Risk factors for clinical stress fractures in male military recruits: a prospective cohort study

A multifactorial modeling to predicting tibial stress fractures: The role of tibial anatomy in adolescents

OBJECTIVE

This study aimed to investigate the impact of tibial anatomical structure, age, sex, average weekly exercise time during adolescence (AWETA), and BMI on the risk of tibial stress fractures (SF) and to develop a predictive model using logistic regression.

METHODS

We retrospectively analyzed 748 patients presenting with calf pain at our hospital from January 1, 2018, to August 31, 2023. After applying inclusion and exclusion criteria, 493 patients were categorized into the SF group (295 cases) and the control group (198 cases). Detailed patient information was collected, including height, weight, age, AWETA, history of recent prolonged exercise, and tibial measurements. Data were analyzed using appropriate statistical tests to determine between-group differences, and binary logistic regression analysis was performed to identify independent risk factors and develop a predictive model.

RESULTS

Body weight, BMI, AWETA, anteroposterior tibial plateau diameter, anterior tibial bowing angle, and gender showed significant differences between the SF and control groups. Logistic regression identified BMI (OR = 7.39, 95 % CI: 1.89-28.86), AWETA (OR = 0.54, 95 % CI: 0.46-0.62), and anterior tibial bowing angle (OR = 0.44, 95 % CI: 0.33-0.58) as independent predictors of tibial SF. The model demonstrated high predictive performance, with an AUC of 0.916, sensitivity of 93.9 %, and specificity of 89.4 %.

CONCLUSION

Anterior tibial bowing angle, BMI, and AWETA are strong predictors of tibial SF in young individuals. The developed predictive model provides a reliable tool for assessing tibial SF risk in clinical practice.

The Influence of Nutrition Intervention on the P1NP and CTX-1 Response to an Acute Exercise Bout: A Systematic Review with Meta-Analysis

BACKGROUND

Although nutrition and exercise both influence bone metabolism, little is currently known about their interaction, or whether nutritional intervention can modulate the bone biomarker response to acute exercise. Improved understanding of the relationships between nutrition, exercise and bone metabolism may have substantial potential to inform nutritional interventions to protect the bone health of exercising individuals, and to elucidate mechanisms by which exercise and nutrition influence bone.

OBJECTIVE

The aim was to synthesise available evidence related to the influence of nutrition on the response of the bone biomarkers procollagen type 1 N-terminal propeptide (P1NP) and C-terminal telopeptide of type 1 collagen (CTX-1) to acute exercise, using a systematic review and meta-analytic approach.

METHODS

Studies evaluating the influence of nutritional status or intervention on the bone biomarker response to an acute exercise bout were included and separated into four categories: (1) feeding status and energy availability, (2) macronutrients, (3) micronutrients and (4) other. Studies conducted on healthy human populations of any age or training status were included. Meta-analysis was conducted when data from at least five studies with independent datasets were available. In the case of insufficient data to warrant meta-analysis, results from individual studies were narratively synthesised and standardised mean effect sizes visually represented.

RESULTS

Twenty-two articles were included. Of these, three investigated feeding status or energy availability, eight macronutrients, eight micronutrients (all calcium) and six other interventions including dairy products or collagen supplementation. Three studies had more than one intervention and were included in all relevant outcomes. The largest and most commonly reported effects were for the bone resorption marker CTX-1. Meta-analysis indicated that calcium intake, whether provided via supplements, diet or infusion, reduced exercise-induced increases in CTX-1 (effect size - 1.1; 95% credible interval [CrI] -  2.2 to - 0.05), with substantially larger effects observed in studies that delivered calcium via direct infusion versus in supplements or foods. Narrative synthesis suggests that carbohydrate supplementation may support bone during acute exercise, via reducing exercise-induced increases in CTX-1. Conversely, a low-carbohydrate/high-fat diet appears to induce the opposite effect, as evidenced by an increased exercise associated CTX-1 response, and reduced P1NP response. Low energy availability may amplify the CTX-1 response to exercise, but it is unclear whether this is directly attributable to energy availability or to the lack of specific nutrients, such as carbohydrate.

CONCLUSION

Nutritional intervention can modulate the acute bone biomarker response to exercise, which primarily manifests as an increase in bone resorption. Ensuring adequate attention to nutritional factors may be important to protect bone health of exercising individuals, with energy, carbohydrate and calcium availability particularly important to consider. Although a wide breadth of data were available for this evidence synthesis, there was substantial heterogeneity in relation to design and intervention characteristics. Direct and indirect replication is required to confirm key findings and to generate better estimates of true effect sizes.

Immunology of Physical Exercise: Is Equus caballus an Appropriate Animal Model for Human Athletes?

Domestic horses routinely participate in vigorous and various athletic activities. This enables the horse to serve as a model for studying athletic physiology and immunology in other species, including humans. For instance, as a model of physical efforts, such as endurance rides (long-distance running/aerobic exercise) and races (anaerobic exercise), the horse can be useful in evaluating post-exercise response. Currently, there has been significant interest in finding biomarkers, which characterize the advancement of training and adaptation to physical exercise in the horse. The parallels in cellular responses to physical exercises, such as changes in receptor expression and blood cell activity, improve our understanding of the mechanisms involved in the body's response to intense physical activity. This study focuses on the changes in levels of the pro- and anti-inflammatory cytokines and cellular response in the context of post-exercise immune response. Both the direction of changes in cytokine levels and cellular responses of the body, such as proliferation and expression of surface markers on lymphocytes, monocytes and neutrophils, show cross-functional similarities. This review reveals that horses are robust research models for studying the immune response to physical exercise in human athletes.

Republication of "Stress Fractures of the Foot and Ankle in Athletes"

Stress fractures of the foot and ankle are common injuries in athletes. Management differs considerably based on fracture location and predisposing factors. Repetitive loading of the foot and ankle in athletes should result in physiologic bone remodeling in accordance with Wolff's law. However, when there is not sufficient time for complete healing to occur before additional loads are incurred, this process can instead lead to stress fracture. Assessment of the athlete's training regimen and overall bone health is paramount to both the discovery and treatment of these injuries, although diagnosis is often delayed in the setting of normal-appearing initial radiographs. While most stress fractures of the foot or ankle can usually be treated nonoperatively with a period of activity modification, fractures in certain locations are considered "high risk" due to poor intrinsic healing and may warrant more proactive operative management.

Current risks factors and emerging biomarkers for bone stress injuries in military personnel

INTRODUCTION

Bone stress injuries (BSIs) have plagued the military for over 150 years; they afflict around 5 to 10% of military recruits, more so in women, and continue to place a medical and financial burden on defence. While the tibia generally adapts to the rigours of basic military training, the putative mechanisms for bone maladaptation are still unclear.

METHODS

This paper provides a review of the published literature on current risk factors and emerging biomarkers for BSIs in military personnel; the potential for biochemical markers of bone metabolism to monitor the response to military training; and, the association of novel biochemical 'exerkines' with bone health.

RESULTS

The primary risk factor for BSI in military (and athletic) populations is too much training, too soon. Appropriate physical preparation before training will likely be most protective, but routine biomarkers will not yet identify those at risk. Nutritional interventions will support a bone anabolic response to training, but exposure to stress, sleep loss, and medication is likely harmful to bone. Monitoring physiology using wearables-ovulation, sleep and stress-offer potential to inform prevention strategies.

CONCLUSIONS

The risk factors for BSIs are well described, but their aetiology is very complex particularly in the multi-stressor military environment. Our understanding of the skeletal responses to military training is improving as technology advances, and potential biomarkers are constantly emerging, but sophisticated and integrated approaches to prevention of BSI are warranted.

Stress fractures

Stress fractures (SF) represent 10%-20% of all injuries in sport medicine. An SF occurs when abnormal and repetitive loading is applied on normal bone: The body cannot adapt quickly enough, leading to microdamage and fracture. The etiology is multifactorial with numerous risk factors involved. Diagnosis of SF can be achieved by identifying intrinsic and extrinsic factors, obtaining a good history, performing a physical exam, and ordering laboratory and imaging studies (magnetic resonance imaging is the current gold standard). Relative energy deficiency in sport (RED-S) is a known risk factor. In addition, for women, it is very important know the menstrual status to identify long periods of amenorrhea in the past and the present. Early detection is important to improve the chance of symptom resolution with conservative treatment. Common presentation involves complaints of localized pain, with or without swelling, and tenderness on palpation of bony structures that begins earlier in training and progressively worsens with activity over a 2- to 3-week period. Appropriate classification of SF based on type, location, grading, and low or high risk is critical in guiding treatment strategies and influencing the time to return to sport. Stress injuries at low-risk sites are typically managed conservatively. Studies have suggested that calcium and vitamin D supplementation might be helpful. Moreover, other treatment regimens are not well established. Understanding better the pathophysiology of SFs and the potential utility of current and future bone-active therapeutics may well yield approaches that could treat SFs more effectively.

