabolic bone disease such as osteomalacia. Pathological fractures occur in weakened bone as a result of neoplasm or infection.55 There is no comprehensive classification system for stress fractures incorporating both clinical and radiographic characteristics that is applicable to all bones. The commonly available grading systems cited by Fredericson et al,56 Arendt et al,57 and more recently by Nattiv et al10 are not typically applicable to bones of the foot. Kaeding and Miller’s58 5-tier system grades stress fracture severity irrespective of image modality or location (Table 5). However, grade 3 stress fractures should be defined cautiously, as magnetic resonance imaging (MRI) and plain radiographs do not always correlate. There is a danger in under- or overestimating the severity of the stress fracture, if the underlying image modality is not known.10 The presence of a grade 3 or 4 fracture are managed differently depending on the degree of displacement and the bone involved (Table 3).

How Are Stress Fractures Diagnosed? History

Patients with a stress fracture usually complain of pain localized to a particular bone of the foot; the pain starts progressively earlier in each training session and gradually gets worse. Eventually pain is felt during normal daily activities, suggesting a progressive injury. Identifying the precise location of the pain is important for the radiologist to be able to interpret the scans. The athlete should be asked about the nature of the training regimen, specifically about recent excessive or sudden increases in training, or a lack of rest days. Risk factors for bony stress injury should be identified Table 5. Kaeding and Miller’s58 5-Tier Grading System Grade of Stress Fracture

Radiographic Findings

1 2 3 4 5

Asymptomatic radiographic findings Pain with no fracture on imaging Non displaced fracture on imaging Displaced fracture on imaging Sclerotic nonunion on imaging

Reprinted from Journal of Bone and Joint Surgery (American),Volume 95, Kaeding CC and Miller T. The comprehensive description of stress fractures: a new classification system, 1214–1220, Copyright 2013, with permission from Rockwater, Inc.58


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as listed in Table 1. Military recruits and female athletes should be questioned regarding dietary intake, menstrual pattern, and personal or family history of stress fractures. Clinical suspicion based on the history and the associated risk factors is of primary clinical importance for making the correct diagnosis, followed by appropriate imaging investigations. Schneiders et al,59 in a systematic meta-analysis of the literature, found poor sensitivity and specificity for the use of a tuning fork as an examination technique for diagnosing stress fractures.

Imaging Techniques Plain Radiograph

Plain radiographs are relatively easy to perform and inexpensive. If a fracture is present on this modality, then it is diagnostic (Figure 2). X-ray sensitivity at the initial presentation is poor (15%–35%), increasing to 30% to 70% on follow-up images due to the presence of periosteal changes.5 A radiograph may appear normal for 3 months or even longer from symptom onset, and thus a negative radiograph would warrant further investigations if symptoms are suggestive of a stress fracture.60 Contrary to the description by Adendt et al,57 periosteal reaction does not correlate with the severity of MRI findings.10 Further imaging is essential for talar and navicular fractures, as both are prone to avascular necrosis. Identifying the site and extent of the fracture aids operative planning.4

Isotope Bone Scan With the high sensitivity of isotope bone scans, some authors define stress fractures as a positive scan result.61 Although a negative bone scan excludes a stress fracture, a positive scan is nonspecific. Increased isotope uptake is seen in any condition with increased bone turnover, such as infection, cancers, and rheumatologic inflammatory conditions (Figure 3). Thus, we would not recommend the routine use of this imaging technique.

Magnetic Resonance Imaging Magnetic resonance imaging has a sensitivity of up to 99% for stress fractures62 and is also specific. It entails no radiation exposure and has the advantages over plain radiography of being able to identifying changes often weeks earlier and excludes soft tissue differentials.63 Magnetic resonance imaging may also be useful in identifying resolution of fractures.64 Magnetic resonance imaging is able to identify fractures early in the clinical presentation, allowing the clinician to intervene earlier in the clinical course.65 Earlier intervention will reduce the time away from activity participation. Magnetic resonance imaging, in addition to plain radiography, can be used to grade the severity of fractures. Arendt and Griffiths66 recommend increased rest time for fractures with increased severity. The classification system for stress fractures has been simplified further by Nattiv et al,10 who

Figure 2. A healing second metatarsal stress fracture.

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The Pathophysiology, Diagnosis, and Management of Foot Stress Fractures Figure 3. High signal uptake of a third metatarsal bone. Due to the lower specificity of bone scans, the differentials include infection, cancer, and a stress fracture.

but early evidence suggests it may play a role in the diagnosis of easily accessible fractures, such as the metatarsal bones. Thus ultrasound may be an alternative to MRI,69 but further research is needed.


