Gender differences in limited duty time for lower limb injury

Gender differences in limited duty time for lower limb injury Abstract Background Among active-duty military personnel, lower limb musculoskeletal injuries and related conditions (injuries) frequently arise as unintended consequences of physical training. These injuries are particularly common among women. The practical impact of such injuries on temporary military occupational disability has not been estimated with precision on a large scale. Aims To determine the proportion of service time compromised by limited duty days attributable to lower limb injuries, characterize the time affected by these limitations in terms of specific lower limb region and compare the limited duty time between male and female soldiers. Methods Administrative data and individual limited duty assignments (profiles) were obtained for active-duty US Army personnel who served in 2014. Lower limb injury-related profiles were used to calculate the percent of person-time requiring duty limitations by gender and body region. Results The study group was 568 753 soldiers of whom 14% were women. Nearly 13% of service days for active-duty US Army soldiers required limited duty for lower limb injuries during 2014. Knee injuries were responsible for 45% of those days. Within integrated military occupations, female soldiers experienced 27–57% more time on limited duty for lower limb injuries compared with men. Conclusions The substantial amount of limited duty for lower limb musculoskeletal injuries among soldiers highlights the need for improvement in training-related injury screening, prevention and timely treatment with particular attention to knee injuries. The excessive impact of lower limb injuries on female soldiers’ occupational functions should be a surveillance priority in the current environment of expanding gender-integrated training. Injury, military, musculoskeletal, women Introduction For active-duty US Army soldiers, regular physical training is a critical daily job function. Common unintended consequences of this training include lower limb musculoskeletal injuries and injury-related conditions. Within an otherwise healthy and carefully-screened young adult population, injuries of all types required over 750 000 medical visits for the approximately 360 000 person-years of non-deployed service time for the active-duty US Army in 2006 [1]. Half of these visits were attributable to lower limb overuse injuries such as stress fractures, Achilles tendonitis and plantar fasciitis [1]. Prior cross-sectional studies have estimated that lower limb injuries and related conditions require millions of days per year of limited duty for the active-duty US military [2,3]. The proportion of service time requiring injury-related limited duty provides a practical metric of the impact of injuries on job function, with implications for losses in unit productivity and deployment readiness. Accurate measures of limited duty are necessary in planning for military operations, evaluating training regimens from a risk-benefit perspective, and prioritizing prevention efforts. Because limited-duty days are not systematically recorded in the outpatient record, past studies have relied upon average civilian recovery times and retrospective surveys of service members to approximate days of limited duty [2–4]. There have been no large studies of limited duty associated with lower limb musculoskeletal injury as defined by ‘profiles.’ US Army clinicians use profiles to (i) record the nature, severity, duration and medical reasons for a soldier’s inability to fulfil his or her occupational requirements and (ii) to communicate these limitations to the soldier’s commander. Profiles may be assigned as temporary to cover short-term recovery periods for injuries or illnesses, or permanent to reflect conditions requiring chronic duty limitations. Studying profiles is essential when defining limited duty because these formal assignments represent the gold standard for a soldier’s functional status in US Army medical records. The electronic system for recording profiles, eProfile, constitutes a rich dataset that can be used to assess the annual proportion of service time compromised by limited duty. These data provide detail on the medical reasons for limited duty and the degree and duration of limitation. Prior studies have also not compared rates of limited duty for lower limb injuries between men and women. Female soldiers and trainees appear more susceptible to injuries than males, both in general [4–9] and for a broad range of specific lower limb injuries including stress fractures [6,10], medial tibial stress syndrome [11] and patellofemoral pain syndrome [12]. Therefore, it is likely that lower limb injuries and related conditions require more duty limitations for women than for men. Further, variability among different military occupations with respect to job responsibilities, physical training and culture may differentially affect the injury and limited duty rates for men and women [13,14]. The importance of assessing any gender-based risk difference is only increasing as all positions in the US armed forces are now open to women [15]. We therefore analysed temporary and permanent profiles for all soldiers serving on active duty in the US Army during calendar year 2014 to: (i) determine the proportion of service time compromised by limited duty days attributable to lower limb musculoskeletal injuries and related conditions, (ii) characterize the time affected by these limitations in terms of specific lower limb region and (iii) compare the proportion of limited duty experienced by men and women. Methods For this cross-sectional study, we utilized data from the Stanford Military Data Repository, a longitudinal dataset organized at the person-month level on the active-duty US Army population. Available data included demographic characteristics, military occupation, time spent in service and profiles containing duty restrictions assigned by clinicians to individual soldiers. All soldiers serving on active duty at any point in 2014 were initially deemed eligible for inclusion. However, because exploratory data analysis revealed that digital profiles in the eProfile system were seldom used to record limited duty days during basic combat training (BCT), the first 3 months of service for new soldiers were not included in this analysis. Additionally, the person-months spent on combat deployment (6% of the total available) and the profile assignments made during those months were excluded from this analysis, because duty limitations during combat may occur due to different problems than during training and may be addressed and documented differently. Finally, we excluded soldiers with inconsistently recorded gender, which likely reflected data entry errors because openly transgender persons were not permitted to serve in the US Army in 2014. The primary predictor of interest was gender. Other covariates were age (≤20, 21–30, 31–40 or >40), year of service entry (pre-2011, 2011, 2012 or 2013–14), pay grade (officer or enlisted) and broad category of military occupation for enlisted personnel. The primary outcome for this analysis was the proportion of service days during calendar year 2014 with limited duty indicated by any temporary or permanent profile attributable to a lower limb musculoskeletal injury or related condition (injury). Lower limb regions included were the hip, thigh, knee, lower leg, ankle and foot. The lower back was not included. Our injury definition included inflammation and pain, tendonitis, fasciitis, joint derangement, dislocation, stress injury/fracture, sprain, strain, and rupture, and excluded contusions, crushes, wounds, and infections. According to the US Army profile system, temporary profiles are designated for a specific number of days, while permanent profiles are assigned with no expiration date and are re-evaluated at annual periodic health assessments [16]. Each profile includes a numeric score for each of six body regions, one of which is lower extremity. A score of 1 indicates full capacity, and scores of 2, 3 or 4 indicate progressively greater functional limitations. Each profile also includes a medical condition text field where the clinician records the reason(s) for limited duty using common terminology. For this analysis, we included those profiles with a lower extremity limitation score of 2, 3 or 4 that also denoted lower limb injury in the medical condition text field, based on key terms