Proportion of Navy Recruits Diagnosed With Symptomatic Stress Fractures During Training and Monetary Impact of These Injuries

BACKGROUND

Lower extremity stress fractures result in lost time from work and sport and incur costs in the military when they occur in service members. Hypovitaminosis D has been identified as key risk factor in these injuries. An estimated 33% to 90% of collegiate and professional athletes have deficient vitamin D levels. Other branches of the United States military have evaluated the risk factors for stress fractures during basic training, including vitamin D deficiency. To the best of our knowledge, a study evaluating the correlation between these injuries and vitamin D deficiency in US Navy recruits and a cost analysis of these injuries has not been performed. Cutbacks in military medical staffing mean more active-duty personnel are being deferred for care to civilian providers. Consequently, data that previously were only pertinent to military medical providers have now expanded to the nonmilitary medical community.

QUESTIONS/PURPOSES

We therefore asked: (1) What proportion of US Navy recruits experience symptomatic lower extremity stress fractures, and what proportion of those recruits had hypovitaminosis vitamin D on laboratory testing? (2) What are the rehabilitation costs involved in the treatment of lower extremity stress fractures, including the associated costs of lost training time? (3) Is there a cost difference in the treatment of stress fractures between recruits with lower extremity stress fractures who have vitamin D deficiency and those without vitamin D deficiency?

METHODS

We retrospectively evaluated the electronic medical record at Naval Recruit Training Command in Great Lakes, IL, USA, of all active-duty males and females trained from 2009 until 2015. We used ICD-9 and ICD-10 diagnosis codes to identify those diagnosed with symptomatic lower extremity stress fractures. Data collected included geographic region of birth, preexisting vitamin D deficiency, vitamin D level at the time of diagnosis, medical history, BMI, age, sex, self-reported race or ethnicity, hospitalization days, days lost from training, and the number of physical therapy, primary care, and specialty visits. To ascertain the proportion of recruits who developed symptomatic stress fractures, we divided the number of recruits who were diagnosed with a stress fracture by the total number who trained over that span of time, which was 204,774 individuals. During the span of this study, 45% (494 of 1098) of recruits diagnosed with a symptomatic stress fracture were female and 55% (604 of 1098) were male, with a mean ± SD age of 24 ± 4 years. We defined hypovitaminosis D as a vitamin D level lower than 40 ng/mL. Levels less than 40 ng/mL were defined as low normal and levels less than 30 ng/mL as deficient. Vitamin D levels were obtained at the discretion of the individual treating provider without standardization of protocol. Cost was defined as physical therapy visits, primary care visits, orthopaedic visits, diagnostic imaging costs, laboratory costs, hospitalizations, if applicable, and days lost from training. Diagnostic studies and laboratory tests were incorporated as indirect costs into initial and follow-up physical therapy visits. Evaluation and management code fee schedules for initial visits and follow-up visits were used as direct costs. We obtained these data from the Centers for Medicare & Medicaid Services website. Per capita cost was calculated by taking the total cost and dividing it by the study population. Days lost from training is based on a standardized government military salary of recruits to include room and board.

RESULTS

We found that 0.5% (1098 of 204,774) of recruits developed a symptomatic lower extremity stress fracture. Of the recruits who had vitamin D levels drawn at the time of stress fracture, 95% (416 of 437 [95% confidence interval (CI) 94% to 98%]; p > 0.99) had hypovitaminosis D (≤ 40 ng/mL) and 82% (360 of 437 [95% CI 79% to 86%]; p > 0.99) had deficient levels (≤ 30 ng/mL) on laboratory testing, when evaluated. The total treatment cost was USD 9506 per recruit. Days lost in training was a median of 56 days (4 to 108) for a per capita cost of USD 5447 per recruit. Recruits with deficient vitamin D levels (levels ≤ 30 ng/mL) incurred more physical therapy treatment costs than did those with low-normal vitamin D levels (levels 31 to 40 ng/mL) (mean difference USD 965 [95% CI 2 to 1928]; p = 0.049).

CONCLUSION

The cost of lost training and rehabilitation associated with symptomatic lower extremity stress fractures represents a major financial burden. Screening for and treatment of vitamin D deficiencies before recruit training could offer a cost-effective solution to decreasing the stress fracture risk. Recognition and treatment of these deficiencies has a role beyond the military, as hypovitaminosis and stress fractures are common in collegiate or professional athletes.

LEVEL OF EVIDENCE

Level III, prognostic study.

Activity specific areal bone mineral density is reduced in athletes with stress fracture and requires profound recovery time: A study of lumbar stress fracture in elite cricket fast bowlers

OBJECTIVES

The aims of this study were to determine whether lumbar areal bone mineral density differed between cricket fast bowlers with and without lumbar stress fracture, and whether bone mineral density trajectories differed between groups during rehabilitation.

DESIGN

Cross-sectional and cohort.

METHODS

29 elite male fast bowlers received a post-season anteroposterior lumbar dual-energy X-ray absorptiometry scan and a lumbar magnetic resonance imaging scan to determine stress fracture status. Participants were invited for three additional scans across the 59 weeks post baseline or diagnosis of injury. Bone mineral density was measured at L1 - L4 and ipsilateral and contralateral L3 and L4 sites. Independent-sample t-tests determined baseline differences in bone mineral density and multilevel models were used to examine differences in bone mineral density trajectories over time between injured and uninjured participants.

RESULTS

17 participants with lumbar stress fracture had lower baseline bone mineral density at L1 - L4 (7.6 %, p = 0.034) and contralateral sites (8.8-10.4 %, p = 0.038-0.058) than uninjured participants. Bone mineral density at all sites decreased 1.9-3.0 % by 20-24 weeks before increasing to above baseline levels by 52 weeks post injury.

CONCLUSIONS

Injured fast bowlers had lower lumbar bone mineral density at diagnosis that decreased following injury and did not return to baseline until up to a year post-diagnosis. Localised maladaptation of bone mineral density may contribute to lumbar stress fracture. Bone mineral density loss following injury may increase risk of recurrence, therefore fast bowlers require careful management when returning to play.

Sex differences in tibial adaptations to arduous training: An observational cohort study

Military training increases tibial density and size, but it is unknown if men and women adapt similarly to the same arduous training. Seventy-seven men and 57 women not using hormonal contraceptives completed this study. Tibial volumetric bone mineral density (vBMD) and geometry were measured by peripheral quantitative computed tomography (4%, 14%, 38%, and 66% sites) at the start (week 1) and end (week 14) of British Army basic training. Training increased trabecular vBMD (4% site in men; 4% and 14% sites in women), cortical vBMD (38% site), total area (14% and 38% sites), trabecular area (14% site), cortical area and thickness (14%, 38%, and 66% sites), periosteal perimeter (14%, 38%, and 66% sites), and all indices of estimated strength (14%, 38%, and 66% sites); and, decreased endosteal perimeter (66% site) in men and women (all p ≤ 0.045). The increase in trabecular vBMD (4% and 14% sites) was greater in women and the increases in cortical area and strength (38% site) were greater in men (sex × time interactions, all p ≤ 0.047). P1NP increased and βCTX and sclerostin decreased during training in men and women, consistent with adaptive bone formation. PTH decreased in men but increased in women. Arduous weight-bearing activity increased the density and size of the tibia after 14 weeks. Women experienced similar tibial adaptations as men, however, a greater increase in trabecular vBMD in women compared with men could be due to higher loading at this skeletal site in women, whereas the small increase in cortical area could be due to inhibitory effects of oestradiol.

Mechanical Differences between Men and Women during Overground Load Carriage at Self-Selected Walking Speeds

Few studies have directly compared physical responses to relative loading strategies between men and women during overground walking. This study aimed to compare gait mechanics of men and women during overground load carriage. A total of 30 participants (15 male, 15 female) completed three 10-min walking trials while carrying external loads of 0%, 20% and 40% of body mass at a self-selected walking speed. Lower-body motion and ground reaction forces were collected using a three-dimensional motion capture system and force plates, respectively. Female participants walked with a higher cadence (p = 0.002) and spent less absolute time in stance (p = 0.010) but had similar self-selected walking speed (p = 0.750), which was likely due to the female participants being shorter than the male participants. Except for ankle plantarflexion moments, there were no sex differences in spatiotemporal, kinematic, or kinetic variables (p > 0.05). Increasing loads resulted in significantly lower self-selected walking speed, greater stance time, and changes in all joint kinematics and kinetics across the gait cycle (p < 0.05). In conclusion, there were few differences between sexes in walking mechanics during overground load carriage. The changes identified in this study may inform training programs to increase load carriage performance.

The Relationship Between Stress Fractures and Bone Turnover Markers Is Unclear in Athletic and Military Populations: A Critically Appraised Topic

Clinical Scenario: Having an indication of how bone is remodeling in response to training load could help identify athletes and military personnel at increased stress fracture (SFx) risk. Direct assessment of bone remodeling is impractical. Biochemical markers of bone turnover are used as an indirect measure of bone remodeling and have potential to inform prevention and treatment efforts. To date, the relationship between bone turnover markers and SFxs in athletes or military personnel remains unclear. Clinical Question: Are SFxs related to bone turnover markers in athletes and military personnel? Summary of Key Findings: Seven met eligibility criteria. In five studies, an association between SFxs and bone turnover markers existed. Clinical Bottom Line: The evidence supporting a relationship between SFxs and bone turnover markers in athletes and military personnel is mixed. While five of the seven studies reported some type of relationship, no studies prospectively measured bone turnover markers in a group of athletes or military personnel without an SFx or without SFx history and followed them over time to reassess bone turnover markers upon SFx occurrence. Strength of Clinical Recommendation: In accordance with the Strength of Recommendation Taxonomy, Grade C is the most appropriate strength of recommendation rating.

