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All articles published in the Journal of Special Operations Medicine are protected by United States copyright law and may not be reproduced, distributed, transmitted, displayed, or otherwise published without the prior written permission of Breakaway Media, LLC. Contact [email protected].

An Ongoing Series

Stress Fractures Etiology, Epidemiology, Diagnosis, Treatment, and Prevention

Joseph J. Knapik, ScD; Katy Reynolds, MD; Kyle L. Hoedebecke, MD

ABSTRACT

Stress fractures are part of a continuum of changes in Keywords: ; risk factors; diagnosis; treatment healthy in response to repeated mechanical defor- mation from physical activity. If the activity produces excessive repetitive stress, osteoclastic processes in the Introduction may proceed at a faster pace than osteoblastic processes, thus weakening the bone and augmenting Stress fractures are part of a continuum of changes in the susceptibility to stress fractures. Overall stress fracture bone in response to mechanical stress. The continuum incidence is about three cases per 1,000 in active duty spans events from normal bone remodeling to a frank Servicemembers, but it is much higher among Army ba- fracture. Figure 1 is a summary of terms used to describe sic trainees: 19 per 1,000 for men and 80 per 1,000 for this spectrum, obtained from a review of various terms women. Well-documented risk factors include female used in the literature1–4 and clinical experience. The term sex, white ethnicity, older age, taller stature, lower aero- “stress reactions” has been used to identify conditions bic fitness, prior physical inactivity, greater amounts of where early changes occur in the bone and the Soldier current physical training, thinner bones, cigarette smok- experiences pain symptoms, but there is no evidence of ing, and inadequate intake of vitamin D and/or calcium. bone lesions on imaging. Stress fractures usually refer to Individuals with stress fractures present with focal ten- conditions where there are distinct partial or incomplete derness and local pain that is aggravated by physical fracture lines on imaging. The term “bone stress injury” activity and reduced by rest. A sudden increase in the has been used to refer to the portion of the continuum volume of physical activity along with other risk factors (Figure 1) encompassing both stress reactions and stress is often reported. Simple clinical tests can assist in diag- fractures. nosis, but more definitive imaging tests will eventually need to be conducted if a stress fracture is suspected. Figure 1 Spectrum of bone changes in response to repetitive stress. Plain radiographs are recommended as the initial im- aging test, but magnetic resonance imaging has higher Bone Stress Injury sensitivity and is more likely to detect the injury sooner. Normal Bone Stress Stress Frank Treatment involves first determining if the stress frac- Remodeling Reaction Fracture Fracture ture is of higher or lower risk; these are distinguished by anatomical location and whether the bone is loaded in Increasing Physical Damage tension (high risk) or compression (lower risk). Lower- risk stress fractures can be initially treated by reduc- ing loading on the injured bone through a reduction in Bone stress injuries are typically associated with ha- activity or by substituting other activities. Higher-risk bitual mechanical deformation of the bone. The injury stress fractures should be referred to an orthopedist. In- generally occurs in individuals with otherwise healthy vestigated prevention strategies include modifications to bones, often in association with unaccustomed but re- physical training programs, use of shock absorbing in- petitive physical activity.5–8 This type of fracture is often soles, vitamin D and calcium supplementation, modifi- referred to as a “fatigue fracture” and is to be distin- cations of military equipment, and leadership education guished from “insufficiency fractures,” which are par- with injury surveillance. tial or incomplete bone ruptures due to loading on bone

120 All articles published in the Journal of Special Operations Medicine are protected by United States copyright law and may not be reproduced, distributed, transmitted, displayed, or otherwise published without the prior written permission of Breakaway Media, LLC. Contact [email protected]. that has become osteopenic with aging or disease (e.g., hypervitaminosis A, sarcoma). Insufficiency fractures may occur spontaneously in association with normal loading or minimal trauma that would not result in a fracture in healthy bones.9–14

Soldiers involved in heavy physical activity may be at risk for stress fractures, especially if the activity involves sudden increase in frequency, duration, or intensity. Re- Figure 2 Structure of a covery times can be extended, negatively affecting both long bone. Soldier and unit effectiveness for a considerable time.15–18 This article covers the etiology, epidemiology, diagnosis, treatment, and prevention of fatigue fractures, which will hereafter be referred to as stress fractures.