derived from our injury definition (the key terms are listed in Supplementary Section 1, available at Occupational Medicine Online). Profiles listing multiple medical reasons were included if any of the reasons was lower limb injury. We classified these profiles into six mutually exclusive body region categories: hip/thigh, knee, lower leg/ankle, foot, multiple lower limb regions and unspecified lower limb. The full classification algorithms and accuracy assessments are described in Supplementary Section 1 (available at Occupational Medicine Online) and sample medical conditions classified within each body region are shown in Supplementary Table 1 (available at Occupational Medicine Online). The classification algorithm used to identify profiles attributable to lower limb injury demonstrated strong accuracy in comparison to clinician assessment of profile reason from the medical condition, with a sensitivity of 98%, specificity of 93%, negative predictive value of 95% and positive predictive value of 96%. This set of profiles was used to calculate the number of limited-duty days and proportion of service time on limited duty for each soldier for each body region (details are in Supplementary Section 2, available at Occupational Medicine Online). These proportions were aggregated by gender and for the full population by summing the total number of limited-duty days and dividing by the total number of service days. Secondary analyses stratified these calculations by pay grade and military occupation to examine potential confounding. To illustrate the main types of activity restrictions entailed by the profiles, we summarized the proscribed activities noted in pre-specified fields and in the text field for clinician comments. Details on this descriptive analysis are given in Supplementary Section 3 (available at Occupational Medicine Online). We conducted two sensitivity analyses. First, to examine the impact of including profiles listing other reasons for limited duty (e.g. post-traumatic stress disorder, pregnancy, back pain) in addition to lower limb injury, we identified and excluded multi-reason profiles and recalculated the proportions of limited duty time. Second, to examine the impact of the distinct high-utilization population of soldiers who required limited duty for almost all of their service time during the year, we excluded those soldiers with limited duty lasting 90% or more of their service time and recalculated the proportions of limited duty time. All analyses were conducted in 2017 using Stata MP, version 14. This research was approved by Stanford University’s Institutional Review Board and by the Defense Health Agency Human Research Protection Office. Results The population available for study was 581 800 US Army personnel with 6.2 million person-months of service. Eighty-five soldiers with inconsistently recorded gender were excluded. After applying restrictions, there were 568 753 soldiers (14% female) with 5.7 million months of service during calendar year 2014 in the final study population. Population demographics are summarized in Table 1. We identified a total of 317 666 profiles for lower limb injuries (Table 2). Common activity restrictions entailed by the profiles were physical training activities including running (54% of profiles), ruck marching (51%), and jumping (37%), and military functional activities such as moving a 40-pound load (50%), wearing body armour (45%), and wearing load bearing equipment (45%). Complete results of the specified restricted activities are shown in Supplementary Table 2 (available at Occupational Medicine Online). Table 1. Demographic and occupational characteristics of the study population   Women (N = 78 650), n (%)  Men (N = 490 103), n (%)  Total (N = 568 753), n (%)  Age (years)   ≤20  10 456 (13)  61 227 (12)  71 683 (13)   21–30  41 634 (53)  254 002 (52)  295 636 (52)   31–40  19 457 (25)  128 279 (26)  147 736 (26)   ≥41  7103 (9)  46 595 (10)  53 698 (9)  Year of service entry   Pre-2011  46 327 (59)  305 899 (62)  352 226 (62)   2011  7297 (9)  42 238 (9)  49 535 (9)   2012  7714 (10)  46 442 (9)  54 156 (9)   2013–14  17 312 (22)  95 524 (20)  112 836 (20)  Pay grade/Military occupationa   Officer  17 092 (22)  85 652 (17)  102 744 (18)   Enlisted:    Infantry/SF/Armour (11,18,19)  –  104 868 (21)  104 868 (18)    Ordnance (89,91,94)  4880 (6)  47 406 (10)  52 286 (9)    Supply (92)  14 871 (19)  35 498 (7)  50 369 (9)    Medical (68)  10 610 (13)  29 821 (6)  40 431 (7)    Signal Corps (25)  5116 (6)  30 935 (6)  36 051 (6)    Intel/Combat Support (09,35,74)  6651 (8)  27 796 (6)  34 447 (6)    Artillery (13,14)  1232 (2)  32 313 (7)  33 545 (6)    Aviation (15)  1972 (3)  23 909 (5)  25 881 (5)    Engineer (12)  9641 (1)  19 781 (4)  20 745 (4)    Admin/Finance/Legal (27,36,42,56)  7625 (10)  13 058 (3)  20 683 (4)    Transportation (88)  3663 (5)  16 322 (3)  19 985 (4)    Military Police (31)  2899 (4)  15 449 (3)  18 348 (3)    Other/Unknown  1075 (1)  7295 (2)  8370 (1)    Women (N = 78 650), n (%)  Men (N = 490 103), n (%)  Total (N = 568 753), n (%)  Age (years)   ≤20  10 456 (13)  61 227 (12)  71 683 (13)   21–30  41 634 (53)  254 002 (52)  295 636 (52)   31–40  19 457 (25)  128 279 (26)  147 736 (26)   ≥41  7103 (9)  46 595 (10)  53 698 (9)  Year of service entry   Pre-2011  46 327 (59)  305 899 (62)  352 226 (62)   2011  7297 (9)  42 238 (9)  49 535 (9)   2012  7714 (10)  46 442 (9)  54 156 (9)   2013–14  17 312 (22)  95 524 (20)  112 836 (20)  Pay grade/Military occupationa   Officer  17 092 (22)  85 652 (17)  102 744 (18)   Enlisted:    Infantry/SF/Armour (11,18,19)  –  104 868 (21)  104 868 (18)    Ordnance (89,91,94)  4880 (6)  47 406 (10)  52 286 (9)    Supply (92)  14 871 (19)  35 498 (7)  50 369 (9)    Medical (68)  10 610 (13)  29 821 (6)  40 431 (7)    Signal Corps (25)  5116 (6)  30 935 (6)  36 051 (6)    Intel/Combat Support (09,35,74)  6651 (8)  27 796 (6)  34 447 (6)    Artillery (13,14)  1232 (2)  32 313 (7)  33 545 (6)    Aviation (15)  1972 (3)  23 909 (5)  25 881 (5)    Engineer (12)  9641 (1)  19 781 (4)  20 745 (4)    Admin/Finance/Legal (27,36,42,56)  7625 (10)  13 058 (3)  20 683 (4)    Transportation (88)  3663 (5)  16 322 (3)  19 985 (4)    Military Police (31)  2899 (4)  15 449 (3)  18 348 (3)    Other/Unknown  1075 (1)  7295 (2)  8370 (1)  Numbers include all soldiers in the study population weighted equally with no adjustment for differences in service time during 2014. aDigits in parentheses denote the first two digits of the military occupational speciality codes corresponding to the named occupation. View Large Table 2. Profiles related to lower limb musculoskeletal injuries or related conditions by soldier gender during 2014   Women  Men  Total  Number of profiles  64 249  253 417  317 666    n (%)  n (%)  n (%)  Body region   Hip/thigh  14 133 (22)  21 445 (8)  35 578 (11)   Knee  19 703 (31)  106 476 (42)  126 179 (40)   Lower leg/ankle  10 415 (16)  55 682 (22)  66 097 (21)   Foot  9969 (16)  33 233 (13)  43 202 (13)   Multiple  5244 (8)  16 715 (7)  21 959 (7)   Unspecified  4785 (7)  19 866 (8)  24 651 (8)  Lower extremity limitation score   2  30 440 (47)  120 799 (48)  151 239 (48)   3  33 780 (53)  132 505 (52)  166 285 (52)   4  29 (0)  113 (0)  142 (0)  Permanent  17 093 (27)  62 389 (25)  79 482 (25)  Temporary  47 156 (73)  191 028 (75)  238 184 (75)    Women  Men  Total  Number of profiles  64 249  253 417  317 666    n (%)  n (%)  n (%)  Body region   Hip/thigh  14 133 (22)  21 445 (8)  35 578 (11)   Knee  19 703 (31)  106 476 (42)  126 179 (40)   Lower leg/ankle  10 415 (16)  55 682 (22)  66 097 (21)   Foot  9969 (16)  33 233 (13)  43 202 (13)   Multiple  5244 (8)  16 715 (7)  21 959 (7)   Unspecified  4785 (7)  19 866 (8)  24 651 (8)  Lower extremity limitation score   2  30 440 (47)  120 799 (48)  151 239 (48)   3  33 780 (53)  132 505 (52)  166 285 (52)   4  29 (0)  113 (0)  142 (0)  Permanent  17 093 (27)  62 389 (25)  79 482 (25)  Temporary  47 156 (73)  191 028 (75)  238 184 (75)  View Large Twenty-four per cent of men (n = 117 076) and 35% of women (n = 27 360) were assigned one or more profiles for lower limb injuries. The distribution of individual limited duty time for those soldiers is shown in Figure 1. Altogether, lower limb limited duty affected 13% of service days in 2014, including 11% and 19% of days for male and female soldiers, respectively (Figure 2). Permanent profiles accounted for 67% of those limited duty days. Figure 1. View largeDownload slide Distribution of individual percentages of service days with limited duty for lower limb musculoskeletal injuries or related conditions in 2014 by gender. Only soldiers with non-zero time of limited duty are shown so the sum of the bar heights is 24% for men and 35% for women. The median proportions of limited duty time apply to only soldiers with non-zero limited-duty days. Figure 1. View largeDownload slide Distribution of individual percentages of service days with limited duty for lower limb musculoskeletal injuries or related conditions in 2014 by gender. Only soldiers with non-zero time of limited duty are shown so the sum of the bar heights is 24% for men and 35% for women. The median proportions of limited duty time apply to only soldiers with non-zero limited-duty days. Figure 2. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by gender and profile type. The labels indicate cumulative percent of service days with limited duty. Figure 2. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by gender and profile type. The labels indicate cumulative percent of service days with limited duty. Forty-five per cent of the lower limb limited duty days were attributable to the knee (6% of service days overall), followed by lower leg/ankle (2% of service days overall), foot (2%), multiple lower limb regions (1%), hip/thigh (1%) and unspecified lower limb regions (<1%) (Figure 3). For each body region, women required more limited-duty days than men. In particular, for hip and thigh injuries, women required four times more limited-duty time than men. Figure 3. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by affected body region and gender. Figure 3. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by affected body region and gender. Stratified estimates of limited duty rates by gender and military occupation are shown in Figure 4. Within each gender-integrated occupation, female soldiers experienced higher proportions of limited-duty time than their male counterparts. The relative increases ranged from 27% (in the military police) to 57% in the medical occupation. For men, the proportion of service time with limited duty ranged from 7% for infantry/special forces/armour occupations to 17% for soldiers in transportation. For women, this proportion ranged from 13% of days for officers to 23% for soldiers in administrative/finance/legal occupations. Figure 4. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by rank, military occupational specialty, and gender. Officers were combined into a single category, while enlisted personnel were organized by military occupation. Infantry, Special Forces (SF) and Armour occupations were male-only during the period of this study (2014). Figure 4. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by rank, military occupational specialty, and gender. Officers were combined into a single category, while enlisted personnel were organized by military occupation. Infantry, Special Forces (SF) and Armour occupations were male-only during the period of this study (2014). The first sensitivity analysis revealed that 19% of profiles for lower limb injury also listed additional medical reason(s) for limited duty. After exclusion of these multi-reason profiles, the remaining subset of profiles accounted for limited duty on 10% of service days. Within this limited set of profiles, within occupations, female soldiers experienced 35–70% greater proportions of limited duty time compared with men. The second sensitivity analysis showed that 7% of men (n = 33 718) and 12% of women (n = 9631) required limited duty 90% or more of their service days during 2014 (Figure 1). After excluding these soldiers, the remaining 92% of soldiers required limited duty during just 5% of overall service time. Within occupations, female soldiers experienced 39–72% greater proportions of limited duty time compared with men after excluding this very high utilizing group. Discussion This study found that in 2014, 13% of service days for active-duty US Army soldiers involved duty limitations for lower limb musculoskeletal injuries or related conditions (hereafter called injuries). Knee injuries were responsible for the largest number of limited duty days (6% of service days overall). Within integrated occupational specialities, female soldiers experienced 27–57% more limited duty time than men. The primary strength of this analysis is the novel use of the electronic profile data to measure specific individual duty limitations for the full population of active-duty soldiers. These data represent the gold standard record of soldier medical status and provide new detail on the nature and duration of limitations. Furthermore, this study is the first to compare rates of lower limb limited duty between men and women serving on regular duty. This study had two main limitations. First, with the month-level dataset, we could not identify the exact dates of service entry and exit, or of profile assignment and expiration. Our imputed dates resulted in a slight overestimate of follow-up time and a more conservative estimate of the proportion of limited duty days. Second, we found that 19% of the lower limb injury profiles specified more than one medical reason for limited duty. We included all lower limb injury profiles regardless of mention of other medical reasons, which may have resulted in an overestimate of limited duty time. Still, in a sensitivity analysis excluding multi-reason profiles, an estimated 10% of days involved duty limitations due to lower limb injuries. The current findings of gender differences in lower limb limited duty align with previous studies of injury incidence during BCT, which showed lower limb and time-loss injury rates for women between 1.5 and 2.2 times those of men [5–7,17]. Further, Bijur et al. found that women spent 50% more days excused from regular activities for each injury episode compared with men [6]. One advantage of studying BCT is the relatively uniform training for men and women. However, the highly specific time frame and sample limit generalizability to all service members on regular duty. The current results reveal persistent gender differences in lower limb-related limitations beyond BCT among the total active-duty population. This study’s overall estimates of lower limb limited duty suggest a substantially greater impact of lower limb limited duty compared to prior work by Ruscio et al. [2]. Based on diagnosis codes and associated average recovery times, they estimated a total of 25 million injury-related limited duty days (approximately 6% of service days) for the active-duty Department of Defense in 2004. If the lower limb accounted for half of these days, then 3% of service days required lower limb limited duty, compared to the 13% found in the current study. An important methodological difference was that the estimate of Ruscio et al. included only limited-duty days directly associated with incident diagnoses. The current estimate includes limited-duty days due to both incident injuries and chronic effects of earlier injuries (identified by permanent profiles initiated prior to the study window). The use of electronic profile data in this study should yield a more accurate measure of soldiers’ limited duty experience compared with estimates using average recovery time. At the same time, the US Army’s higher-than-average injury rates within the Department of Defense [1,3] or secular increases in utilization between 2004 and 2014 may have contributed to our higher estimate. A central finding of this study was that for female soldiers, 19% of service days involved duty limitations for lower limb injuries. Within military occupations, women experienced 27–57% more time with lower limb limited duty compared with men. Physiological, musculoskeletal, and/or biomechanical differences between men and women may contribute to female soldiers’ increased risk of lower limb injuries and associated limited duty. On average, women have shorter height, less muscle mass and greater percent body fat [5,18,19]. Women on average also have lower aerobic fitness, a consistent risk factor for training injuries, and display lower muscular strength per unit of body mass [5,7,18–21]. Biomechanical differences, including greater knee valgus angle on jump landings, may also add to female soldiers’ injury risk [18,19,22]. Notably, hip and thigh injuries required more than four times the limited-duty days for women compared with men. This difference is consistent with dramatic gender differences in hip injury rates among service members reported elsewhere [23]. Shorter female height may necessitate over-striding while marching in formation, which could cause hip problems [24]. Given these differences, gender-specific interventions to improve fitness and biomechanical adaptation to the physical demands of the military may help to decrease injury risk and optimize readiness [25,26]. A second key finding of this study was the high rate of limited duty caused by knee injuries, which far outweighed those of other body regions. Prior epidemiological studies among soldiers have pinpointed the knee as the site of 10 to 34% of musculoskeletal training injuries and a common site for re-injury [27,28]. Simple screening tests may help to identify subgroups at greater risk for knee pain upon service entry [29]. The impact of knee injuries on occupational functions and military readiness should place them as a priority for screening, prevention and timely treatment efforts among all soldiers. Across diverse military occupations, the percent of person-time with duty limitations varied widely, from 7 to 17% for men and from 13 to 23% for women. Interestingly, however, within each integrated occupation, women consistently required more duty-limited days then did men, with relative increases ranging from 27% (in the military police) to 57% in the medical occupation. These findings suggest that occupational differences in culture and job requirements may influence male and female soldiers’ time spent with lower limb limited duty, but that there is a relatively consistent effect of female gender across occupations. It is important to emphasize that the aggregated estimate that 13% of service days required lower limb limited duty does not represent the experience of the typical active-duty soldier. Seventy-five per cent of soldiers studied did not receive a lower limb profile, while 8% of soldiers required limited duty for at least 90% of their observed service time. This sizable high-utilization population dramatically influenced the overall proportion of limited-duty time. Still, even when excluding that large subset, the excess impact of lower limb injury among women in the aggregate was clear and consistent. Looking ahead, these findings signal the importance of continual surveillance of injuries and associated limited duty with the expansion of women’s roles in the US Army. As of 2 January 2016, an additional 220 000 previously male-only positions were opened to female soldiers [15,30]. It remains to be seen how injury rates and duty limitations will differ between men and women working in previously male-only specialities, such as infantry and special operations forces. The results of this study provide foundational pre-integration rates of lower-limb-related limited duty, and ongoing longitudinal assessment will allow continual analysis to provide training and administrative guidance for integrated military occupations. Key points An analysis of individual limited duty assignments (profiles) showed that 13% of service days for active-duty US Army soldiers (n = 568 753, 14% women) required limited duty for lower limb musculoskeletal injuries and related conditions in 2014. Injuries to the knee were responsible for 45% of these limited duty days. Within integrated military occupations, female soldiers experienced 27–57% more time on limited duty for lower limb musculoskeletal injuries and related conditions compared with men. Funding This study was supported by a grant from the US Army Medical Department Advanced Medical Technology Initiative, which had no role in study design; collection, analysis, or interpretation of data; writing the report; or the decision to submit the report for publication. Financial disclosure: No financial disclosures were reported by the authors of this article. Disclaimer: The views expressed in this article are those of the authors and do not reflect the views or official policies of the US Government, the Department of Defense, the Defense Health Agency, the Department of the Army, or the US Army Medical Command. Conflicts of interest None declared. Acknowledgements The authors would like to thank the thousands of US Army soldiers in the study population for their service to this country. This study was supported by an award from the FY 15 Army Medical Department Advanced Medical Technology Initiative. All data used in the study were provided under a cooperative agreement with the US Army Medical Command. References 1. Jones BH, Canham-Chervak M, Canada S, Mitchener TA, Moore S. Medical surveillance of injuries in the U.S. Military. Am J Prev Med  2010; 38( 1 Suppl): S42– 60. Google Scholar CrossRef Search ADS PubMed  2. Ruscio BA, Jones BH, Bullock SHet al.   A process to identify military injury prevention priorities based on injury type and limited duty days. Am J Prev Med  2010; 38: S19– S33. Google Scholar CrossRef Search ADS PubMed  3. Hauret KG, Bedno S, Loringer K, Kao TC, Mallon T, Jones BH. Epidemiology of exercise- and sports-related injuries in a population of young, physically active adults: a survey of military service members. Am J Sports Med  2015; 43: 2645– 2653. Google Scholar CrossRef Search ADS PubMed  4. Roy TC, Knapik JJ, Ritland BM, Murphy N, Sharp MA. Risk factors for musculoskeletal injuries for soldiers deployed to Afghanistan. Aviat Space Environ Med  2012; 83: 1060– 1066. Google Scholar CrossRef Search ADS PubMed  5. Bell NS, Mangione TW, Hemenway D, Amoroso PJ, Jones BH. High injury rates among female army trainees: a function of gender? Am J Prev Med  2000; 18: 141– 146. Google Scholar CrossRef Search ADS PubMed  6. Bijur PE, Horodyski M, Egerton W, Kurzon M, Lifrak S, Friedman S. Comparison of injury during cadet basic training by gender. Arch Pediatr Adolesc Med  1997; 151: 456– 461. Google Scholar CrossRef Search ADS PubMed  7. Knapik JJ, Sharp MA, Canham-Chervak M, Hauret K, Patton JF, Jones BH. Risk factors for training-related injuries among men and women in basic combat training. Med Sci Sports Exerc  2001; 33: 946– 954. Google Scholar CrossRef Search ADS PubMed  8. Altarac M, Gardner JW, Popovich RM, Potter R, Knapik JJ, Jones BH. Cigarette smoking and exercise-related injuries among young men and women. Am J Prev Med  2000; 18: 96– 102. Google Scholar CrossRef Search ADS PubMed  9. Knapik JJ, Graham B, Cobbs J, Thompson D, Steelman R, Jones BH. A prospective investigation of injury incidence and injury risk factors among Army recruits in military police training. BMC Musculoskelet Disord  2013; 14: 32. Google Scholar CrossRef Search ADS PubMed  10. Wentz L, Liu PY, Haymes E, Ilich JZ. Females have a greater incidence of stress fractures than males in both military and athletic populations: a systemic review. Mil Med  2011; 176: 420– 430. Google Scholar CrossRef Search ADS PubMed  11. Yates B, White S. The incidence and risk factors in the development of medial tibial stress syndrome among naval recruits. Am J Sports Med  2004; 32: 772– 780. Google Scholar CrossRef Search ADS PubMed  12. Boling M, Padua D, Marshall S, Guskiewicz K, Pyne S, Beutler A. Gender differences in the incidence and prevalence of patellofemoral pain syndrome. Scand J Med Sci Sports  2010; 20: 725– 730. Google Scholar CrossRef Search ADS PubMed  13. Reynolds K, Cosio-Lima L, Bovill M, Tharion W, Williams J, Hodges T. A comparison of injuries, limited-duty days, and injury risk factors in infantry, artillery, construction engineers, and special forces soldiers. Mil Med  2009; 174: 702– 708. Google Scholar CrossRef Search ADS PubMed  14. Feuerstein M, Berkowitz SM, Peck CAJr. Musculoskeletal-related disability in US Army personnel: prevalence, gender, and military occupational specialties. J Occup Environ Med  1997; 39: 68– 78. Google Scholar CrossRef Search ADS PubMed  15. U.S. Secretary of Defense. Implementation Guidance for the Full Integration of Women in the Armed Forces [Internet] . Washington, DC: U.S. Department of Defense, 2015. http://www.defense.gov/Portals/1/Documents/pubs/OSD014303-15.pdf (2 August 2017, date last accessed). 16. U.S. Department of the Army. Standards of Medical Fitness, Army Regulation 40–501. [Internet]. 2011. http://www.au.af.mil/au/awc/awcgate/army/r40_501.pdf (2 August 2017, date last accessed). 17. Jones BH, Bovee MW, Harris JMIII, Cowan DN. Intrinsic risk factors for exercise-related injuries among male and female army trainees. Am J Sports Med  1993; 21: 705– 710. Google Scholar CrossRef Search ADS PubMed  18. Allison KF, Keenan KA, Sell TC, Abt JP, McGrail M. Musculoskeletal, biomechanical, and physiological gender differences in the US military. Army Med Dep J  2015: 22– 32. 