Risk factors for musculoskeletal injuries in the military: a qualitative systematic review of the literature from the past two decades and a new prioritizing injury model

BACKGROUND

Musculoskeletal injuries (MSkIs) are a leading cause of health care utilization, as well as limited duty and disability in the US military and other armed forces. MSkIs affect members of the military during initial training, operational training, and deployment and have a direct negative impact on overall troop readiness. Currently, a systematic overview of all risk factors for MSkIs in the military is not available.

METHODS

A systematic literature search was carried out using the PubMed, Ovid/Medline, and Web of Science databases from January 1, 2000 to September 10, 2019. Additionally, a reference list scan was performed (using the "snowball method"). Thereafter, an international, multidisciplinary expert panel scored the level of evidence per risk factor, and a classification of modifiable/non-modifiable was made.

RESULTS

In total, 176 original papers and 3 meta-analyses were included in the review. A list of 57 reported potential risk factors was formed. For 21 risk factors, the level of evidence was considered moderate or strong. Based on this literature review and an in-depth analysis, the expert panel developed a model to display the most relevant risk factors identified, introducing the idea of the "order of importance" and including concepts that are modifiable/non-modifiable, as well as extrinsic/intrinsic risk factors.

CONCLUSIONS

This is the qualitative systematic review of studies on risk factors for MSkIs in the military that has attempted to be all-inclusive. A total of 57 different potential risk factors were identified, and a new, prioritizing injury model was developed. This model may help us to understand risk factors that can be addressed, and in which order they should be prioritized when planning intervention strategies within military groups.

Does vitamin D supplementation prevent SARS-CoV-2 infection in military personnel? Review of the evidence

For most individuals residing in Northwestern Europe, maintaining replete vitamin D status throughout the year is unlikely without vitamin D supplementation and deficiency remains common. Military studies have investigated the association with vitamin D status, and subsequent supplementation, with the risk of stress fractures particularly during recruit training. The expression of nuclear vitamin D receptors and vitamin D metabolic enzymes in immune cells additionally provides a rationale for the potential role of vitamin D in maintaining immune homeostasis. One particular area of interest has been in the prevention of acute respiratory tract infections (ARTIs). The aims of this review were to consider the evidence of vitamin D supplementation in military populations in the prevention of ARTIs, including SARS-CoV-2 infection and consequent COVID-19 illness. The occupational/organisational importance of reducing transmission of SARS-CoV-2, especially where infected young adults may be asymptomatic, presymptomatic or paucisymptomatic, is also discussed.

Bone, Biomarker, Body Composition, and Performance Responses to 8 Weeks of ROTC Training

CONTEXT

Military personnel engage in vigorous exercise, often resulting in higher bone mineral density; however, lower leg bone injuries are common in this population. Predictors of change in tibial bone quality and strength need to be characterized in this high-risk population.

OBJECTIVE

This study aimed to examine the effects of an eight-week military training intervention on total body and site-specific bone density and tibial bone quality, serum biomarkers (parathyroid hormone and sclerostin), body composition, and physical performance. Additionally, we sought to investigate what outcome variables (biomarkers, body composition, physical performance) would be predictive of estimated tibial bone strength in college-aged Reserve Officers' Training Corps (ROTC) members.

DESIGN

Prospective Cohort Study.

SETTING

XXX University. Patients of Other Participants: ROTC (n=14 male; n=4 female) were matched for sex, age, and body mass to physically active Controls (n=14 male; n=4 female). ROTC engaged in an eight-week training intervention, while physically active Controls made no changes to their exercise routines.

MAIN OUTCOME MEASURES

Pre general health questionnaires and pre, mid, and post intervention bone scans (DXA, pQCT), serum blood draws (parathyroid hormone and sclerostin), and physical performance measures (muscle strength and aerobic capacity) were tested.

RESULTS

ROTC participants exhibited significantly increased hip bone density and content (all p≤0.03) after the eight-week intervention. Sclerostin, not PTH, was a significant positive correlate and predictor in all ROTC models for estimated bone strength at the fracture prone 38% tibial site. Both groups decreased total body and regional fat mass and ROTC increased aerobic capacity (all p≤0.05).

CONCLUSIONS

All bone, body composition, and performance measures either improved or were maintained in response to ROTC training and sclerostin should be further investigated as a potential early indicator of changes in estimated tibial bone strength in military cohorts.

Risk Factors, Diagnosis and Management of Bone Stress Injuries in Adolescent Athletes: A Narrative Review

Physical activity is known to be beneficial for bone; however, some athletes who train intensely are at risk of bone stress injury (BSI). Incidence in adolescent athlete populations is between 3.9 and 19% with recurrence rates as high as 21%. Participation in physical training can be highly skeletally demanding, particularly during periods of rapid growth in adolescence, and when competition and training demands are heaviest. Sports involving running and jumping are associated with a higher incidence of BSI and some athletes appear to be more susceptible than others. Maintaining a very lean physique in aesthetic sports (gymnastics, figure skating and ballet) or a prolonged negative energy balance in extreme endurance events (long distance running and triathlon) may compound the risk of BSI with repetitive mechanical loading of bone, due to the additional negative effects of hormonal disturbances. The following review presents a summary of the epidemiology of BSI in the adolescent athlete, risk factors for BSI (physical and behavioural characteristics, energy balance and hormone disruption, growth velocity, sport-specific risk, training load, etc.), prevention and management strategies.

Effects of body size and load carriage on lower-extremity biomechanical responses in healthy women

BACKGROUND

Musculoskeletal injuries, such as stress fractures, are the single most important medical impediment to military readiness in the U.S. Army. While multiple studies have established race- and sex-based risks associated with a stress fracture, the role of certain physical characteristics, such as body size, on stress-fracture risk is less conclusive.

METHODS

In this study, we investigated the effects of body size and load carriage on lower-extremity joint mechanics, tibial strain, and tibial stress-fracture risk in women. Using individualized musculoskeletal-finite-element-models of 21 women of short, medium, and tall statures (n = 7 in each group), we computed the joint mechanics and tibial strains while running on a treadmill at 3.0 m/s without and with a load of 11.3 or 22.7 kg. We also estimated the stress-fracture risk using a probabilistic model of bone damage, repair, and adaptation.

RESULTS

Under all load conditions, the peak plantarflexion moment for tall women was higher than those in short women (p < 0.05). However, regardless of the load condition, we did not observe differences in the strains and the stress-fracture risk between the stature groups. When compared to the no-load condition, a 22.7-kg load increased the peak hip extension and flexion moments for all stature groups (p < 0.05). However, when compared to the no-load condition, the 22.7-kg load increased the strains and the stress-fracture risk in short and medium women (p < 0.05), but not in tall women.

CONCLUSION

These results show that women of different statures adjust their gait mechanisms differently when running with external load. This study can educate the development of new strategies to help reduce the risk of musculoskeletal injuries in women while running with external load.

Changes in Volumetric Bone Mineral Density Over 12 Months After a Tibial Bone Stress Injury Diagnosis: Implications for Return to Sports and Military Duty

BACKGROUND

Bone stress injuries (BSIs) occur in up to 20% of runners and military personnel. Typically, after a period of unloading and gradual return to weightbearing activities, athletes return to unrestricted sports participation or military duty approximately 4 to 14 weeks after a BSI diagnosis, depending on the injury location and severity. However, the time course of the recovery of the bone's mechanical competence is not well-characterized, and reinjury rates are high.

PURPOSE

To assess the bone microarchitecture and volumetric bone mineral density (vBMD) over 12 months after a tibial BSI diagnosis.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

We enrolled 30 female athletes from the local community (aged 18-35 years) with a tibial BSI (grade ≥2 of 4 on magnetic resonance imaging) for this prospective observational study. Participants completed a baseline visit within 3 weeks of the diagnosis. At baseline and 6, 12, 24, and 52 weeks after the BSI diagnosis, we collected high-resolution peripheral quantitative computed tomography scans of the ultradistal tibia (4% of tibial length) of the injured and uninjured legs as well as pain and physical activity assessment findings.

RESULTS

From baseline to 12 weeks after the diagnosis, total, trabecular, and cortical vBMD declined by 0.58% to 0.94% (P < .05 for all) in the injured leg. Total and trabecular vBMD also declined by 0.61% and 0.67%, respectively, in the uninjured leg (P < .05 for both). At 24 weeks, mean values for all bone parameters were nearly equivalent to baseline values, and by 52 weeks, several mean values had surpassed baseline values. Of the 30 participants, 10 incurred a subsequent BSI during the course of the study, and 1 of these 10 incurred 2 subsequent BSIs. Participants who suffered an additional BSI were younger and had a later age of menarche, a greater incidence of previous fractures, and lower serum parathyroid hormone levels (P < .05 for all).