Etiology Bone will bend when subjected to impact forces induced Obtained from https://commons.wikimedia.org/wiki/File:Structure_of by activities like running or marching with loads. _a_Long_Bone.png They will return to their original configuration when the impact forces are reduced or removed. The repetitive 2007 reported incidences of 19 cases per 1,000 Service- bending results in an increase in cyclic hydrostatic pres- members (SMs) for men and 80 cases per 1,000 SMs sures that are sensed by osteocytes within the bone ma- for women.28 The incidence among active duty military trix. Mechanical pressures stimulate osteocyte-directed personnel from 2003 to 2012 was 2.7 cases per 1,000 transcription of osteoclasts, which begin the bone remod- SMs.29 During the Central Burma campaign in the Sec- eling process. If the repetitive mechanical stress is applied ond World War, 80 stress fracture cases were reported gradually over time (i.e., progressive overload), normal in one 7,000-man infantry unit (1.1% incidence) during bone remodeling occurs. That is, osteoclastic processes, a long road march.33,34 Early in the study of this injury, which resorb bone, approximately balance osteoblastic stress fractures were termed “march fracture” because processes, which form new bone. However, if the repeti- Soldiers would often present with this injury after road tive stress is applied in a relatively short time, as with a marching35–38; however, cases emerged in which the on- long foot march with a heavy load for which the Soldier set was insidious and the injury could not be linked to has not sufficiently trained, osteoclastic processes may a single event.35,37,39 Breithaupt is credited with the first proceed at a faster pace than osteoblastic processes. This description of the condition in Prussian Army Soldiers.37 imbalance produces a vulnerable period when the bone is During the Second World War, cases and case series be- weakened and susceptible to rupture.5,19,20 gan to appear in the literature in both British35,39 and American33 36–38,40 military training. Stress fractures appear more likely to occur where bone remodeling is slower. Areas of slow remodeling include We obtained data on ambulatory (outpatient) stress frac- compact (cortical) bone, the long bone diaphysis (Figure tures directly from the Defense Medical Epidemiology 2), and bodies of cuboid-shaped bones like the vertebrae, Database (http://www.health.mil/Military-Health-Topics tarsals, and carpals. In spongy (cancellous) bone where /Health-Readiness/Armed-Forces-Health-Surveillance- more active remodeling occurs, there is a lower likeli- Branch/Data-Management-and-Technical-Support/ hood of stress fractures. Cancellous bone is contained Defense-Medical-Epidemiology-Database) for the Army, in the metaphysis and epiphysis of both long and square Navy, Marine Corps, and Air Force. The data were visits bones (Figure 2). Cancellous bone has a metabolic turn- to medical care providers with International Classification over rate eight times faster than cortical bone.3,4,12,21 of Diseases, Ninth Revision codes of 733.93 to 733.98 (the codes for stress fractures at various anatomical loca- tions), diagnosed from 2006 through 2014. The overall Epidemiology rate was 17.3 visits per 1,000 SMs. Data by year, sex, age, and military service are shown in Figure 3. Rates tended Incidence to decrease in the period examined (Figure 3A). Military Stress fractures are a commonly encountered injury in Servicewomen had 3.6 times the stress fracture rate of athletics, among military recruits22–29 and among trained military Servicemen (Figure 3B) and rates decreased with military personnel.29–32 A study that examined the ­entire age (Figure 3C). The Marine Corps and Army had the population of US Army basic trainees from 1997 to highest rates and the Navy had the lowest (Figure 3D).

