Michael R. Boivin

Risk factors for back-related disability in the US Army and Marine Corps.

Study Design. Matched case-control epidemiological study. Objective. To identify pre-enlistment, demographic, and service-related risk factors for back-related disability in enlisted US soldiers and Marines comparing those who were deployed with those who did not deploy during the service term. Summary of Background Data. Back conditions are a major cause of morbidity and lost work days in both the US working population and military. Back-related conditions are among the most prevalent causes of military disability discharge but little research has been conducted to identify risk factors for back-related disabilities in this population. Methods. Cases included enlisted Army and Marine Corps service members evaluated for back-related disability. Controls, frequency matched by year of military entrance and service, were selected from the enlisted service member population. Pre-enlistment demographic and medical characteristics, deployment, and ambulatory care data collected from existing military databases were used. Crude and adjusted odds of back-related disability were modeled using conditional logistic regression. Results. In adjusted models, service members who were overweight (odds ratio [OR]: 1.17; 95% confidence interval [95% CI]: 1.12–1.23) and obese (OR: 1.35; 95% CI: 1.26–1.44), between ages 25 and 29 years (OR: 1.23; 95% CI: 1.16–1.31), or 30 years or older (OR: 1.43; 95% CI: 1.34–1.52) at military entrance were at increased odds of a back-related disability. History of a back diagnosis at the pre-enlistment medical examination (OR: 1.94; 95% CI: 1.50–2.50) and deploying once (OR: 1.09; 95% CI: 1.05–1.14) were also associated with increased odds of a back-related disability. Conclusion. Enlisted soldiers and marines with back-related disabilities were more likely to be older, have a higher body mass index, have a history of pre-enlistment back conditions, and were deployed once, compared with controls without a back-related disability. Additional research is necessary to further examine the complex relationship between deployment to combat zones, onset of musculoskeletal symptoms, and back-related disability in soldiers and marines. Level of Evidence: 4

Meta-analysis of Cigarette Smoking and Musculoskeletal Injuries in Military Training

Purpose Tobacco use is common among military personnel, as is musculoskeletal injury during training. In a review of the literature on musculoskeletal injuries, there was mixed evidence on the role of smoking as a risk factor. The purpose of this study is to review and analyze the literature on the impact of cigarette smoking on lower-extremity overuse injuries in military training. Methods We performed a literature search on articles published through October 2016. Search terms focused on lower-extremity overuse musculoskeletal injuries and cigarette smoking in military populations. We conducted a meta-analysis overall and by sex, including smoking intensity. Results We identified 129 potential studies and selected 18 based on quality. The overall rate ratio for smoking was 1.31, 1.31 for men, and 1.23 for women. Overall and for each sex, rate ratios were significantly greater than 1.0 for each intensity level of smoking. Conclusions Smoking is a moderate risk factor for musculoskeletal injury and may account for a meaningful proportion of injuries among men and women due to the high prevalence of smoking and injury in this population. Although enlistees are not allowed to smoke during basic training, their risk of injury remains high, indicating that smokers may remain at increased risk for medium- to long-term duration.

Epidemiology of asthma-related disability in the U.S. Armed Forces: 2007–2012

Abstract Objective: To characterize the demographic, disability and deployment characteristics of U.S. Armed Forces personnel with an asthma-related disability discharge, which includes separation (without benefits) and retirement (with disability benefits). Methods: Incidence rates for personnel evaluated for disability discharge and/or disability retired due to asthma and due to all other causes of disability discharge were calculated per 100,000 active duty enlisted service members by year. Multivariate logistical regression was used to examine the associations between disability retirement and several demographic and disability characteristics of service members evaluated for asthma-related disability discharge versus those evaluated for any other non-respiratory condition for each branch of military service. Results: Service members evaluated for disability discharge related to asthma most often do not have comorbidity and are disability retired rather than separated, with rates of disability retirement increasing over time. Groups with a significantly higher incidence of evaluation for asthma-related disability include females, individuals who entered the military prior to the age of 20, non-Whites, and those with a history of deployment to Iraq or Afghanistan. The characteristic most associated with the odds of disability retirement was a history of deployment. Conclusions: New-onset asthma occurring after military entry often causes occupational impairment in service members, especially in those that have been deployed to Iraq or Afghanistan.

Predictors of the Onset of Schizophrenia in US Military Personnel.