CONCLUSION

Bone density declined in both the injured and the uninjured legs and, on average, did not return to baseline for 3 to 6 months after a tibial BSI diagnosis. The observed time to the recovery of baseline vBMD, coupled with the high rate of recurrent BSIs, suggests that improved return-to-sports and military duty guidelines may be in order.

Study on Overload Injuries during Periods of Intense Physical Activity Complemented by Isokinetic Dynamometry Evaluation

Objective  The present study aims to measure the incidence of overload injuries in training soldiers, who are subjected to intense physical exercise, and to compare it with a control group. Next, it intends to verify whether there is any relationship between overload injuries and some neuromuscular function parameters.

Methods  Analytical, prospective observational study. Both the observational and the control group consisted of soldiers from the Portuguese Army. Clinical evaluation was performed by medical interview in the week prior to the beginning of a military parachuting course and in the week immediately after its completion. The neuromuscular performance was assessed by isokinetic dynamometry during the medical interview.

Results  With 44 of the 57 military personnel in training complaining of pain, the observational group had significantly more injuries than the control group ( p < 0.001). Five complaints had traumatic origin and 39 were overload injuries. Of the 39 military personnel with overload injuries, 21 reported limited sports performance. However, isokinetic dynamometry showed no statistically significant differences in neuromuscular performance ( p  = 0.223 and p  = 0.229).

Conclusion  Military personnel in training are prone to overload injuries, with an incidence rate > 70%. The implementation of strategies for injury monitoring and prevention is critical to promote health and physical capacity.

Grade 4 Distal Femur Stress Fracture in a Long-Distance Hiker on the Appalachian Trail

Although stress injuries are a common occurrence in sports medicine clinics, a distal femur stress fracture is less so. Early detection can result in a favorable prognosis and may prevent the need for surgical intervention. A misdiagnosis resulting in delay of care can result in significant complications. This case report documents a rare distal femur stress fracture in a long-distance hiker. A 35-y-old male presented to an orthopedic clinic in Pennsylvania with left knee pain after completing 1423 km (884 mi) of the Appalachian trail over a 4-mo period. He was attempting a thru-hike, a specialized type of backpacking focused on completing a trail from end-to-end. Thru-hiking of this trail involves backpacking between Georgia and Maine, covering about 3540 km (2200 mi) with approximately 141,580 m (464,500 ft) of gain/loss in elevation. His pain began 2 mo into his hike when he noted medial sided left knee discomfort. Over the following 2 mo he sought treatment at 2 different locations along the trail with etiology undetermined. Upon evaluation in Pennsylvania, history and physical exam were suggestive of a stress fracture. Radiologic studies confirmed a closed nondisplaced nonangulated grade 4 transverse fracture of the shaft of the distal left femur. The patient was instructed to terminate his hike immediately and he was placed on nonweight bearing status. This case illustrates the importance of considering a distal femur stress fracture for the differential diagnosis of persistent knee pain in a long-distance hiker.

Prevalence of Vitamin D Insufficiency and Deficiency in Young, Female Patients With Lower Extremity Musculoskeletal Complaints

BACKGROUND

Low levels of vitamin D have well-known impacts on bone health, but vitamin D also has a more global role throughout many tissues, including skeletal muscle. The high prevalence of hypovitaminosis D and the vast physiological features of vitamin D have led researchers to examine the influence of vitamin D on physical performance and injury. Because of the critical role of vitamin D in maintaining musculoskeletal health and function, a high rate of hypovitaminosis D among female patients with a variety of musculoskeletal issues could be of high clinical relevance.

HYPOTHESIS

There is a high prevalence of low vitamin D in female patients with both acute and overuse sports-related issues of both soft tissue and bone.

STUDY DESIGN

Prospective cohort study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Female patients, aged 16 to 40 years, presenting with lower extremity injury diagnosed within the past 4 weeks, no use of multivitamin or vitamin D supplement, and no history of malabsorption syndrome met the inclusion criteria. Vitamin D levels were assessed and categorized as normal (≥32 ng/mL) and low, which includes insufficient (20.01-31.9 ng/mL) and deficient (≤20 ng/mL).

RESULTS

Of the 105 patients enrolled, 65.7% had low vitamin D. Within the low vitamin D cohort, 40.6% were deficient and 59.4% were insufficient. Injuries were grouped into overuse or acute with 74 overuse injuries and 31 acute injuries, exhibiting low vitamin D prevalence of 60.8% and 77.4%, respectively. Patients with ligamentous/cartilaginous injuries exhibited the highest percentage of low vitamin D (76.5%), followed by those with patellofemoral-related complaints (71.0%), muscle/tendon injuries (54.6%), and bone stress injuries (45.5%). In univariable analysis, older age, non-White race, less physical activity, less high-intensity interval training days, less endurance training days, and more rest days showed an association with low vitamin D, but none showed an independent association in multivariable analysis.

CONCLUSION

The prevalence of low vitamin D in female patients with various musculoskeletal complaints was high. Clinicians should evaluate for low vitamin D in both acute and overuse injuries.

CLINICAL RELEVANCE

In addition to screening, this study suggests that clinicians should evaluate for low vitamin D levels beyond bone stress injuries in the setting of acute and overuse injuries.

The Bone Metabolic Response to Exercise and Nutrition

Bone (re)modeling markers can help determine how the bone responds to different types, intensities, and durations of exercise. They also might help predict those at risk of bone injury. We synthesized evidence on the acute and chronic bone metabolic responses to exercise, along with how nutritional factors can moderate this response. Recommendations to optimize future research efforts are made.

Systematic Review and Meta-Analysis of Candidate Gene Association Studies With Fracture Risk in Physically Active Participants

Background: Fractures are common in physically active populations and genetic differences may mediate injury risk.

Objective: To meta-analyse the pooled results of candidate gene association studies with non-osteoporotic fracture risk in physically active humans.

Methods: Systematic searching of databases returned 11 eligible studies published in English. Pooled odds ratios (ORs) with 95% confidence intervals (CI) were produced using allele contrast, recessive and homozygote contrast meta-analysis models to evaluate associations of risk alleles in the COL1A1 (rs1800012), COL2A1 (rs412777), CTR (rs1801197), ESR1 (rs2234693 and rs9340799) LRP5 (rs3736228), VDR (rs10735810, rs7975232, rs1544410, and rs731236) genes with fracture incidence.

Results: Eligible study quality was generally low (7/11) and no significant overall effect was found for any genetic variant with any comparison model (p > 0.05). A trivial reduction in fracture risk was found for female participants with the COL1A1 Sp1 (rs1800012) T allele (OR = 0.48, 95% CI = 0.25–0.91, p = 0.03, d = –0.18).

Conclusions: No overall effect was found from the pooled results of included genetic variants on fracture risk in physically active participants. The COL1A1 Sp1 rs1800012 T allele may reduce fracture risk in physically active females but further high-quality research with sex-specific analysis is required.

Trial Registration: (PROSPERO; CRD42018115008).

Risk of Injury in Royal Air Force Training: Does Sex Really Matter?

INTRODUCTION

Musculoskeletal injuries are common during military and other occupational physical training programs. Employers have a duty of care to reduce employees' injury risk, where females tend to be at greater risk than males. However, quantification of principle co-factors influencing the sex-injury association, and their relative importance, remain poorly defined. Injury risk co-factors were investigated during Royal Air Force (RAF) recruit training to inform the strategic prioritization of mitigation strategies.

MATERIAL AND METHODS

A cohort of 1,193 (males n = 990 (83%); females n = 203 (17%)) recruits, undertaking Phase-1 military training, were prospectively monitored for injury occurrence. The primary independent variable was sex, and potential confounders (fitness, smoking, anthropometric measures, education attainment) were assessed pre-training. Generalized linear models were used to assess associations between sex and injury.

RESULTS

In total, 31% of recruits (28% males; 49% females) presented at least one injury during training. Females had a two-fold greater unadjusted risk of injury during training than males (RR = 1.77; 95% CI 1.49-2.10). After anthropometric, lifestyle and education measures were included in the model, the excess risk decreased by 34%, but the associations continued to be statistically significant. In contrast, when aerobic fitness was adjusted, an inverse association was identified; the injury risk was 40% lower in females compared with males (RR = 0.59; 95% CI: 0.42-0.83).

CONCLUSIONS

Physical fitness was the most important confounder with respect to differences in males' and females' injury risk, rather than sex alone. Mitigation to reduce this risk should, therefore, focus upon physical training, complemented by healthy lifestyle interventions.