Stress Fractures 121 All articles published in the Journal of Special Operations Medicine are protected by United States copyright law and may not be reproduced, distributed, transmitted, displayed, or otherwise published without the prior written permission of Breakaway Media, LLC. Contact [email protected].

Figure 3 Rates and factors associated with stress fractures bone section modulus and a lower bone strength index in US military personnel. (A) Rates from 2006 to 2015. (ratio of section modulus to bone length) than men.63 (B) Association with sex. (C) Association with age. Female bones are thinner and narrower, which provides (D) Association with military service. AF, Air Force; MC, less bone strength.63,64 With regard to anatomical dif- Marine Corps. ferences, women have wider pelves,80 which result in a varus tilt of the hip and a larger bicondylar angle,81 which places greater stresses on the hips and lateral as- pects of the knee and lower leg during physical activ- ity. Both men and women with wider pelves have higher stress fracture incidence, suggesting that a wider pelvis alone (regardless of sex) increases injury risk.63

The association between age and stress fractures may be related to changes in bone with aging. Bone mass declines with age, primarily in the spongy bone com- partments. Losses in spongy mass in the distal tibia amounted to 0.24% per year and 0.40% per year for men and women, respectively, in one study.82 This loss may be due to a reduction in the number of osteoblastic stem cells or a reduction in the lifespan of the osteo- blasts themselves. The overall loss of bone mass with age would affect bone strength, and age-related effects The reason for the decrease over years is not clear, but on osteoblasts would result in slower bone remodeling, there have been considerable efforts to reduce the in- thus increasing susceptibility to activity-induced stress cidence of stress fractures and other injuries at many fractures. However, as mentioned, most stress fractures basic training sites.41–43 The higher rate in younger SMs manifest in the cortical (compact) bone. In this compart- may be due to the larger number of military recruits in ment, there are age-related changes in the mechanical these younger groups: one study of military stress frac- properties of the collagen network (upon which bone tures showed that most of these occurred in military re- minerals deposit), which reduce strength, modulus, cruits, with an incidence of 40 cases per 1,000 recruits, and ability to absorb energy, while increases in bone compared with three cases per 1,000 active duty SMs.29 porosity reduces bone stiffness and strength.83,84 These Also, older SMs tend to be in administrative and/or su- changes likely contribute to the higher age-related stress pervisory positions and may perform less heavy physical fracture risk. activity. There is higher stress fracture risk among those of white Risk Factors ethnicity and lower risk among those of black ethnicity. Considerable research has been conducted to identify fac- This could be partly related to the higher bone mineral tors that increase stress fracture risk. Well-documented density (BMD) in blacks compared with other racial/eth- risk factors include female sex,2,22,27,44–49 white ethnic- nic groups.85–87 This difference persists after adjustments ity,2,22,49–54 older age,2,22,49,50,52,54,55 taller stature,25,49,56 lower for body composition, dietary history, sun exposure, aerobic fitness,47,54,55,57–59 prior physical inactivity,25,50,54,55 biochemical bone markers, lifestyle characteristics, and greater amounts of current physical training,24,60–62, thin- other factors.88 In addition to higher BMD, studies of ner bones,63–65 cigarette smoking,55,66,67 and inadequate the female femur have shown that there are differences intake of vitamin D and/or calcium.55,68–70 Risk factors in bone geometric properties between black women and with limited support include high foot arches,71,72 older white women: black women have longer and narrower running shoes,50 genu varus,73 irregular menses,55,59 femora with thicker cortical areas and smaller medullary limb-length discrepancies,74 and particular movement areas. These factors increase mechanical strength by con- patterns.75,76 tributing to lower bending stresses in the cortical areas during physical activity.87 The higher BMD and the man- The sex difference in stress fracture risk may be related ner in which the bone architecture is arranged may con- to fitness levels, bone characteristics, and/or anatomy. tribute to the lower stress fracture incidence in blacks. Women have lower average fitness levels than men and lower fitness is associated with higher overall injury The length of long bones in the lower body (i.e., femur, rates58,77 as well as a higher incidence of stress frac- tibia, fibula) is highly related to height, with correla- tures.47,56,59,63,78 In the bones of the lower body, where tions in the range of 0.9.89,90 Taller individuals with pre- most stress fractures occur,22,78,79 women have a lower sumably longer bones may experience more bending