Therapeutic Ultrasound In a recent study (level 2), therapeutic ultrasound was used as a primary evaluation tool of bone stress injuries in 113 elite track and field athletes. It had 81.8% sensitivity, 66.6% specificity, 99% positive predictive value, 13.4% negative predictive value, and 81.4% accuracy. The study authors concluded that therapeutic ultrasound is a reproducible procedure that is sufficiently reliable to diagnose bone stress injuries.70

Prevention and Treatment

described the presence of a fracture line on either T1- or T2-weighted MRI. Immobilization or early surgical intervention is recommended if this occurs at a site prone to nonunion (Table 3) or in the presence of low BMD.

Computed Tomography Computed tomography (CT) is useful in the presence of a fracture evident on T1- or T2-weighted MRI. It is especially useful in bones that are prone to avascular necrosis or when assessing evidence of delayed union in high-risk fractures (Table 3),67 or if malignancy, osteomyelitis, or Brodie’s abscess are suspected. The sensitivity of CT is lower than that of an isotope bone scan, but CT is more specific and has an added advantage over MRI in patients who are claustrophobic.68

Ultrasound The usefulness of ultrasound for foot stress fractures is still undergoing clinical review. It is highly operator dependent,

The periodization training method optimizes gains in performance while minimizing the risk of developing a stress fracture. Periodization involves increasing training over a 3-week cycle followed by a week of relative rest, which enables subsequent metabolic adaptation to occur. Periodization was first introduced into the training of military recruits when stress fractures were noted to be frequent. Incorporation of rest days almost halved the number of stress fractures among Royal Marine trainees from 7% to 3.8%.71 Foot stress fractures with a low risk of nonunion (Table 3) and bones with normal BMD can be managed conservatively using a graded protocol based on the degree of symptoms and the underlying MRI grade. The first stage involves analgesic control, avoiding the use of nonsteroidal anti-inflammatory drugs because they may have adverse effects on bone healing.72 Weight bearing is allowed as long as the athlete remains pain free, which can be addressed with crutches, heel weight bearing, or synthetic or air-based Velcro walking boots. Aerobic training is maintained using cycling, swimming, and deep water running. Endurance athletes can experience a 7% decline in maximum oxygen consumption (VO2max) within 2 to 3 weeks after cessation of training.73 Deep water running allows the natural buoyancy of the body to reduce the weight of the submerged limb, while maintaining cardiovascular and neuromuscular function.74,75 Antigravity treadmill running has all the same advantages as deep water running, but with lower limb weight support there will be less metabolic demand.76 When the athlete first returns to running and other activities, it should be at a low intensity. Only after the athlete has been consistently pain free in daily activities and fully weight bearing for 2 weeks can training resume. The athlete



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returning to running should adhere to the 30:10 rule77: the athlete starts running at a third of the normal pace and for a third of the typical weekly distance, with rest days and periodization incorporated. This is then increased by weekly 10% increments.78 Any return of symptoms should warrant careful assessment of the rehabilitation program and return to the previous pain-free level. High-risk stress fractures require different management. Nattiv et al10 showed that the presence of a fracture line on MRI T1 or T2 sequences was of prognostic value. The absence of a fracture line on MRI usually indicates that healing will occur with nonoperative management, including weight-bearing restriction and immobilization that is based on the location of the fracture.79 These factors must be closely assessed to confirm complete healing before the athlete returns to play. The presence of a fracture line and low BMD are significant and independent risk factors for return to sports.10 Furthermore, the presence of oligomenorrhea or amenorrhea in females is associated with a delay in seeking medical help for a stress fracture, which results in the initial presentation at higher stress fracture grades.10 A simple screening tool can also be used in the assessment of individuals who are at risk of stress fracture. Cowan et al80 assessed . 1500 female army recruits, and found patient failure to complete a 5-minute step test increased stress fracture incidence by 76%. Although this test is likely to assess underlying fitness, it is not known if this assessment is transferable to male military personal or to athletes.

Orthotic Devices

Orthotic devices are thought by many investigators to prevent lower-extremity stress fractures by absorbing shock and altering biomechanics, but this remains controversial. Most data related to the effects of orthotics on stress fractures are from studies on the prevention of stress fractures and lower extremity soft tissue injuries in military recruits undergoing military induction training. In a Cochrane database systematic review in 2000, Gillespie and Grant81 examined 12 studies of military recruits in 3 countries and concluded that the use of shock-absorbing insoles in military boots was effective in stress fracture prevention. Rome et al82 re-evaluated this issue in a 2005 update and concluded that orthotics were “probably” effective in reducing the incidence of stress fractures in military personnel. In a recent 2-arm feasibility study, Baxter et al83 evaluated the effects of orthotics on lowerextremity soft tissue injuries in New Zealand army recruits by screening for subjects with a biomechanical abnormality. They found a reduction in the incidence of stress fractures of 94

the foot and tibia. In a randomized controlled trial, Mattila et al84 evaluated the incidence of lower-extremity injuries (including stress fractures) in Finland Army recruits. They studied the impact of wearing combat boots with orthotics over a 6-month period. They found that orthotic devices were not effective in preventing lower extremity stress fractures. Further studies of this topic are needed.