19. Beutler A, de la Motte S, Marshall S, Padua D, Boden B. Muscle strength and qualitative jump-landing differences in male and female military cadets: the jump-acl study. J Sports Sci Med  2009; 8: 663– 671. Google Scholar PubMed  20. Cowan DN, Bedno SA, Urban N, Lee DS, Niebuhr DW. Step test performance and risk of stress fractures among female army trainees. Am J Prev Med  2012; 42: 620– 624. Google Scholar CrossRef Search ADS PubMed  21. Gilchrist J, Jones BH, Sleet DA, Kimsey CD; CDC. Exercise-related injuries among women: strategies for prevention from civilian and military studies. MMWR Recomm Rep  2000; 49: 15– 33. Google Scholar PubMed  22. Hewett TE, Myer GD, Ford KRet al.   Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: a prospective study. Am J Sports Med  2005; 33: 492– 501. Google Scholar CrossRef Search ADS PubMed  23. Loringer K, Bedno S, Hauret K, Jones B, Kao T, Mallon T. Injuries from Participation in Sports, Exercise, and Recreational Activities Among Active Duty Service Members — Analysis of the April 2008 Status of Forces Survey of Active Duty Members [Internet] . Aberdeen, MD: U.S. Army Public Health Command; 2011. http://www.dtic.mil/dtic/tr/fulltext/u2/a560733.pdf (2 August 2017, date last accessed). 24. Kelly EW, Jonson SR, Cohen ME, Shaffer R. Stress fractures of the pelvis in female navy recruits: an analysis of possible mechanisms of injury. Mil Med  2000; 165: 142– 146. Google Scholar PubMed  25. Knapik JJ, Bullock SH, Canada Set al.   Influence of an injury reduction program on injury and fitness outcomes among soldiers. Inj Prev  2004; 10: 37– 42. Google Scholar CrossRef Search ADS PubMed  26. Hewett TE, Myer GD, Ford KR. Reducing knee and anterior cruciate ligament injuries among female athletes: a systematic review of neuromuscular training interventions. J Knee Surg  2005; 18: 82– 88. Google Scholar CrossRef Search ADS PubMed  27. Hill OT, Kay AB, Wahi MM, McKinnon CJ, Bulathsinhala L, Haley TF. Rates of knee injury in the U.S. Active Duty Army, 2000–2005. Mil Med  2012; 177: 840– 844. Google Scholar CrossRef Search ADS PubMed  28. Kaufman KR, Brodine S, Shaffer R. Military training-related injuries: surveillance, research, and prevention. Am J Prev Med  2000; 18: 54– 63. Google Scholar CrossRef Search ADS PubMed  29. Larsson H, Larsson M, Osterberg H, Harms-Ringdahl K. Screening tests detect knee pain and predict discharge from military service. Mil Med  2008; 173: 259– 265. Google Scholar CrossRef Search ADS PubMed  30. Army Public Affairs. Army Outlines Gender Integration Implementation Plan [Internet] . Washington, DC: U.S. Army; 2016. https://www.army.mil/article/163980/army_outlines_gender_integration_implementation_plan (2 August 2017, date last accessed). Published by Oxford University Press on behalf of The Society of Occupational Medicine 2017. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Occupational Medicine Oxford University Press

Gender differences in limited duty time for lower limb injury

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Oxford University Press
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Published by Oxford University Press on behalf of The Society of Occupational Medicine 2017.
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0962-7480
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1471-8405
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10.1093/occmed/kqx169
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Abstract

Abstract Background Among active-duty military personnel, lower limb musculoskeletal injuries and related conditions (injuries) frequently arise as unintended consequences of physical training. These injuries are particularly common among women. The practical impact of such injuries on temporary military occupational disability has not been estimated with precision on a large scale. Aims To determine the proportion of service time compromised by limited duty days attributable to lower limb injuries, characterize the time affected by these limitations in terms of specific lower limb region and compare the limited duty time between male and female soldiers. Methods Administrative data and individual limited duty assignments (profiles) were obtained for active-duty US Army personnel who served in 2014. Lower limb injury-related profiles were used to calculate the percent of person-time requiring duty limitations by gender and body region. Results The study group was 568 753 soldiers of whom 14% were women. Nearly 13% of service days for active-duty US Army soldiers required limited duty for lower limb injuries during 2014. Knee injuries were responsible for 45% of those days. Within integrated military occupations, female soldiers experienced 27–57% more time on limited duty for lower limb injuries compared with men. Conclusions The substantial amount of limited duty for lower limb musculoskeletal injuries among soldiers highlights the need for improvement in training-related injury screening, prevention and timely treatment with particular attention to knee injuries. The excessive impact of lower limb injuries on female soldiers’ occupational functions should be a surveillance priority in the current environment of expanding gender-integrated training. Injury, military, musculoskeletal, women Introduction For active-duty US Army soldiers, regular physical training is a critical daily job function. Common unintended consequences of this training include lower limb musculoskeletal injuries and injury-related conditions. Within an otherwise healthy and carefully-screened young adult population, injuries of all types required over 750 000 medical visits for the approximately 360 000 person-years of non-deployed service time for the active-duty US Army in 2006 [1]. Half of these visits were attributable to lower limb overuse injuries such as stress fractures, Achilles tendonitis and plantar fasciitis [1]. Prior cross-sectional studies have estimated that lower limb injuries and related conditions require millions of days per year of limited duty for the active-duty US military [2,3]. The proportion of service time requiring injury-related limited duty provides a practical metric of the impact of injuries on job function, with implications for losses in unit productivity and deployment readiness. Accurate measures of limited duty are necessary in planning for military operations, evaluating training regimens from a risk-benefit perspective, and prioritizing prevention efforts. Because limited-duty days are not systematically recorded in the outpatient record, past studies have relied upon average civilian recovery times and retrospective surveys of service members to approximate days of limited duty [2–4]. There have been no large studies of limited duty associated with lower limb musculoskeletal injury as defined by ‘profiles.’ US Army clinicians use profiles to (i) record the nature, severity, duration and medical reasons for a soldier’s inability to fulfil his or her occupational requirements and (ii) to communicate these limitations to the soldier’s commander. Profiles may be assigned as temporary to cover short-term recovery periods for injuries or illnesses, or permanent to reflect conditions requiring chronic duty limitations. Studying profiles is essential when defining limited duty because these formal assignments represent the gold standard for a soldier’s functional status in US Army medical records. The electronic system for recording profiles, eProfile, constitutes a rich dataset that can be used to assess the annual proportion of service time compromised by limited duty. These data provide detail on the medical reasons for limited duty and the degree and duration of limitation. Prior studies have also not compared rates of limited duty for lower limb injuries between men and women. Female soldiers and trainees appear more susceptible to injuries than males, both in general [4–9] and for a broad range of specific lower limb injuries including stress fractures [6,10], medial tibial stress syndrome [11] and patellofemoral pain syndrome [12]. Therefore, it is likely that lower limb injuries and related conditions require more duty limitations for women than for men. Further, variability among different military occupations with respect to job responsibilities, physical training and culture may differentially affect the injury and limited duty rates for men and women [13,14]. The importance of assessing any gender-based risk difference is only increasing as