122 Journal of Special Operations Medicine Volume 17, Edition 2/Summer 2017 All articles published in the Journal of Special Operations Medicine are protected by United States copyright law and may not be reproduced, distributed, transmitted, displayed, or otherwise published without the prior written permission of Breakaway Media, LLC. Contact [email protected]. and strain on their lower-body long bones during physi- Other clinical tests that have not been specifically evalu- cal activity. One study63 showed that men with stress ated for sensitivity but are often used in suspected stress fractures had longer femora compared with those with- fracture cases include the hop and fulcrum tests. For out stress fractures, and the longer bones contributed to the hop test,99,100 the individual hops on the affected lower bone strength. leg and localized pain is assumed to indicate a positive test. The fulcrum test101 is used for suspected femoral Prior physical activity may reduce stress fracture risk stress fractures. The patient is seated on the examination during current activity, because of changes in bone tis- table with lower legs dangling off the table. The evalu- sue induced by the prior activity. Physical activity, es- ator places one of his under the affected thigh and pecially activities involving high impact forces (e.g., with the other pushes down on the distal femur. running, soccer, basketball, gymnastics) increase bone Increasing pressure on distal femur produces increasing mineral content, BMD, bone size, bone mass, and re- discomfort, pain, and apprehension. The unaffected leg sult in activity-specific bone remodeling.91–93 Effects of serves as a control. physical activity may be larger in men than in women and the maintenance of physical activity appears to be Although useful for an initial evaluation, clinical ex- important for the maintenance of bone mass.93 aminations are generally not sufficient for the diagnosis of stress fractures because the results of tests can vary depending on the stage of the injury on the pathologi- Clinical Evaluation and Diagnosis cal spectrum (Figure 1). Imaging studies should be con- Individuals with stress fractures present with localized ducted when clinical evaluation provides suspicion of a pain that is aggravated by physical activity and reduced stress fracture. Imaging tests include plain radiographs, by rest. Focal tenderness is present in most cases; swell- bone scans, and magnetic resonance imaging (MRI). ing and erythema may be present. Patient history notes Plain radiographs have a high initial incidence of false- a recent increase in the frequency, duration, or intensity negative results because the injury is generally not evi- of physical activity. Simple clinical tests may be use- dent on radiographs until 2 to 4 weeks after the onset ful in the initial diagnosis, but more definitive imaging of pain. Bone scans can produce many false-positive re- tests will eventually need to be conducted if stress frac- sults. Despite the cost, MRI may be the most useful test tures are suspected. The potential risk factors noted in because it may detect stress fracture-related abnormali- the previous section should be considered in the overall ties within 1 to 2 days of the injury.13,102–106 A systematic evaluation. review of high-quality studies evaluating MRI found sensitivities of 68% to 99% and specificities of 92% to Simple clinical tests include the tuning fork test, patel- 84%.107 With MRI, the low rate of false-negative results lar-pubic percussion test, hop test, and the fulcrum test; may reduce the need for additional testing.107 Nonethe- however, only the two former tests have been evalu- less, plain radiographs are a low-cost option and are ated for their ability to detecting stress fractures. For recommended as an initial imaging test by the Ameri- the tuning fork test, the Soldier is supine and a vibrat- can College of Radiology.108 In the case of Soldiers who ing 128hz tuning fork is applied to and moved along must perform high-risk physical activity that may exac- the boney surface. Pain during tuning fork application erbate symptoms or the stress fracture itself, a negative is considered a positive sign. At least three studies94–96 finding on plain should be confirmed with have compared the tuning fork test (i.e., pain exacerba- MRI.107,108 tion on application of the tuning fork) to bone scans (primarily tibia and fibula but also foot bones) and In a setting with limited diagnostic ability (e.g., deploy- found sensitivities (i.e., ability to correctly identify a ment in isolated areas), a presumptive diagnosis can be stress fracture) ranging from 71% to 80% and specifici- provided without radiographic imaging when multiple ties (i.e., ability to detect those without stress fractures) risk factors and findings on physical examination for ranging from 60% to 67%. The patellar-pubic percus- stress fractures are present. However, imaging is always sion test was developed to assess hip fractures. With the recommended for high-risk stress fractures or if the pa- Soldier supine, the evaluator listens with a stethoscope tient’s symptoms do not improve. Referral to higher lev- at the pubic symphysis of the affected side while tap- els of medical care should be considered in these cases. ping on one patella and then the other. Similar sounds indicate a lower likelihood of a fracture, but if the bone Treatment is disrupted, the sound on one side will be diminished in pitch and loudness compared to the other side. Two It is important to distinguish between stress fractures studies97,98 examining the accuracy of this test for detec- that are at high risk for nonunion versus those that will tion of hip fractures found sensitivities of 79% and 96% heal with a lower risk of complications. Clinical experi- and specificities of 86% and 95%. ence suggests that stress fractures can be stratified into