Bone Stress Injuries Are Associated With Differences in Bone Microarchitecture in Male Professional Soldiers

Bone stress injuries are commonly due to repetitive loading, as often described in competitive athletes or military recruits. The underlying pathophysiology of bone stress injuries is multifactorial. The present cross-sectional study investigated (i) cortical and trabecular bone microstructure as well as volumetric bone mineral density in subjects with bone stress injuries at the tibial diaphysis, measured at the distal tibia and the distal radius by means of high-resolution peripheral quantitative computed tomography (CT), (ii) areal bone mineral density using dual-energy X-ray absorptiometry as well as calcaneal dual X-ray absorptiometry and laser, and (iii) the influence on bone turnover markers of formation and resorption at the early phase after injury. A total of 26 Caucasian male professional soldiers with post-training bone stress injury at the tibial diaphysis were included (case group). A total of 50 male, Caucasian professional soldiers from the same military institution served as controls (control group). High-resolution peripheral quantitative CT revealed a higher total area at the radius within the case group. Cortical bone mineral density was reduced at the radius and tibia within the case group. The trabecular number and trabecular thickness were reduced at the tibia in the case group. The trabecular network was more inhomogeneous at the radius and tibia within the case group. Calcaneal dual X-ray absorptiometry and laser was significantly reduced in the case group. This study quantified differences in bone microstructure among otherwise healthy individuals. Differences in bone microarchitecture may impair the biomechanical properties by increasing the susceptibility to sustain bone stress injuries. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2516-2523, 2019.

Lumbar bone mineral asymmetry in elite cricket fast bowlers

PURPOSE

Bone responds to mechanical loading by increasing bone mineral density (BMD) and/or bone area to enhance bone strength at the site of the greatest strain. Such localised adaptation has not been demonstrated at the spine. The aim of this study is to determine if BMD and/or bone mineral content (BMC) differs between dominant (ipsilateral to bowling/throwing arm) and non-dominant sides of the vertebrae in cricket fast bowlers, and whether this asymmetry differs according to stress fracture or disc injury history. A further aim was to determine if regional BMD and BMC in the lumbar spine differ between fast bowlers, other cricketers, rugby players and non-active controls, to highlight the site-specific response of lumbar vertebra to unilateral activity.

METHODS

23 fast bowlers, 14 other cricketers, 22 rugby players and 20 controls underwent an antero-posterior (AP) and lateral DXA scans of their lumbar spine to assess BMD, BMC and area. A custom analysis measured BMD and BMC of the dominant and non-dominant sides (lateral 33%) of the AP lumbar spine. BMD and BMC were compared between groups, injury status, vertebrae and sides using ANOVA.

RESULTS

Analysis of medical records showed that 6 fast bowlers had a history of lumbar stress fracture. Significantly greater BMD and BMC was found in the L4 non-dominant vertebra compared with the dominant vertebra in fast bowlers. BMD and BMC differed significantly according to vertebra, side and group, with fast bowlers having significantly greater BMD and BMC at the L3 and L4 non-dominant vertebra compared with other groups (L3: 13.3%-45.3%, L4: 15.7%-44.0%) compared with other groups. Fast bowlers who never suffered lumbar stress fracture had 3.6% and 1.7% greater BMD in the dominant and non-dominant sides of lumbar vertebrae respectively compared with those who did suffer lumbar stress fracture, but evidence of this was weaker (P = 0.08).

CONCLUSION

The lumbar spine responds to a unique unilateral high loading activity through site-specific increased bone mass at the site of most strain. Fast bowlers had increased lumbar BMD, particularly on the non-dominant side of L4, although this adaptation was less marked in those with history of lumbar stress fracture. Site-specific low bone mineral density within the lumbar side may be implicated in the aetiology of lumbar stress fracture.

Bone geometry and lower extremity bone stress injuries in male runners

Bone stress injuries (BSI) are common among distance runners and research investigations examining risk factors for BSI among men are limited. Therefore, investigations are needed to determine if men with a history of BSI have skeletal properties that may heighten BSI incidence.

OBJECTIVES

To analyze differences in bone density, bone geometry, and estimates of bone strength in male runners with and without a BSI history.

DESIGN

Cross-sectional.

METHODS

We recruited 36 male distance runners ages 18-41 for this study. We used peripheral quantitative computed tomography (pQCT) to assess volumetric bone mineral density (vBMD, mg/mm³), bone geometry (total and cortical bone area, mm²), tibia robustness (total area/tibia length, mm) and estimates of bone strength (section modulus and polar strength-strain index, mm³) at 5 tibial sites.

RESULTS

After adjusting for age, the BSI group had more slender tibias (9%), lower stress strain indices (-16%), lower section moduli (-17%) and smaller total cross-sectional (-11%) and cortical areas (-12%) at the 66% site of the tibia compared with controls (P < 0.05 for all). Similar differences were found at all other measurement sites. After adjusting for body size, differences in bone outcomes remained significant at the 66% site.

CONCLUSIONS

These results indicate that men with a history of BSI have lower estimated bending strength compared to controls because of narrower tibias. However, differences are largely attenuated in the distal ½ of the tibia after adjusting for body size. Thus, smaller tibia size, particularly at the mid-diaphysis, may be an important indicator for BSI incidence.

Effects of a contoured foot orthosis and flat insole on plantar pressure and tibial acceleration while walking in defence boots

This study investigated the effects of a contoured, prefabricated foot orthosis and a flat insole on plantar pressure and tibial acceleration while walking in defence boots. Twenty-eight adults walked along an 8-metre walkway in a: (i) defence boot (control condition), (ii) defence boot with a flat insole, and (iii) defence boot with a contoured foot orthosis. Plantar pressure data were collected using the pedar-X in-shoe system and tibial accelerations were measured with an accelerometer. In relation to plantar pressure under the rearfoot, the contoured foot orthosis, compared to the defence boot, decreased peak pressure and maximum force, and increased contact area. Under the medial midfoot, the contoured foot orthosis and flat insole increased peak pressure, maximum force and contact area. Under the medial forefoot, the contoured foot orthosis and flat insole increased maximum force. Under the lateral forefoot, the contoured foot orthosis and flat insole increased contact area, with the flat insole also increasing maximum force. In relation to tibial acceleration, the contoured foot orthosis, compared to the defence boot, decreased tibial peak positive acceleration. These findings provide novel biomechanical evidence for the effects of contoured foot orthoses in defence boots.

High prevalence of vitamin D insufficiency in professional handball athletes

OBJECTIVES

Vitamin D affects multiple body functions through the regulation of gene expression. In sports medicine, its influence on musculoskeletal health and performance is of particular interest. Vitamin D insufficiency might decrease athletic performance and increase the risk of musculoskeletal injuries. Several studies have demonstrated vitamin D deficiency in professional athletes; however, the prevalence of vitamin D insufficiency in professional handball players is yet unknown.

METHODS

The study was planned as a prospective, non-interventional study. We examined 70 male elite handball athletes (first league) in a pre-competition medical assessment in July. Age, height, weight, body mass index, 25-OH vitamin D, calcium, and parathyroid hormone were evaluated, and a sun exposure score was calculated. Players were then divided into two groups of vitamin D levels: insufficient (<30 ng/mL) and sufficient (≥30 ng/mL).

RESULTS

The mean 25-OH vitamin D level of the 70 players was 33.5 ± 10.9 ng/mL (median 32.2, IQR 26.5-38.9 ng/mL). Thirty-nine (55.7%) had sufficient and 31 (44.3%) insufficient levels. Athletes with sufficient vitamin D levels had significantly lower parathyroid hormone levels than athletes with insufficiency (24.9 ± 12.1 vs. 33.5 ± 15.1 ng/mL, p = 0.02). All other parameters evaluated demonstrated no significant difference between the two groups.

CONCLUSION

Vitamin D insufficiency is a common finding in professional handball athletes even in summer, which might negatively affect physical performance. Furthermore, it might lead to an increased risk of musculoskeletal injuries and infections. This should be evaluated in further studies.

Serum 25-hydroxyvitamin D fluctuations in military personnel during 6-month summer operational deployments in Afghanistan

Soldier operational performance is determined by their fitness, nutritional status, quality of rest/recovery, and remaining injury/illness free. Understanding large fluctuations in nutritional status during operations is critical to safeguarding health and well-being. There are limited data world-wide describing the effect of extreme climate change on nutrient profiles. This study investigated the effect of hot-dry deployments on vitamin D status (assessed from 25-hydroxyvitamin D (25(OH)D) concentration) of young, male, military volunteers. Two data sets are presented (pilot study, n 37; main study, n 98), examining serum 25(OH)D concentrations before and during 6-month summer operational deployments to Afghanistan (March to October/November). Body mass, percentage of body fat, dietary intake and serum 25(OH)D concentrations were measured. In addition, parathyroid hormone (PTH), adjusted Ca and albumin concentrations were measured in the main study to better understand 25(OH)D fluctuations. Body mass and fat mass (FM) losses were greater for early (pre- to mid-) deployment compared with late (mid- to post-) deployment (P<0·05). Dietary intake was well-maintained despite high rates of energy expenditure. A pronounced increase in 25(OH)D was observed between pre- (March) and mid-deployment (June) (pilot study: 51 (sd 20) v. 212 (sd 85) nmol/l, P<0·05; main study: 55 (sd 22) v. 167 (sd 71) nmol/l, P<0·05) and remained elevated post-deployment (October/November). In contrast, PTH was highest pre-deployment, decreasing thereafter (main study: 4·45 (sd 2·20) v. 3·79 (sd 1·50) pmol/l, P<0·05). The typical seasonal cycling of vitamin D appeared exaggerated in this active male population undertaking an arduous summer deployment. Further research is warranted, where such large seasonal vitamin D fluctuations may be detrimental to bone health in the longer-term.