all positions in the US armed forces are now open to women [15]. We therefore analysed temporary and permanent profiles for all soldiers serving on active duty in the US Army during calendar year 2014 to: (i) determine the proportion of service time compromised by limited duty days attributable to lower limb musculoskeletal injuries and related conditions, (ii) characterize the time affected by these limitations in terms of specific lower limb region and (iii) compare the proportion of limited duty experienced by men and women. Methods For this cross-sectional study, we utilized data from the Stanford Military Data Repository, a longitudinal dataset organized at the person-month level on the active-duty US Army population. Available data included demographic characteristics, military occupation, time spent in service and profiles containing duty restrictions assigned by clinicians to individual soldiers. All soldiers serving on active duty at any point in 2014 were initially deemed eligible for inclusion. However, because exploratory data analysis revealed that digital profiles in the eProfile system were seldom used to record limited duty days during basic combat training (BCT), the first 3 months of service for new soldiers were not included in this analysis. Additionally, the person-months spent on combat deployment (6% of the total available) and the profile assignments made during those months were excluded from this analysis, because duty limitations during combat may occur due to different problems than during training and may be addressed and documented differently. Finally, we excluded soldiers with inconsistently recorded gender, which likely reflected data entry errors because openly transgender persons were not permitted to serve in the US Army in 2014. The primary predictor of interest was gender. Other covariates were age (≤20, 21–30, 31–40 or >40), year of service entry (pre-2011, 2011, 2012 or 2013–14), pay grade (officer or enlisted) and broad category of military occupation for enlisted personnel. The primary outcome for this analysis was the proportion of service days during calendar year 2014 with limited duty indicated by any temporary or permanent profile attributable to a lower limb musculoskeletal injury or related condition (injury). Lower limb regions included were the hip, thigh, knee, lower leg, ankle and foot. The lower back was not included. Our injury definition included inflammation and pain, tendonitis, fasciitis, joint derangement, dislocation, stress injury/fracture, sprain, strain, and rupture, and excluded contusions, crushes, wounds, and infections. According to the US Army profile system, temporary profiles are designated for a specific number of days, while permanent profiles are assigned with no expiration date and are re-evaluated at annual periodic health assessments [16]. Each profile includes a numeric score for each of six body regions, one of which is lower extremity. A score of 1 indicates full capacity, and scores of 2, 3 or 4 indicate progressively greater functional limitations. Each profile also includes a medical condition text field where the clinician records the reason(s) for limited duty using common terminology. For this analysis, we included those profiles with a lower extremity limitation score of 2, 3 or 4 that also denoted lower limb injury in the medical condition text field, based on key terms derived from our injury definition (the key terms are listed in Supplementary Section 1, available at Occupational Medicine Online). Profiles listing multiple medical reasons were included if any of the reasons was lower limb injury. We classified these profiles into six mutually exclusive body region categories: hip/thigh, knee, lower leg/ankle, foot, multiple lower limb regions and unspecified lower limb. The full classification algorithms and accuracy assessments are described in Supplementary Section 1 (available at Occupational Medicine Online) and sample medical conditions classified within each body region are shown in Supplementary Table 1 (available at Occupational Medicine Online). The classification algorithm used to identify profiles attributable to lower limb injury demonstrated strong accuracy in comparison to clinician assessment of profile reason from the medical condition, with a sensitivity of 98%, specificity of 93%, negative predictive value of 95% and positive predictive value of 96%. This set of profiles was used to calculate the number of limited-duty days and proportion of service time on limited duty for each soldier for each body region (details are in Supplementary Section 2, available at Occupational Medicine Online). These proportions were aggregated by gender and for the full population by summing the total number of limited-duty days and dividing by the total number of service days. Secondary analyses stratified these calculations by pay grade and military occupation to examine potential confounding. To illustrate the main types of activity restrictions entailed by the profiles, we summarized the proscribed activities noted in pre-specified fields and in the text field for clinician comments. Details on this descriptive analysis are given in Supplementary Section 3 (available at Occupational Medicine Online). We conducted two sensitivity analyses. First, to examine the impact of including profiles listing other reasons for limited duty (e.g. post-traumatic stress disorder, pregnancy, back pain) in addition to lower limb injury, we identified and excluded multi-reason profiles and recalculated the proportions of limited duty time. Second, to examine the impact of the distinct high-utilization population of soldiers who required limited duty for almost all of their service time during the year, we excluded those soldiers with limited duty lasting 90% or more of their service time and recalculated the proportions of limited duty time. All analyses were conducted in 2017 using Stata MP, version 14. This research was approved by Stanford University’s Institutional Review Board and by the Defense Health Agency Human Research Protection Office. Results The population available for study was 581 800 US Army personnel with 6.2 million person-months of service. Eighty-five soldiers with inconsistently recorded gender were excluded. After applying restrictions, there were 568 753 soldiers (14% female) with 5.7 million months of service during calendar year 2014 in the final study population. Population demographics are summarized in Table 1. We identified a total of 317 666 profiles for lower limb injuries (Table 2). Common activity restrictions entailed by the profiles were physical training activities including running (54% of profiles), ruck marching (51%), and jumping (37%), and military functional activities such as moving a 40-pound load (50%), wearing body armour (45%), and wearing load bearing equipment (45%). Complete results of the specified restricted activities are shown in Supplementary Table 2 (available at Occupational Medicine Online). Table 1. Demographic and occupational characteristics of the study population   Women (N = 78 650), n (%)  Men (N = 490 103), n (%)  Total (N = 568 753), n (%)  Age (years)   ≤20  10 456 (13)  61 227 (12)  71 683 (13)   21–30  41 634 (53)  254 002 (52)  295 636 (52)   31–40  19 457 (25)  128 279 (26)  147 736 (26)   ≥41  7103 (9)  46 595 (10)  53 698 (9)  Year of service entry   Pre-2011  46 327 (59)  305 899 (62)  352 226 (62)   2011  7297 (9)  42 238 (9)  49 535 (9)   2012  7714 (10)  46 442 (9)  54 156 (9)   2013–14  17 312 (22)  95 524 (20)  112 836 (20)  Pay grade/Military occupationa   Officer  17 092 (22)  85 652 (17)  102 744 (18)   Enlisted:    Infantry/SF/Armour (11,18,19)  –  104 868 (21)  104 868 (18)    Ordnance (89,91,94)  4880 (6)  47 406 (10)  52 286 (9)    Supply (92)  14 871 (19)  35 498 (7)  50 369 (9)    Medical (68)  10 610 (13)  29 821 (6)  40 431 (7)    Signal Corps (25)  5116 (6)  30 935 (6)  36 051 (6)    Intel/Combat Support (09,35,74)  6651 (8)  27 796 (6)  34 447 (6)    Artillery (13,14)  1232 (2)  32 313 (7)  33 545 (6)    Aviation (15)  1972 (3)  23 909 (5)  25 881 (5)    Engineer (12)  9641 (1)  19 781 (4)  20 745 (4)    Admin/Finance/Legal (27,36,42,56)  7625 (10)  13 058 (3)  20 683 (4)    Transportation (88)  3663 (5)  16 322 (3)  19 985 (4)    Military Police (31)  2899 (4)  15 449 (3)  18 348 (3)    Other/Unknown  1075 (1)  7295 (2)  8370 (1)    Women (N = 78 650), n (%)  Men (N = 490 103), n (%)  Total (N = 568 753), n (%)  Age (years)   ≤20  10 456 (13)  61 227 (12)  71 683 (13)   