Stress Fractures 123 All articles published in the Journal of Special Operations Medicine are protected by United States copyright law and may not be reproduced, distributed, transmitted, displayed, or otherwise published without the prior written permission of Breakaway Media, LLC. Contact [email protected]. high-, medium-, and low-risk categories based on ana- extremities16,22,27,113,114 and the Soldier may be put on tomical location. This classification is based on how the crutches to reduce weight bearing on the lower extremi- bone is loaded: in tension or compression. Anatomical ties. Casting to immobilize the bone should be consid- sites loaded in tension have a high risk of nonunion, a ered. Surgical fixation may be required in some cases higher likelihood of progressing to a frank fracture, and that do not respond to conservative treatment. a higher risk of recurrence. Sites loaded in compression appear to have lower risk. Stratification of anatomical Ultrasound has been suggested as a possible modality sites into high, medium, and low risk is shown in Table for reducing fracture healing time.111 A 2009 a system- 1.12,13,21,109,110 atic review of 13 randomized controlled trials studies found that the quality of published studies was low and Table 1 Stress Fracture Anatomical Sites Stratified on Risk of results conflicting; the authors suggested a large double- Nonunion12,13,21,110 blind study.115 Such a study was conducted from 2008 High Risk Medium Risk Low Risk to 2012. That study involved 501 patients with tibial fracture in 43 medical centers with 1 year of follow-up. Femoral neck Pelvis Fibula Low-intensity pulsed ultrasound after surgical fixation Anterior mid- Femoral shaft Lateral malleolus of the tibia did not improve functional recovery or ra- tibia diographic evidence of healing.116 Navicular (body) Posterior or Calcaneus medial tibia Bisphosphonates (e.g., pamidronate, ibandronate) have Talus Medial Cuboid been effectively used in the treatment of .117 a malleolus These compounds act by reducing osteoclastic activity Proximal fifth Proximal fifth Cuneiforms while allowing osteoblastic activity to proceed; they metatarsal metatarsal thus favor bone formation.118,119 Preliminary work with Hallux sesamoids Second through fourth these compounds suggested that intravenous injections metatarsals shafts may accelerate healing of stress fractures,120,121 although Pars Longitudinal patella there have been no double-blind randomized trials to interarticularis date on stress fractures. A recent systematic review of 27 Transverse patella randomized controlled trials reported that bisphospho- nates had beneficial effects on insufficiency fractures.122 aSome clinicians place this in the high-risk group. Low- to medium-risk stress fractures can be initially treated by reducing loading on the injured bone through Prevention a reduction in activity. This allows healing processes to A number of interventions have been tested to reduce the proceed without exacerbating the injury. It is often diffi- incidence of stress fractures. These include modifications cult to achieve compliance with total rest among Soldiers to physical training programs, use of shock-absorbing who are highly active; “relative rest” should be consid- insoles, vitamin D and calcium supplementation, modi- ered for these individuals. Relative rest involves reducing fications of equipment, and leadership education with the frequency (times per week), duration (minutes per injury surveillance. session), and/or intensity of the activity that is causing the discomfort. A reasonable recommendation may be Modification of Physical Training Programs to reduce the frequency or duration by half; a reduction It should not be surprising that many successful inter- in the intensity of the activity should also be considered. ventions to reduce the incidence of stress fractures in Frequency or duration can then be increased by 10% per the military have focused on modifications of group week with the caveat that continued pain may require physical training programs. These modifications have re-evaluation. Alternative exercises with less impact, involved reducing the frequency or duration of certain such as pool running, cycling, or other low-impact ex- physical activities or alternating exercised muscle groups ercises, should be considered and discussed with the Sol- in different exercise sessions so that previously exercised dier.13,111 One walk-to-run program is available at https:// muscle groups are provided rest and recovery (e.g., up- www.munson.amedd.army.mil/departments/PT/Walk per body versus lower body). The current Army physi- -RunProgression(Distance).pdf. In general, nonsteroidal cal training doctrine called Physical Readiness Training anti-inflammatory drugs should be avoided because of was specifically designed to reduce injuries through a adverse effects on osteoblastic cells.112 Other medications reduction in excessive running mileage, increase in ex- like acetaminophen might be considered to reduce pain. ercise variety (cross-training), and gradual progressive overload.43 It was shown to reduce stress fracture inci- High-risk fractures should be referred to an orthopedist. dence after implementation.123 Other studies have also Greater than 85% of stress fractures involve the lower shown that reducing excessive running and/or marching