Abstract Alterations in immune response may be an important component in the etiopathogenesis of schizophrenia and bipolar disorder. We examined the associations of pentraxin-3 (PTX3) with the onset of schizophrenia or bipolar disorder. We tested preonset serum specimens from 160 US military service members who were later diagnosed with schizophrenia or bipolar disorder and 160 matched controls without psychiatric disorders. Lower serum levels of PTX3 were predictive of schizophrenia but not of bipolar disorder. Subjects with below-median PTX3 levels had a 3.0 odds ratio (confidence interval, 1.6–5.7) for schizophrenia onset in the multivariable logistic regression model controlling for demographic and military variables. The test for trends was significant (p = 0.002), with the likelihood increasing as the levels of PTX3 decreased. Crude and adjusted categorized levels were not predictive of bipolar disorder. A lower level of inflammatory response indicated by PTX3 might be implicated in developing schizophrenia.

Epidemiology of psychiatric disability without posttraumatic stress disorder among U.S. Army and Marine Corps personnel evaluated for disability discharge.

Psychiatric disorders are a common reason for disability discharge from the U.S. military. Research on psychiatric disorders in military personnel evaluated for disability discharge has historically focused on posttraumatic stress disorder (PTSD), yet 40% of service members evaluated for a psychiatric-related disability do not have PTSD. This studys objective was to describe characteristics and correlates of disability in Army and Marine Corps personnel diagnosed with psychiatric disorders other than PTSD. In this cross-sectional study, the chi-square and Wilcoxon-Mann-Whitney tests compared the distribution of demographic, disability and deployment characteristics between those evaluated for non-PTSD psychiatric disability (N = 9125) versus those evaluated for any other non-psychiatric condition (N = 78,072). Multivariate logistic regression examined associations between disability retirement and demographic and disability characteristics. Results show a significantly higher prevalence of disability retirement, deployment, and comorbidity among Army and Marine Corps personnel evaluated for disability discharge related to a non-PTSD psychiatric disorder. Mood disorders, anxiety disorders and dementia were the most commonly evaluated psychiatric disorders. Characteristics associated with increased odds of non-PTSD psychiatric-related disability retirement includes being in the Marine Corps (OR = 1.24), being black (OR = 1.29) or other race (OR = 1.33), having a combat-related condition (OR = 2.50), and older age. Service members evaluated for a non-PTSD psychiatric disability have similar rates of disability retirement as those evaluated for PTSD, suggesting non-PTSD psychiatric disorders cause a severe and highly compensated disability. Additional research is needed describing the epidemiology of specific non-PTSD psychiatric disorders, such as depression, in service members evaluated for disability discharge.

Epidemiology of Major Depressive Disorder Disability in the US Military: FY 2007–2012

Abstract This study assesses the incidence of major depressive disorder (MDD) disability discharge and retirement in the Army, Navy, Marine Corps and Air Force and describes MDD comorbidity. Service members with a disability discharge for either MDD (n = 2,882) or any nonpsychiatric disability (n = 56,145), between fiscal years 2007 and 2012, were included in the study population. Those with MDD disability at first evaluation but not at last evaluation were excluded. The incidence of MDD disability discharge increased significantly in the Army and Air Force between fiscal years 2007 and 2012. MDD disability retirement significantly increased in the Army, Navy, and Air Force. Females, and those who experienced at least one deployment, had higher incidence rates of MDD disability discharge. All services included spinal diseases and posttraumatic stress disorder in their top five comorbid categories. Given the association between trauma and MDD, further research into the role of both combat exposure and injury on MDD is merited.

Preenlistment and early service risk factors for traumatic brain injury in the Army and Marine Corps: FY 2002-2010

Objective: To determine the preenlistment and early service risk factors for traumatic brain injury (TBI)-related disability in Army and Marine Corps service members. Design: Matched case-control design. Main Outcome: TBI disability discharges. Subjects: Army and Marine Corps service members with an enlistment record and disability discharge for TBI were included as cases. Controls were selected from the enlisted population with no disability evaluation record and were matched on fiscal year of enlistment, sex, and service at a ratio of 5:1. Results: Older age at enlistment resulted in a significantly increased risk for TBI disability in the crude and adjusted models (adjusted odds ratio [aOR] = 1.49; 95% confidence interval [CI], 1.16-1.91). An enlistment military occupational specialty (MOS) with a combat arms designation resulted in an almost 3-fold increased odds of TBI disability compared with other MOS categories (aOR = 2.75; 95% CI, 2.46-3.09). This remained a significant risk factor for TBI disability in the multivariate model (aOR = 2.74; 95% CI, 2.45-3.08). Conclusion: Results from this study help inform the existing body of military TBI research by highlighting the preenlistment demographic and early service risk factors for TBI disability. Further research into the role of age on TBI disability in the military is merited.