Metatarsal Fractures

The majority of metatarsal fractures occur in the distal second to fifth metatarsal, which are usually undisplaced and can be managed conservatively with a stiff-soled shoe or a walking boot. High-risk fractures with a high rate of nonunion include the proximal second to fifth metatarsal fractures; the incidence of nonunion reported in the literature ranges from 20% to 67%.85,86 Opinions about the management of these fractures are divided. Some authors recommend that nonsclerotic fractures of the fifth metatarsal be treated conservatively with a non–weight-bearing cast for 6 to 8 weeks, but operative intervention is required if there is any sign of sclerosis on imaging. Operative intervention includes medullary curettage and bone grafting followed by non–weight bearing for 6 weeks.87 Intramedullary screw fixation has achieved a 100% union rate in 22 patients at 8 weeks with an earlier return to activities, albeit with a complication rate of 9%.88 After surgical treatment and confirmation of radiographic union, an athlete should use an orthotic during the first season of play.78 Rongstad et al89 surgically managed 11 proximal fourth metatarsal stress fractures with plate fixation and calcaneal autograft over a 13-year period. The patients returned to sports at an average of 12 weeks, and an improvement in American Orthopaedic Foot and Ankle Society (AOFAS) score was seen from 55 preoperatively to 94 postoperatively. This was a not a case-control series and it is not known if these athletes’ injury would have gone on to union anyway. However, the average time from diagnosis until surgery was 3 months in 10 patients and . 2 years in 1 patient. This suggests a lengthy period of initial conservative management. Further surgery was subsequently required in 2 of the 11 patients (18%) for metal work removal, and there was 1 neuroma, which was managed conservatively. A case report by Watson et al90 described the successful conservative management of a proximal second metatarsal stress fracture in a 15-year-old dancer, an age at which better bone adaptation and healing occur, yielding a better prognosis than typically is seen with this stress fracture. But the patient had a significant risk factor: menarche delayed until



the age of 15. Ballet dancers are particularly prone to stress fractures at the proximal aspect of the second metatarsal due to dancing in the “en pointe” position. The presence of the Lisfranc joint and ligamentous involvement warrants non– weight-bearing immobilization for $ 4 weeks with stress fractures around the second metatarsal base.91,92

Figure 4. A calcaneal stress fracture on a T2-weighted magnetic resonance imaging scan.


Cuboid Fractures

Cuboid stress fractures are rare. In a 19-year retrospective review in 1 institution, 10 cases were found, 9 of whom were in women.93 The authors concluded that age-related bone loss and plantar fascia dysfunction were likely contributing factors. With the rarity of this condition there may be more contributing factors that are currently unknown. Other risk factors might include pes cavus or hindfoot inversion placing more pressure on the lateral side of the foot. Conservative management is used to offload the lateral foot with either a walking boot or cast.

Cuneiform Fractures

The rarity of cuneiform stress fractures has been limited to case reports.94,95 The risk factors postulated in the literature have been the propulsive phase of running,94 and, in larger case series, concurrent plantar fasciitis.96 It is difficult to conclude if one is the result of the other. However, both these conditions may share the same etiological factors such as being overweight and being older.97 Conservative management to relieve the symptoms with either a walking boot or cast is recommended.

Calcaneal Fractures

Calcaneal stress fractures are found typically in jumping sports and activities. They can be mistaken for retrocalcaneal bursitis, Achilles tendinopathy, plantar nerve entrapment, subtalar joint arthritis, radiculopathy, plantar fasciitis, or aggravation of rheumatological conditions.98 Calcaneal stress fractures (Figure 4) are managed in athletes on an individual basis using either partial weight bearing or non–weight bearing to relieve the underlying pain. The anterior process of the calcaneum (APC) is much less frequently involved, with only 3 stress fractures being reported in the literature. Only 1 case did not have an associated tarsal coalition.99 An elongated APC has also been reported as a risk factor for such stress fractures, and represents an incomplete coalition.100 The APC is the anterolateral prominence of the calcaneum articulating with talus superiorly and cuboid anteriorly, and the ligamentous origin of the bifurcate ligament. As a result of the complex

anatomical relationship and typically because of significant pain, a cautious conservative approach should be adopted.101 A non–weight-bearing cast should be used for 6 weeks. Taketomi et al99 reported that failed inadequate conservative measures resulted in nonunion; 1.5-mm Kirschner wires were used to drill the nonunion under image control, resulting in successful clinical union at 6 weeks and a return to graduated running at 8 weeks.