124 Journal of Special Operations Medicine Volume 17, Edition 2/Summer 2017 All articles published in the Journal of Special Operations Medicine are protected by United States copyright law and may not be reproduced, distributed, transmitted, displayed, or otherwise published without the prior written permission of Breakaway Media, LLC. Contact [email protected]. mileage during training reduced stress fractures while Table 2 Meta-Analysis Showing Pooled Results of Studies resulting in similar improvements in aerobic fitness Examining the Effects of Insoles on Stress Fractures50,128–132 when compared with longer running or marching mile- Insole/No Insole age.124–126 One study involved multiple modifications to Insole/No Combined Meta- the physical activities during female Australian recruit Insole,133 OR Analysis,132,133 OR training. Reducing marching speed, allowing trainees to (95% CI) (95% CI) march at their own step length (rather than marching in Any stress 0.44 (0.25–0.78) 0.55 (0.43–0.69) step), running and marching in more widely spaced for- fracture mations, running on grass, and reducing running mile- Femoral stress 0.42 (0.24–0.75) 0.48 (0.30–0.78) age was successful in reducing pelvic stress fractures in fractures women.127 Tibial stress 0.51 (0.32–0.82) 0.46 (0.31–0.70) fractures Shock-Absorbing Insoles Metatarsal stress 0.29 (0.08–1.05) 0.74 (0.51–1.08) At least six studies have investigated whether shock-ab- fractures 50,128–132 sorbing insoles can prevent stress fractures. How- CI, confidence interval; OR, odds ratio. ever, evaluation of these investigations is complicated by differences in types of materials used (e.g., urethane, D were associated with a higher risk of stress fractures neoprene, viscoelastic polymer), shape of the insole (i.e., in military SMs.68,69,136,137 custom molded versus generic off-the-shelf), the length of the material (i.e., heel cup versus full length), and A meta-analysis of eight placebo-controlled studies in- method of stress fracture diagnosis (e.g., radiograph, volving elderly women suggested that supplementation bone scan). Despite these factors, when the results of five with vitamin D (with or without calcium) reduced the studies50,128–131 were pooled in a meta-analysis, there was incidence of nonvertebral fractures and hip fractures.138 an overall reduction in stress fracture incidence.133 The One study139 administered a dietary assessment at the protective effect was greater for femoral and tibial stress start of a study and followed female runners for stress fractures and less so for metatarsal stress fractures. The fractures for about 2 years. Investigators found that results of the meta-analysis (pooled results)133 are shown each additional cup of skim milk consumed at baseline in the second column of Table 2. Note that in Table 2, was associated with a 62% reduction in