Stress Fractures of the Foot and Ankle in Athletes

Stress fractures of the foot and ankle are common injuries in athletes. Management differs considerably based on fracture location and predisposing factors. Repetitive loading of the foot and ankle in athletes should result in physiologic bone remodeling in accordance with Wolff’s law. However, when there is not sufficient time for complete healing to occur before additional loads are incurred, this process can instead lead to stress fracture. Assessment of the athlete’s training regimen and overall bone health is paramount to both the discovery and treatment of these injuries, although diagnosis is often delayed in the setting of normal-appearing initial radiographs. While most stress fractures of the foot or ankle can usually be treated nonoperatively with a period of activity modification, fractures in certain locations are considered “high risk” due to poor intrinsic healing and may warrant more proactive operative management.

The Effect of Previous Methylphenidate Use on Incidence of Stress Fractures in Military Recruits: A Retrospective Cohort

BACKGROUND

Previous research has detected an increased risk of stress fractures among subjects who reported previous use of methylphenidate. Conversely, stimulant medication use has been associated with traumatic fracture risk reduction, possibly because of the improved control of the underlying symptoms of attention deficit hyperactivity disorder (ADHD). The goal of this study was to investigate the effect of previous methylphenidate use on the incidence of traumatic and stress fractures among combat soldiers with previously treated and untreated ADHD.

METHODS

The retrospective cohort included 100,000 combat soldiers recruited to the Israeli Defense Forces from 2005 through 2015. Diagnosis of ADHD and previous exposure to methylphenidate were determined on the basis of self-reported recruitment questionnaires and medical records. Accordingly, the cohort was divided into 3 groups: subjects with ADHD who were previously treated with methylphenidate (n = 689), untreated subjects with ADHD reporting no medication use (n = 762), and controls having no ADHD diagnosis (n = 98,549). Logistic regressions were fitted to determine the odds ratios (ORs) of study subjects for stress and non-stress (traumatic) fractures. Multivariate analysis incorporated baseline characteristics, including age, sex, weight, duration of service, and diagnosis of anemia, at some point during the service.

RESULTS

After adjustment for sex, anemia, weight, age, and duration of service, the risk of traumatic fractures was increased in both subjects with treated ADHD (OR, 1.03 [95% confidence interval (CI), 1.00 to 1.05]) and subjects with untreated ADHD (OR, 1.04 [95% CI, 1.02 to 1.07]) compared with controls. Subjects in the treated ADHD group were at a higher risk of stress fractures (OR, 1.04 [95% CI, 1.02 to 1.07]). Interestingly, a diagnosis of anemia was an independent predictor of stress fractures (OR, 1.05 [95% CI, 1.04 to 1.06]).

CONCLUSIONS

Methylphenidate use is associated with an increased risk of stress fractures but a decreased risk of traumatic fractures in individuals diagnosed with ADHD. These and previous findings may serve as sufficient basis for screening for other risk factors and perhaps taking prevention measures in all those using stimulant medications, especially those planning to engage in strenuous physical activity.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Association between stress fracture incidence and predicted body fat in United States Army Basic Combat Training recruits

Background

A stress fracture (SF) is a highly debilitating injury commonly experienced in United States Army Basic Combat Training (BCT). Body fat (BF) may be associated with this injury but previous investigations (in athletes) have largely used SF self-reports and lacked sufficient statistical power. This investigation developed an equation to estimate %BF and used that equation to examine the relationship between %BF and SF risk in BCT recruits.

Methods

Data for the %BF predictive equation involved 349 recruits with BF obtained from dual-energy X-ray absorptiometry. %BF was estimated using body mass index (BMI, weight/height²), age (yr), and sex in the entire population of BCT recruits over an 11-year period (n = 583,651). Medical information was obtained on these recruits to determine SF occurrence. Recruits were separated into deciles of estimated %BF and the risk of SFs determined in each decile.

Results

The equation was %BF = − 7.53 + 1.43 ● BMI + 0.13 ● age − 14.73 ● sex, with sex either 1 for men or 0 for women (r = 0.88, standard error of estimate = 4.2%BF). Among the men, SF risk increased at the higher and lower %BF deciles: compared to men in the mean %BF decile, the risk of a SF for men in the first (lowest %BF) and tenth (highest %BF) decile were 1.27 (95%confidence interval (95%CI) = 1.17–1.40) and 1.15 (95%CI = 1.05–1.26) times higher, respectively. Among women, SF risk was only elevated in the first %BF decile with risk 1.20 (95%CI = 1.09–1.32) times higher compared to the mean %BF decile.

Conclusions

Low %BF was associated with higher SF risk in BCT; higher %BF was associated with higher SF risk among men but not women.

Past Methylphenidate Exposure and Stress Fractures in Combat Soldiers: A Case-Control Study

BACKGROUND

Previous research has revealed decreased bone mineral density (BMD) among children and adolescents who receive methylphenidate (MP) treatment for attention deficit hyperactivity disorder (ADHD). These findings have major clinical implications given that the prevalence of medication-treated ADHD is on the rise worldwide. We decided to investigate the clinical effect of MP exposure on the incidence of stress fractures, for which a low BMD is a risk factor.

HYPOTHESIS

Exposure to MP is a risk factor for stress fractures.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

This is a case-control study of combat soldiers who served in the military for 3 years between 2005 and 2015. The case group included 2400 soldiers with at least 1 stress fracture diagnosed by a bone scan. The control group comprised 6187 combat soldiers without a diagnosis of a stress fracture. The use of MP was determined by an automated text search of medical records and manual sorting of the results. Other study variables included age; sex; weight; height; body mass index (BMI); place of birth; and characterization of fractures by location, side, and grade. Odds ratios of stress fractures, the attributable proportion among the exposed, and the population attributable fraction were calculated using standard contingency tables. Logistic regression was fitted after adjusting for covariates.

RESULTS

The previous use of MP was associated with a higher risk of stress fractures (odds ratio, 1.15 [95% CI, 1.07-1.24]). The attributable proportion was 13.2%, and the population attributable fraction was 0.3%. Logistic regression demonstrated an increased risk of stress fractures associated with past MP use, preserved after adjusting for BMI, sex, and place of birth ( P = .005). Female sex, BMI ≤20 kg/m², and 20 < BMI ≤25 kg/m² were independent positive predictors of a stress fracture, while African origin was a negative predictor. Most participants who used MP had only 1 fracture (77.8%), while the majority of participants who did not use MP in the past had ≥2 coincident fractures (53.5%) ( P = .003).

CONCLUSION

This study supports the hypothesis that an MP-associated reduction in BMD has a clinical effect in the form of an increased incidence of stress fractures. The high percentage of fractures attributed to MP use may serve as a basis for risk stratification, that is, the referral of patients with a history of MP use to BMD measurements.

Stress fracture of the second proximal phalanx of the foot in teenage athletes: Unrecognized location of stress fracture

Background

Adolescent athletes are a high-risk population for stress fractures. We report four cases of stress fractures of the second proximal phalanx, which had not been previously diagnosed as the location of the stress fracture of the foot, in teenage athletes.

Case report

All fractures were on the plantar side of the proximal phalangeal base, and the oblique images of the plain radiograph clearly depicted the fractures. Notably, three out of the four patients had histories of stress fracture of other locations. While three athletes with acute cases were able to make an early return to play with simple conservative management, the chronic case required surgical treatment for this rare injury.

Conclusion

Although a rare injury, it is important that clinicians be aware of this type of stress fracture, as a timely diagnosis can avoid the need for surgical treatment and allow an early return to play.

Development of a Prediction Model for Stress Fracture During an Intensive Physical Training Program: The Royal Marines Commandos

BACKGROUND

Stress fractures (SFs) are one of the more severe overuse injuries in military training, and therefore, knowledge of potential risk factors is needed to assist in developing mitigating strategies.

PURPOSE

To develop a prediction model for risk of SF in Royal Marines (RM) recruits during an arduous military training program.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

RM recruits (N = 1082; age range, 16-33 years) who enrolled between September 2009 and July 2010 were prospectively followed through the 32-week RM training program. SF diagnosis was confirmed from a positive radiograph or magnetic resonance imaging scan. Potential risk factors assessed at week 1 included recruit characteristics, anthropometric assessment, dietary supplement use, lifestyle habits, fitness assessment, blood samples, 25(OH)D, bone strength as measured by heel broadband ultrasound attention, history of physical activity, and previous and current food intake. A logistic least absolute shrinkage and selection operator (LASSO) regression with 10-fold cross-validation was used to select potential predictors among 47 candidate variables. Model performance was assessed using measures of discrimination (c-index) and calibration. Bootstrapping was used for internal validation of the developed model and to quantify optimism.