Navicular Fractures

Navicular fractures are particularly evident in basketball players and runners,11 and there may be an association with talonavicular arthritis.102 The navicular bone is covered on 3 sides by articular cartilage, and there is only a small area for the blood supply to enter. This results in an area of relative avascularity in the central third, an area prone to stress fractures.103,104 As a result, appropriate imaging is essential for correct management. An MRI scan has the highest sensitivity for diagnosis of a stress fracture; however, a CT scan in navicular fractures (Figure 5) guides further management. Saxena et al105 have created a CT radiographic classification system that describes the severity of the stress fracture. Type 1 involves the cortex only and types 2 and 3 involve the navicular body and distal cortex. In a prospective series, type 2 and 3 navicular stress fractures with evidence of avascular necrosis or cystic or sclerotic changes were prone to delayed union, and early surgical treatment was recommended. Returning to sports typically occurs at 4 months. Conservatively managed navicular stress fractures must be with strict non–weight bearing for $ 6 weeks. The risk of


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Figure 5. A computed tomography scan with a right navicular fracture.

nonunion may be as high as 74% in those managed with activity modification only.106,107

Talar Fractures

Talar fractures are rare in the literature, with an incidence in the military of 4.4/10 000 person-years, with two thirds occurring in the talar head.108 Other case reports in athletes suggest that axial loading and plantar flexion of the ankle may cause repetitive microtrauma and resultant stress fracture.109 Talar stress fractures rarely occur in the talar neck, but these must be carefully assessed. The talar sinus has a tenuous blood supply from a branch of the posterior tibial artery. A stress fracture to the talar neck has the potential to disrupt this supply and cause avascular necrosis to the talar body. From our experience, CT scan enables accurate osseous assessment of these fractures. Non–weight bearing must be continued for a minimum of 6 weeks or until there is evidence of both clinical and radiographic union. Sormaala et al108 noticed radiographic joint degeneration associated with talar fractures; thus, the significance of talar neck fracture should not be underestimated. As a result, 4 to 6 weeks of protected weight bearing in a cast or boot after the initial 6 weeks of non–weight bearing is recommended.

Sesamoid Fractures

Sesamoid stress fracture should not be mistaken for a bipartite sesamoid. Axial radiographs of the sesamoid are helpful (Figure 6), but the most useful diagnostic investigation is an MRI scan, which can differentiate a fracture from a bipartite sesamoid and can identify evidence of nonunion or avascular necrosis. Off-loading the sesamoid with a 96

non–weight-bearing cast and avoiding toe dorsiflexion are advocated for 6 weeks.78 Although steroid injections should be avoided in new fractures, their use as a diagnostic and therapeutic treatment in the chronic sequelae of sesamoid fractures can be considered in order to avoid surgical excision. Excision should be used only as a last result, as it can lead to a number of subsequent complications such as hallux abductus.110 However, in order to maintain push-off strength in the athlete, internal fixation could be considered, although adequate-sized studies are not available to predict union rates and outcomes.

Conclusion

Stress fractures of the foot require careful assessment and management. The foot is anatomically complex, with intricate biomechanics that are still not entirely understood. As a result, the etiology of foot stress fractures is complex and multifactorial. The intrinsic factors that are involved include mechanical factors, such as bone density, skeletal malalignment, body size, and composition; physiological factors, such as bone turnover rate, flexibility, and muscular strength and endurance; as well as age, hormonal and nutritional factors. The extrinsic risk factors include training surface, footwear, orthotics, training errors, and overloading. The diagnosis of stress fracture of the foot is not always easy to make and requires a high level of suspicion, as radiographs are often unremarkable at the onset of a stress fracture. There are many radiological imaging modalities available, but MRI and CT scans are found to be the most reliable in identifying and confirming stress fractures of the foot. Identifying underlying BMD deficiency and the bone involved will allow appropriate immobilization and treatment of any underlying metabolic bone disease. The presence of any




Figure 6. An axial sesamoid view with an underlying stress fracture.

one of the female quintuple requires further BMD assessment. Once management of the underlying bone pathology has been assessed, the high-risk fractures are managed with non–weight bearing pending the results of imaging. Low-risk stress fractures are managed clinically, depending on how symptomatic the patient is during daily activities or exercise.

Conflict of Interest Statement

James Pegrum, MB BS (Lon), BSc (Orthopaedics), MSc (Sports Medicine), MRCS (Eng), Diploma DMM UIAA, Vivek Dixit, MSc, M.PhiL, M.HSc (Public Health), PhD (Med), CAFÉ, PDCR, FASc (ASAW), FRSH, FHTA, Nat Padhiar, MSc, PhD, FCPodS FFPM RCPS (Glas), and Ian Nugent, MB, BS, FRCS, have no conflicts of interest to declare.

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