stress fracture an odds ratio <1 indicates the “protective” effect and incidence. There was a dose-response relationship such that insole group had a lower stress fracture risk. that higher baseline calcium consumption was associ- ated with a lower rate of subsequent stress fractures Since this meta-analysis133 was completed, one additional (secondary data analysis140). There was also a nonsig- study was published that examined the effectiveness of a nificant tendency for higher vitamin D intake to reduce cellular polyurethane foam insoles for the prevention of stress fracture incidence. stress fractures during British Royal Marine training.132 We added that study to the meta-analysis conducted pre- The only double-blind, placebo-controlled study55 ex- viously,133 using the random model in Comprehensive amining the influence of vitamin D and calcium con- Meta-Analysis Statistical Package (version 3). Results sumption on stress fractures was conducted among are shown in the third column of Table 2. Because of US female Navy recruits. One group was daily supple- the many individuals tested in the new study,132 the con- mented with 800IU of vitamin D and 2,000mg of cal- fidence interval around the estimated effects sizes were cium, while a second group received a placebo. At the considerably narrowed. Adding this study to the previ- end of the 8 weeks of training, the supplemented group ous five provided more support for the contention that had a 20% lower stress fracture incidence compared shock-absorbing insoles appear to reduce the incidence with the placebo group. Another study141 was conducted of stress fractures, especially in the femur and tibia. among male South African recruits who either did (n = 247) or did not (n = 1,151) receive a 500mg/d cal- Vitamin D and Calcium Supplementation cium supplement. Over 9 weeks of training, the supple- Vitamin D is important for bone health because it in- mented recruits had a 0.4% incidence of stress fracture, creases calcium absorption from the gastrointestinal whereas the nonsupplemented recruits had a 1.2% in- track and controls calcium deposition in the bone.134 cidence. However, because of the relatively small num- The current recommended daily allowance of vitamin D ber of stress fractures (n = 15), the difference was not is 600IU (15μg/d).135 25-hydroxyvitamin D [25(OH)D] statistically significant (p = .26, secondary data analy- is the accepted clinical indicator of vitamin D status and sis). Overall, there does appear to be some evidence that includes contributions from both cutaneous (solar) and higher levels of calcium and/or vitamin D intake may dietary sources. Several studies indicated that low levels reduce stress fracture incidence in military training, but of circulating 25(OH)D or low dietary intake of vitamin further research is certainly needed, especially in men.