RESULTS

A total of 86 (8%) volunteer recruits presented at least 1 SF during training. Twelve variables were identified as the most important risk factors of SF. Variables strongly associated with SF were age, body weight, pretraining weightbearing exercise, pretraining cycling, and childhood intake of milk and milk products. The c-index for the prediction model, which represents the model performance in future volunteers, was 0.73 (optimism-corrected c-index, 0.68). Although 25(OH)D and VO₂max had only a borderline statistically significant association with SF, the inclusion of these factors improved the performance of the model.

CONCLUSION

These findings will assist in identifying recruits at greater risk of SF during training and will support interventions to mitigate this injury risk. However, external validation of the model is still required.

Risk of Stress Fracture Varies by Race/Ethnic Origin in a Cohort Study of 1.3 Million US Army Soldiers

Stress fractures (SF) are common and costly injuries in military personnel. Risk for SF has been shown to vary with race/ethnicity. Previous studies report increased SF risk in white and Hispanic Soldiers compared with black Soldiers. However, these studies did not account for the large ethnic diversity in the US military. We aimed to identify differences in SF risk among racial/ethnic groups within the US Army. A retrospective cohort study was conducted using data from the Total Army Injury and Health Outcomes Database from 2001 until 2011. SF diagnoses were identified from ICD-9 codes. We used Cox-proportional hazard models to calculate time to SF by racial/ethnic group after adjusting for age, education, and body mass index. We performed a sex-stratified analysis to determine whether the ethnic variation in SF risk depends on sex. We identified 21,549 SF cases in 1,299,332 Soldiers (more than 5,228,525 person-years of risk), revealing an overall incidence rate of 4.12 per 1000 person-years (7.47 and 2.05 per 1000 person-years in women and men, respectively). Using non-Hispanic blacks as the referent group, non-Hispanic white women had the highest risk of SF, with a 92% higher risk of SF than non-Hispanic black women (1.92 [1.81-2.03]), followed by American Indian/Native Alaskan women (1.72 [1.44-1.79]), Hispanic women (1.65 [1.53-1.79]), and Asian women (1.32 [1.16-1.49]). Similarly, non-Hispanic white men had the highest risk of SF, with a 59% higher risk of SF than non-Hispanic black men (1.59 [1.50-1.68]), followed by Hispanic men (1.19 [1.10-1.29]). When examining the total US Army population, we found substantial differences in the risk of stress fracture among racial/ethnic groups, with non-Hispanic white Soldiers at greatest risk and Hispanic, American Indian/Native Alaskan, and Asian Soldiers at an intermediate risk. Additional studies are needed to determine the factors underlying these race- and ethnic-related differences in stress fracture risk. © 2017 American Society for Bone and Mineral Research.

Association Between Single Gene Polymorphisms and Bone Biomarkers and Response to Calcium and Vitamin D Supplementation in Young Adults Undergoing Military Training

Initial military training (IMT) is associated with increased stress fracture risk. In prior studies, supplemental calcium (Ca) and vitamin D provided daily throughout IMT reduced stress fracture incidence, suppressed parathyroid hormone (PTH), and improved measures of bone health compared with placebo. Data were analyzed from a randomized, double-blind, placebo-controlled trial to determine whether single-nucleotide polymorphisms (SNPs) in Ca and vitamin D-related genes were associated with circulating biomarkers of bone metabolism in young adults entering IMT, and whether responses to Ca and vitamin D supplementation were modulated by genotype. Associations between SNPs, including vitamin D receptor (VDR), vitamin D binding protein (DBP), and 1-alpha-hydroxylase (CYP27B1), and circulating biomarkers were measured in fasting blood samples from volunteers (n = 748) starting IMT. Volunteers were block randomized by race and sex to receive Ca (2000 mg) and vitamin D (1000 IU) or placebo daily throughout Army or Air Force IMT (7 to 9 weeks). Total Ca and vitamin D intakes were calculated as the sum of supplemental intake based on intervention compliance and dietary intake. Relationships between SNPs, Ca, and vitamin D intake tertile and change in biomarkers were evaluated in trial completers (n = 391). At baseline, the minor allele of a DBP SNP (rs7041) was positively associated with both 25OHD (B = 4.46, p = 1.97E-10) and 1,25(OH)₂ D₃ (B = 9.63, p < 0.001). Combined genetic risk score (GRS) for this SNP and a second SNP in the VDR gene (rs1544410) was inversely associated with baseline 25OHD (r = -0.28, p < 0.001) and response to Ca and vitamin D intake differed by GRS (p < 0.05). In addition, presence of the minor allele of a second VDR SNP (rs2228570) was associated with lower P1NP (B = -4.83, p = 0.04) and osteocalcin (B = -0.59, p = 0.03). These data suggest that VDR and DBP SNPs are associated with 25OHD status and bone turnover and those with the highest GRS require the greatest vitamin D intake to improve 25OHD during IMT. © 2016 American Society for Bone and Mineral Research.

Comparison of Site-Specific Bone Mineral Densities between Endurance Runners and Sprinters in Adolescent Women

We aimed to compare site-specific bone mineral densities (BMDs) between adolescent endurance runners and sprinters and examine the relationship of fat-free mass (FFM) and nutrient intake on BMD. In this cross-sectional study, 37 adolescent female endurance runners and sprinters (16.1 ± 0.8 years) were recruited. BMD and FFM were assessed by dual-energy X-ray absorptiometry. Nutrient intake and menstrual state were evaluated by questionnaires. After adjusting for covariates, spine and total bone less head (TBLH) BMDs were significantly higher in sprinters than endurance runners (TBLH, 1.02 ± 0.05 vs. 0.98 ± 0.06 g/cm²; spine, 0.99 ± 0.06 vs. 0.94 ± 0.06 g/cm²; p < 0.05). There was no significant difference between groups in other sites. The rate of menstrual abnormality was higher in endurance runners compared with sprinters (56.3% vs. 23.8%; p < 0.05). FFM was a significant covariate for BMD on all sites except the spine (p < 0.05). Dietary intake of vitamin D was identified as a significant covariate only for pelvic BMD (p < 0.05). The BMDs of different sites among endurance runners and sprinters were strongly related to FFM. However, the association of FFM with spine BMD cannot be explained by FFM alone. Other factors, including nutrition and/or mechanical loading, may affect the spine BMD.

Prospective cohort study of the risk factors for stress fractures in Chinese male infantry recruits

Objective

To determine potential risk factors that could predict stress fractures over an 8-week basic military training in Chinese male infantry recruits.

Methods

Recruits from three infantry units enrolled in this prospective study. At baseline, demographic data, personal history of stress fractures, mean duration of weekly exercise and smoking history were recorded on questionnaires and blood samples taken for analysis of bone turnover biomarkers and genetic factors.

Results

Of the 1516 male recruits who volunteered to participate in the study, 1398 recruits provided data for analysis. In total, 189 stress fracture cases were observed (incidence rate: 13.5%) during the 8-week training period. Recruits with stress fractures had a significantly higher incidence of prior fracture history and lower exercise level prior to enrolment compared with those without stress fractures. A significant difference in both allelic frequency and genotypic distribution of the growth differentiation factor 5 (GDF5) gene rs143383 polymorphism was observed between recruits with and without stress fractures. However, no difference in serum bone turnover biomarkers was detected between groups.

Conclusion

This prospective, cohort study indicates that fracture history, lower exercise level and GDF5 rs143383 may be predictive risk factors for stress fractures in Chinese male infantry recruits.

Evaluating the Risk of a Fifth Metatarsal Stress Fracture by Measuring the Serum 25-Hydroxyvitamin D Levels

BACKGROUND

The fifth metatarsal bone is a common site of stress fractures in soccer athletes. Although several endocrine risk factors for stress fractures have been proposed, the endocrine risks for fifth metatarsal (5-MT) stress fractures have not been evaluated.

METHODS

To evaluate the endocrine risks of fifth metatarsal stress fractures, we conducted a cumulative case-control study. The present study included 37 athletes, of which 18 had a history of a zone 2 or zone 3 fifth metatarsal stress fracture and 19 controls. We analyzed serum 25-hydroxyvitamin D (25-OHD), serum parathyroid hormone (PTH), as well as biochemical markers of bone turnover by univariate or multivariate analyses.

RESULTS

Logistic regression analyses adjusted for multiple confounders revealed that insufficient serum 25-OHD levels less than 30 ng/mL (odds ratio [OR], 23.3), higher serum PTH levels (OR, 1.01), or higher serum bone-specific isoform of alkaline phosphatase levels (OR, 1.10) rather than serum tartrate-resistant acid phosphatase 5b were associated with statistically significantly increased odds of 5-MT stress fractures. A postestimation calculation demonstrated that 25-OHD levels of 10 and 20 ng/mL were associated with 5.1 and 2.9 times greater odds for 5-MT stress fractures, respectively.

CONCLUSION

25-OHD insufficiency was associated with an increased incidence of 5-MT stress fractures. This insight may be useful for intervening to prevent 5-MT stress fractures.

LEVEL OF EVIDENCE

Level III, case-control study.