Excess Stress Fractures, Musculoskeletal Injuries, and Health Care Utilization Among Unfit and Overweight Female Army Trainees

Background: Musculoskeletal injuries are prevalent among military trainees and certain occupations. Fitness and body mass index (BMI) have been associated with musculoskeletal conditions, including stress fractures. Hypothesis: The incidence of, and excess health care utilization for, stress fracture and non–stress fracture overuse musculoskeletal injuries during the first 6 months of service is higher among unfit female recruits. Those who exceeded body fat limits are at a greater risk of incident stress fractures, injuries, or health care utilization compared with weight-qualified recruits. Study Design: Cohort study; Level of evidence, 3. Methods: All applicants to the United States Army were required to take a preaccession fitness test during the study period (February 2005–September 2006). The test included a 5-minute step test scored as pass or fail. BMI was recorded at application. There were 2 distinct comparisons made in this study: (1) between weight-qualified physically fit and unfit women and (2) between weight-qualified physically fit women and those who exceeded body fat limits. We compared the incidence of, and excess health care utilization for, musculoskeletal injuries, including stress fractures and physical therapy visits, during the first 183 days of military service. Results: Among the weight-qualified women, unfit participants had a higher non–stress fracture injury incidence and related excess health care utilization rate compared with fit women, with rate ratios of 1.32 (95% CI, 1.14-1.53) and 1.18 (95% CI, 1.10-1.27), respectively. Among fit women, compared with the weight-qualified participants, those exceeding body fat limits had higher rate ratios for non–stress fracture injury incidence and related excess health care utilization of 1.27 (95% CI, 1.07-1.50) and 1.20 (95% CI, 1.11-1.31), respectively. Weight-qualified women who were unfit had a higher incidence of stress fractures and related excess health care utilization compared with fit women, with rate ratios of 1.62 (95% CI, 1.19-2.21) and 1.22 (95% CI, 1.10-1.36), respectively. Among fit women exceeding body fat limits, the stress fracture incidence and related excess health care utilization rate ratios were 0.79 (95% CI, 0.49-1.28) and 1.44 (95% CI, 1.20-1.72), respectively, compared with those who were weight qualified. Conclusion: The results indicate a significantly increased risk of musculoskeletal injuries, including stress fractures, among unfit recruits and an increased risk of non–stress fracture musculoskeletal injuries among recruits who exceeded body fat limits. Once injured, female recruits who were weight qualified but unfit and those who were fit but exceeded body fat limits had increased health care utilization. These findings may have implications for military accession and training policies as downsizing of military services will make it more important than ever to optimize the health and performance of individual service members.

Fitness, obesity and risk of asthma among Army trainees

BACKGROUND Epidemiological data suggest an association between overweight/obesity and asthma. However, less is known about the relationship between physical fitness and asthma. AIMS To enumerate new-onset asthma diagnoses in Army recruits during the first 2 years of service and determine associations with fitness and excess body fat (EBF) at military entrance. METHODS New asthma diagnoses over 2 years in Army recruits at six entrance stations were obtained from military health and personnel records. Poisson regression models were used to determine associations of asthma diagnosis with pre-accession fitness testing, EBF and other potential factors. RESULTS In 9979 weight-qualified and 1117 EBF entrants with no prior history of asthma, 256 new cases of asthma were diagnosed within 2 years of military entry. Low level of fitness, defined by a step test and EBF, was significantly associated with new asthma diagnosis [adjusted incidence rate ratio (IRR), 1.47; 95% confidence interval (CI) 1.11-1.96 and adjusted IRR, 1.53; 95% CI 1.06-2.20, respectively]. CONCLUSIONS Individuals with low fitness levels, EBF or both are at higher risk of asthma diagnosis in the first 2 years of military service.

Revealing Facts and Avoiding Biases: A Review of Several Common Problems in Statistical Analyses of Epidemiological Data.

This paper reviews several common challenges encountered in statistical analyses of epidemiological data for epidemiologists. We focus on the application of linear regression, multivariate logistic regression, and log-linear modeling to epidemiological data. Specific topics include: (a) deletion of outliers, (b) heteroscedasticity in linear regression, (c) limitations of principal component analysis in dimension reduction, (d) hazard ratio vs. odds ratio in a rate comparison analysis, (e) log-linear models with multiple response data, and (f) ordinal logistic vs. multinomial logistic models. As a general rule, a thorough examination of a model’s assumptions against both current data and prior research should precede its use in estimating effects.