Stress Fractures 125 All articles published in the Journal of Special Operations Medicine are protected by United States copyright law and may not be reproduced, distributed, transmitted, displayed, or otherwise published without the prior written permission of Breakaway Media, LLC. Contact [email protected].

Modification of Military Equipment Disclaimer At least one investigation142 has suggested that when The views expressed in this presentation are those of the men and women carry identical loads over identical dis- authors and do not necessarily reflect the official policy tances, women report considerable problems with load- of the Department of Defense, Department of the Army, carrying equipment. Especially prevalent were problems US Army Medical Department or the US Government. with straps of the rucksack, fit of pistol belts, The use of trademark names does not imply endorse- and fit and stability of the rucksack.142 One study modi- ment by the US Army but is intended only to assist in the fied the equipment of female Israeli border soldiers by identification of a specific product. using a shorter rifle; lighter, better-fitting combat vest; and reducing the total load carried by 25%. After the in- Disclosure terventions were introduced, there was a 56% reduction in stress fracture incidence.143 Another study modified The authors have nothing to disclose. the combat vest by approximating it to the female cen- ter of gravity and providing a more comfortable upper References body fit. However, this did not significantly affect stress 1. Nye NS, Covey CJ, Sheldon L, et al. Improving the diagnos- 144 fracture incidence in these soldiers. tic accuracy and efficiency of suspected bone stress injuries: algorithm and clinical prediction rule. Sports Health. 2016; Leadership Education, Enforcement, May–June:278–283. and Surveillance 2. Mattila VM, Niva M, Kiuru M, et al. Risk factors for bone stress injuries: a follow-up study of 102,515 person-years. Leadership education, enforcement of injury prevention Med Sci Sports Exerc. 2007;39:1061–1066. guidelines, and systematic surveillance were found to 3. Pepper M, Akuthota V, McCarty EC. 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126 Journal of Special Operations Medicine Volume 17, Edition 2/Summer 2017 All articles published in the Journal of Special Operations Medicine are protected by United States copyright law and may not be reproduced, distributed, transmitted, displayed, or otherwise published without the prior written permission of Breakaway Media, LLC. Contact [email protected].

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Sports Med. 1994;18:202–214. at the US Army Research Laboratory and epidemiology at

Stress Fractures 129 All articles published in the Journal of Special Operations Medicine are protected by United States copyright law and may not be reproduced, distributed, transmitted, displayed, or otherwise published without the prior written permission of Breakaway Media, LLC. Contact [email protected]. the US Army Public Health Center before retiring from civil a fellow of the American College of Physicians. She currently service in 2011. He is a fellow of the American College of serves as a medical and research consultant at the University of Sports Medicine, holds the Order of Military Medical Merit, West Florida (Pensacola, Florida) for the Military Sports and and is an adjunct professor at Uniformed Services University Operational Training Injuries Research Program in the Exer- (Bethesda, Maryland) and Bond University (Robina, Austra- cise Physiology Department. E-mail: [email protected]. lia). He currently works as a Knowledge Preservation Fellow at the Oak Ridge Institute for Science and Education. E-mail: CPT Hoedebecke serves as a family physician in the US [email protected]. Army and is board certified in family medicine. Additionally, he serves in the WONCA Polaris—the New and Future Family COL (Ret) Reynolds served as a physician in the US Army Physicians Movement of North America, covering 30 coun- for 25 years. During that time, she was board certified in in- tries and territories. He is a fellow of the American Academy ternal medicine and sports medicine. In addition to serving of Family Physicians, an assistant professor of family medicine as an internal medicine and sports medicine clinician at mili- at the Uniformed Services University (Bethesda, Maryland), tary hospitals, she conducted injury epidemiology studies with and sits on the editorial board of the J Family Med and Pri- combat forces while serving at the US Army Research Institute mary Care. With interests in global health, operational medi- of Environmental Medicine (Natick, Massachusetts). After cine, and medical education, Dr Hoedebecke has more than 40 retirement in 2002, she served as a team physician for cadet publications in eight languages across five continents. He cur- athletes at the US Coast Guard Academy (New London, Con- rently serves as the OIC of Yongsan Soldier Centered Medical necticut). She served as primary care sports medicine physician Home, K-16 clinic, and 1RC clinic (Yongsan, Korea). E-mail: at the Naval Hospital and Naval Air Technical Training Center [email protected]. Branch Clinic (Pensacola, Florida) from 2014 to 2016. She is

130 Journal of Special Operations Medicine Volume 17, Edition 2/Summer 2017