Musculoskeletal manifestations of the antiphospholipid syndrome

The scope of clinical and laboratory manifestations of the antiphospholipid syndrome (APS) has increased dramatically since its discovery in 1983, where any organ system can be involved. Musculoskeletal complications are consistently reported in APS patients, not only causing morbidity and mortality, but also affecting their quality of life. We reviewed all English papers on APS involvement in the musculoskeletal system using Google Scholar and Pubmed; all reports are summarized in a table in this review. The spectrum of manifestations includes arthralgia/arthritis, avascular necrosis of bone, bone marrow necrosis, complex regional pain syndrome type-1, muscle infarction, non-traumatic fractures, and osteoporosis. Some of these manifestations were reported in good quality studies, some of which showed an association between aPL-positivity and the occurrence of these manifestations, while others were merely described in case reports.

Low serum 25-hydroxyvitamin D is associated with increased risk of stress fracture during Royal Marine recruit training

The aim of this study was to investigate vitamin D status and stress fracture risk during Royal Marine military training. Poor vitamin D status was associated with an increased risk of stress fracture. Vitamin D supplementation may help to reduce stress fracture risk in male military recruits with low vitamin D status.

INTRODUCTION

Stress fracture is a common overuse injury in military recruits, including Royal Marine (RM) training in the UK. RM training is recognised as one of the most arduous basic training programmes in the world. Associations have been reported between serum 25-hydroxyvitamin D (25(OH)D) and risk of stress fracture, but the threshold of 25(OH)D for this effect remains unclear. We aimed to determine if serum 25(OH)D concentrations were associated with stress fracture risk during RM training.

METHODS

We prospectively followed 1082 RM recruits (males aged 16-32 years) through the 32-week RM training programme. Troops started training between September and July. Height, body weight and aerobic fitness were assessed at week 1. Venous blood samples were drawn at weeks 1, 15 and 32. Serum samples were analysed for 25(OH)D and parathyroid hormone (PTH).

RESULTS

Seventy-eight recruits (7.2 %) suffered a total of 92 stress fractures. Recruits with a baseline serum 25(OH)D concentration below 50 nmol L(-1) had a higher incidence of stress fracture than recruits with 25(OH)D concentration above this threshold (χ(2) (1) = 3.564, p = 0.042; odds ratio 1.6 (95 % confidence interval (CI) 1.0-2.6)). Baseline serum 25(OH)D varied from 47.0 ± 23.7 nmol L(-1) in February, to 97.3 ± 24.6 nmol L(-1) in July (overall mean 69.2 ± 29.2 nmol L(-1), n = 1016). There were weak inverse correlations between serum 25(OH)D and PTH concentrations at week 15 (r = -0.209, p < 0.001) and week 32 (r = -0.214, p < 0.001), but not at baseline.

CONCLUSION

Baseline serum 25(OH)D concentration below 50 nmol L(-1) was associated with an increased risk of stress fracture. Further studies into the effects of vitamin D supplementation on stress fracture risk are certainly warranted.

Stress fractures: definition, diagnosis and treatment

Stress fractures were first described in Prussian soldiers by Breithaupt in 1855. They occur as the result of repeatedly making the same movement in a specific region, which can lead to fatigue and imbalance between osteoblast and osteoclast activity, thus favoring bone breakage. In addition, when a particular region of the body is used in the wrong way, a stress fracture can occur even without the occurrence of an excessive number of functional cycles. The objective of this study was to review the most relevant literature of recent years in order to add key information regarding this pathological condition, as an updating article on this topic.

A THREE-DIMENSIONAL MORPOLOGICAL MEASUREMENT AND IN VITRO BIOMECHANICAL STUDY OF METATARSALS

Stress fracture of the metatarsal (MT) is often reported clinically. This study was aimed to measure and compare the three-dimensional (3D) morphological structure of five MTs, and investigate the in vitro biomechanics of five MTs under simulated stance phase. A total of seven foot-ankle samples of human cadavers were collected for this experiment. All samples were CT-scanned and 3D re-constructed for digital measurements. To simulate the stance phase, each sample was vertically loaded with 700-N through a material testing machine. The 3D-reconstruction-based measurement showed significant differences of the shaft length, vertical height, and inclination angle between the second MT and four others. Experimental strain measurements at dorsal MTs along the principal axis are all compressive. The values are respectively [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] micro-strain from the first to fifth MTs. This study proposed a new load condition of plantar-flexed simply supported beam to describe the MT loading mechanism. The second and third MTs have higher risk of stress fracture due to combined effects of inhomogeneous load distribution, unfavorable geometry and structure, and limited joint motion. This finding would be helpful for design of protective equipment.

Serum 25-Hydroxyvitamin D Levels and Stress Fractures in Military Personnel: A Systematic Review and Meta-analysis

BACKGROUND

Low serum 25-hydroxyvitamin D (25(OH)D) levels have been associated with stress fractures in various physically active populations such as the military.

PURPOSE

To examine the association between serum 25(OH)D levels and stress fractures in the military.

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

Relevant studies were identified through searching multiple databases and manually screening reference lists. Two reviewers independently selected the included studies by applying the eligibility criteria to the title, abstract, and/or full text of the articles yielded in the search. Two reviewers also independently conducted the methodological quality assessment and data extraction. A random-effects model was used to calculate the mean difference (MD) with 95% CI in serum 25(OH)D levels between stress fracture cases and controls.

RESULTS

Nine observational studies on lower extremity stress fractures were eligible, and 1 was excluded due to inadequate data. A total of 2634 military personnel (age, 18-30 years; 44% male) with 761 cases (16% male) and 1873 controls (61% male) from 8 studies were included in the analysis. Three of the 8 studies measured serum 25(OH)D levels at the time of stress fracture diagnosis, and the 5 remaining studies measured serum 25(OH)D levels at the time of entry into basic training. The mean serum 25(OH)D level was lower in stress fracture cases than in controls at the time of entry into basic training (MD, -2.63 ng/mL; 95% CI, -5.80 to 0.54; P = .10; I(2) = 65%) and at the time of stress fracture diagnosis (MD, -2.26 ng/mL; 95% CI, -3.89 to -0.63; P = .007; I(2) = 42%).

CONCLUSION

Despite the inherent limitations of the included studies, the study results suggest some association between low serum 25(OH)D levels and lower extremity stress fractures in military personnel. Given the rigorous training of military personnel, implementing strategies to ensure sufficient 25(OH)D levels may be beneficial for reducing the risk of stress fractures.

[Epidemiological aspects of limb fractures related to military exercises in Togo]

Le but de notre étude était de déterminer la fréquence des fractures de membres liées à l'exercice de la fonction militaire au sein des Forces de Défense et de Sécurité en milieu africain en vue de ressortir l'impact des différentes circonstances de survenue. Nous avons entrepris une étude rétrospective descriptive allant du 1er janvier 2004 au 31 décembre 2013. Elle a concerné les agents des forces de défense et de sécurité traités pour des fractures de membres au cours de cette période. Sept cent quatre (704) cas de fractures de membres ont été dénombrés. L’âge moyen des patients était de 30,57 ans avec des extrêmes de 19 et 55 ans. La prédominance masculine était nette (95,71%). L'Armée de Terre (51,05%) et la Gendarmerie Nationale (38,86%) étaient les plus représentées. Les hommes du rang étaient majoritaires (43,08%), suivis des sous-officiers (32,59%). La fréquence annuelle des fractures de membres en rapport avec la profession militaire était de 63 cas. Les fractures de jambe étaient les lésions les plus recensées (32,96%). Les Formations et les stages militaires ont été les circonstances de survenue les plus rencontrées (42,60%), suivies des accidents de la circulation (39,43%). La perte des journées de service liée à ces lésions était estimée à 14009 jours par an. Les fractures de jambes occupent le premier rang des fractures de membres en rapport avec l'exercice de la profession militaire. Les formations-stages militaires et les accidents de la voie publique en sont les deux grandes circonstances de survenue.

Novel candidate genes putatively involved in stress fracture predisposition detected by whole-exome sequencing

While genetic factors in all likelihood contribute to stress fracture (SF) pathogenesis, a few studies focusing on candidate genes have previously been reported. The objective of this study is to gain better understanding on the genetic basis of SF in a gene-naive manner. Exome sequence capture followed by massive parallel sequencing of two pooled DNA samples from Israeli combat soldiers was employed: cases with high grade SF and ethnically matched healthy controls. The resulting sequence variants were individually verified using the Sequenom™ platform and the contribution of the genetic alterations was validated in a second cohort of cases and controls. In the discovery set that included DNA pool of cases (n = 34) and controls (n = 60), a total of 1174 variants with >600 reads/variant/DNA pool were identified, and 146 (in 127 genes) of these exhibited statistically significant (P < 0·05) different rates between SF cases and controls after multiple comparisons correction. Subsequent validation of these 146 sequence variants individually in a total of 136 SF cases and 127 controls using the Sequenom™ platform validated 20/146 variants. Of these, three missense mutations (rs7426114, rs4073918, rs3752135 in the NEB, SLC6A18 and SIGLEC12 genes, respectively) and three synonymous mutations (rs2071856, rs2515941, rs716745 in the ELFN2, GRK4, LRRC55 genes) displayed significant different rates in SF cases compared with controls. Exome sequencing seemingly unravelled novel candidate genes as involved in SF pathogenesis and predisposition.