21–30  41 634 (53)  254 002 (52)  295 636 (52)   31–40  19 457 (25)  128 279 (26)  147 736 (26)   ≥41  7103 (9)  46 595 (10)  53 698 (9)  Year of service entry   Pre-2011  46 327 (59)  305 899 (62)  352 226 (62)   2011  7297 (9)  42 238 (9)  49 535 (9)   2012  7714 (10)  46 442 (9)  54 156 (9)   2013–14  17 312 (22)  95 524 (20)  112 836 (20)  Pay grade/Military occupationa   Officer  17 092 (22)  85 652 (17)  102 744 (18)   Enlisted:    Infantry/SF/Armour (11,18,19)  –  104 868 (21)  104 868 (18)    Ordnance (89,91,94)  4880 (6)  47 406 (10)  52 286 (9)    Supply (92)  14 871 (19)  35 498 (7)  50 369 (9)    Medical (68)  10 610 (13)  29 821 (6)  40 431 (7)    Signal Corps (25)  5116 (6)  30 935 (6)  36 051 (6)    Intel/Combat Support (09,35,74)  6651 (8)  27 796 (6)  34 447 (6)    Artillery (13,14)  1232 (2)  32 313 (7)  33 545 (6)    Aviation (15)  1972 (3)  23 909 (5)  25 881 (5)    Engineer (12)  9641 (1)  19 781 (4)  20 745 (4)    Admin/Finance/Legal (27,36,42,56)  7625 (10)  13 058 (3)  20 683 (4)    Transportation (88)  3663 (5)  16 322 (3)  19 985 (4)    Military Police (31)  2899 (4)  15 449 (3)  18 348 (3)    Other/Unknown  1075 (1)  7295 (2)  8370 (1)  Numbers include all soldiers in the study population weighted equally with no adjustment for differences in service time during 2014. aDigits in parentheses denote the first two digits of the military occupational speciality codes corresponding to the named occupation. View Large Table 2. Profiles related to lower limb musculoskeletal injuries or related conditions by soldier gender during 2014   Women  Men  Total  Number of profiles  64 249  253 417  317 666    n (%)  n (%)  n (%)  Body region   Hip/thigh  14 133 (22)  21 445 (8)  35 578 (11)   Knee  19 703 (31)  106 476 (42)  126 179 (40)   Lower leg/ankle  10 415 (16)  55 682 (22)  66 097 (21)   Foot  9969 (16)  33 233 (13)  43 202 (13)   Multiple  5244 (8)  16 715 (7)  21 959 (7)   Unspecified  4785 (7)  19 866 (8)  24 651 (8)  Lower extremity limitation score   2  30 440 (47)  120 799 (48)  151 239 (48)   3  33 780 (53)  132 505 (52)  166 285 (52)   4  29 (0)  113 (0)  142 (0)  Permanent  17 093 (27)  62 389 (25)  79 482 (25)  Temporary  47 156 (73)  191 028 (75)  238 184 (75)    Women  Men  Total  Number of profiles  64 249  253 417  317 666    n (%)  n (%)  n (%)  Body region   Hip/thigh  14 133 (22)  21 445 (8)  35 578 (11)   Knee  19 703 (31)  106 476 (42)  126 179 (40)   Lower leg/ankle  10 415 (16)  55 682 (22)  66 097 (21)   Foot  9969 (16)  33 233 (13)  43 202 (13)   Multiple  5244 (8)  16 715 (7)  21 959 (7)   Unspecified  4785 (7)  19 866 (8)  24 651 (8)  Lower extremity limitation score   2  30 440 (47)  120 799 (48)  151 239 (48)   3  33 780 (53)  132 505 (52)  166 285 (52)   4  29 (0)  113 (0)  142 (0)  Permanent  17 093 (27)  62 389 (25)  79 482 (25)  Temporary  47 156 (73)  191 028 (75)  238 184 (75)  View Large Twenty-four per cent of men (n = 117 076) and 35% of women (n = 27 360) were assigned one or more profiles for lower limb injuries. The distribution of individual limited duty time for those soldiers is shown in Figure 1. Altogether, lower limb limited duty affected 13% of service days in 2014, including 11% and 19% of days for male and female soldiers, respectively (Figure 2). Permanent profiles accounted for 67% of those limited duty days. Figure 1. View largeDownload slide Distribution of individual percentages of service days with limited duty for lower limb musculoskeletal injuries or related conditions in 2014 by gender. Only soldiers with non-zero time of limited duty are shown so the sum of the bar heights is 24% for men and 35% for women. The median proportions of limited duty time apply to only soldiers with non-zero limited-duty days. Figure 1. View largeDownload slide Distribution of individual percentages of service days with limited duty for lower limb musculoskeletal injuries or related conditions in 2014 by gender. Only soldiers with non-zero time of limited duty are shown so the sum of the bar heights is 24% for men and 35% for women. The median proportions of limited duty time apply to only soldiers with non-zero limited-duty days. Figure 2. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by gender and profile type. The labels indicate cumulative percent of service days with limited duty. Figure 2. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by gender and profile type. The labels indicate cumulative percent of service days with limited duty. Forty-five per cent of the lower limb limited duty days were attributable to the knee (6% of service days overall), followed by lower leg/ankle (2% of service days overall), foot (2%), multiple lower limb regions (1%), hip/thigh (1%) and unspecified lower limb regions (<1%) (Figure 3). For each body region, women required more limited-duty days than men. In particular, for hip and thigh injuries, women required four times more limited-duty time than men. Figure 3. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by affected body region and gender. Figure 3. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by affected body region and gender. Stratified estimates of limited duty rates by gender and military occupation are shown in Figure 4. Within each gender-integrated occupation, female soldiers experienced higher proportions of limited-duty time than their male counterparts. The relative increases ranged from 27% (in the military police) to 57% in the medical occupation. For men, the proportion of service time with limited duty ranged from 7% for infantry/special forces/armour occupations to 17% for soldiers in transportation. For women, this proportion ranged from 13% of days for officers to 23% for soldiers in administrative/finance/legal occupations. Figure 4. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by rank, military occupational specialty, and gender. Officers were combined into a single category, while enlisted personnel were organized by military occupation. Infantry, Special Forces (SF) and Armour occupations were male-only during the period of this study (2014). Figure 4. View largeDownload slide Percent of service days in 2014 with limited duty for lower limb musculoskeletal injuries or related conditions by rank, military occupational specialty, and gender. Officers were combined into a single category, while enlisted personnel were organized by military occupation. Infantry, Special Forces (SF) and Armour occupations were male-only during the period of this study (2014). The first sensitivity analysis revealed that 19% of profiles for lower limb injury also listed additional medical reason(s) for limited duty. After exclusion of these multi-reason profiles, the remaining subset of profiles accounted for limited duty on 10% of service days. Within this limited set of profiles, within occupations, female soldiers experienced 35–70% greater proportions of limited duty time compared with men. The second sensitivity analysis showed that 7% of men (n = 33 718) and 12% of women (n = 9631) required limited duty 90% or more of their service days during 2014 (Figure 1). After excluding these soldiers, the remaining 92% of soldiers required limited duty during just 5% of overall service time. Within occupations, female soldiers experienced 39–72% greater proportions of limited duty time compared with men after excluding this very high utilizing group. Discussion This study found that in 2014, 13% of service days for active-duty US Army soldiers involved duty limitations for lower limb musculoskeletal injuries or related conditions (hereafter called injuries). Knee injuries were responsible for the largest number of limited duty days (6% of service days overall). Within integrated occupational specialities, female soldiers experienced 27–57% more limited duty time than men. The primary strength of this analysis is the novel use of the electronic profile data to measure specific individual duty limitations for the full population of active-duty soldiers. These data represent the gold standard record of soldier medical status and provide new detail on the nature and duration of limitations. Furthermore, this study is the first to compare rates of lower limb limited duty between men and women serving on regular duty. This study had two main limitations. First, with the month-level dataset, we could not identify the exact dates of service entry and exit, or of profile assignment and expiration. Our imputed dates resulted in a slight overestimate of follow-up time and a more conservative estimate of the proportion of limited duty days. Second, we found that 19% of the lower limb injury profiles specified more than one medical reason for limited duty. We included all lower limb injury profiles regardless of mention of other medical reasons, which may have resulted in an overestimate of limited duty time. Still, in a sensitivity analysis excluding multi-reason profiles, an estimated 10% of days involved duty limitations due to lower limb injuries. The current findings of gender differences in lower limb limited duty align with previous studies of injury incidence during BCT, which showed lower limb and time-loss injury rates for women between 1.5 and 2.2 times those of men [5–7,17]. Further, Bijur et al. found that women spent 50% more days excused from regular activities for each injury episode compared with men [6]. One advantage of studying BCT is the relatively uniform training for men and women. However, the highly specific time frame and sample limit generalizability to all service members on regular duty. The current results reveal persistent gender differences in lower limb-related limitations beyond BCT among the total active-duty population. This study’s overall estimates of lower limb limited duty suggest a substantially greater impact of lower limb limited duty compared to prior work by Ruscio et al. [2]. Based on diagnosis codes and associated average recovery times, they estimated a total of 25 million injury-related limited duty days (approximately 6% of service days) for the active-duty Department of Defense in 2004. If the lower limb accounted for half of these days, then 3% of service days required lower limb limited duty, compared to the 13% found in the current study. An important methodological difference was that the estimate of Ruscio et al. included only limited-duty days directly associated with incident diagnoses. The current estimate includes limited-duty days due to both incident injuries and chronic effects of earlier injuries (identified by permanent profiles initiated prior to the study window). The use of electronic profile data in this study should yield a more accurate measure of soldiers’ limited duty experience compared with estimates using average recovery time. At the same time, the US Army’s higher-than-average injury rates within the Department of Defense [1,3] or secular increases in utilization between 2004 and 2014 may have contributed to our higher estimate. A central finding of this study was that for female soldiers, 19% of service days involved duty limitations for lower limb injuries. Within military occupations, women experienced 27–57% more time with lower limb limited duty compared with men. Physiological, musculoskeletal, and/or biomechanical differences between men and women may contribute to female soldiers’ increased risk of lower limb injuries and associated limited duty. On average, women have shorter height, less muscle mass and greater percent body fat [5,18,19]. Women on average also have lower aerobic fitness, a consistent risk factor for training injuries, and display lower muscular strength per unit of body mass [5,7,18–21]. Biomechanical differences, including greater knee valgus angle on jump landings, may also add to female soldiers’ injury risk [18,19,22]. Notably, hip and thigh injuries required more than four times the limited-duty days for women compared with men. This difference is consistent with dramatic gender differences in hip injury rates among service members reported elsewhere [23]. Shorter female height may necessitate over-striding while marching in formation, which could cause hip problems [24]. Given these differences, gender-specific interventions to improve fitness and biomechanical adaptation to the physical demands of the military may help to decrease injury risk and optimize readiness [25,26]. A second key finding of this study was the high rate of limited duty caused by knee injuries, which far outweighed those of other body regions. Prior epidemiological studies among soldiers have pinpointed the knee as the site of 10 to 34% of musculoskeletal training injuries and a common site for re-injury [27,28]. Simple screening tests may help to identify subgroups at greater risk for knee pain upon service entry [29]. The impact of knee injuries on occupational functions and military readiness should place them as a priority for screening, prevention and timely treatment efforts among all soldiers. Across diverse military occupations, the percent of person-time with duty limitations varied widely, from 7 to 17% for men and from 13 to 23% for women. Interestingly, however, within each integrated occupation, women consistently required more duty-limited days then did men, with relative increases ranging from 27% (in the military police) to 57% in the medical occupation. These findings suggest that occupational differences in culture and job requirements may influence male and female soldiers’ time spent with lower limb limited duty, but that there is a relatively consistent effect of female gender across occupations. It is important to emphasize that the aggregated estimate that 13% of service days required lower limb limited duty does not represent the experience of the typical active-duty soldier. Seventy-five per cent of soldiers studied did not receive a lower limb profile, while 8% of soldiers required limited duty for at least 90% of their observed service time. This sizable high-utilization population dramatically influenced the overall proportion of limited-duty time. Still, even when excluding that large subset, the excess impact of lower limb injury among women in the aggregate was clear and consistent. Looking ahead, these findings signal the importance of continual surveillance of injuries and associated limited duty with the expansion of women’s roles in the US Army. As of 2 January 2016, an additional 220 000 previously male-only positions were opened to female soldiers [15,30]. It remains to be seen how injury rates and duty limitations will differ between men and women working in previously male-only specialities, such as infantry and special operations forces. The results of this study provide foundational pre-integration rates of lower-limb-related limited duty, and ongoing longitudinal assessment will allow continual analysis to provide training and administrative guidance for integrated military occupations. Key points An analysis of individual limited duty assignments (profiles) showed that 13% of service days for active-duty US Army soldiers (n = 568 753, 14% women) required limited duty for lower limb musculoskeletal injuries and related conditions in 2014. Injuries to the knee were responsible for 45% of these limited duty days. Within integrated military occupations, female soldiers experienced 27–57% more time on limited duty for lower limb musculoskeletal injuries and related conditions compared with men. Funding This study was supported by a grant from the US Army Medical Department Advanced Medical Technology Initiative, which had no role in study design; collection, analysis, or interpretation of data; writing the report; or the decision to submit the report for publication. Financial disclosure: No financial disclosures were reported by the authors of this article. Disclaimer: The views expressed in this article are those of the authors and do not reflect the views or official policies of the US Government, the Department of Defense, the Defense Health Agency, the Department of the Army, or the US Army Medical Command. Conflicts of interest None declared. Acknowledgements The authors would like to thank the thousands of US Army soldiers in the study population for their service to this country. This study was supported by an award from the FY 15 Army Medical Department Advanced Medical Technology Initiative. All data used in the study were provided under a cooperative agreement with the US Army Medical Command. References 1. Jones BH, Canham-Chervak M, Canada S, Mitchener TA, Moore S. Medical surveillance of injuries in the U.S. Military. Am J Prev Med  2010; 38( 1 Suppl): S42– 60. Google Scholar CrossRef Search ADS PubMed  2. Ruscio BA, Jones BH, Bullock SHet al.   A process to identify military injury prevention priorities based on injury type and limited duty days. Am J Prev Med  2010; 38: S19– S33. Google Scholar CrossRef Search ADS PubMed  3. Hauret KG, Bedno S, Loringer K, Kao TC, Mallon T, Jones BH. Epidemiology of exercise- and sports-related injuries in a population of young, physically active adults: a survey of military service members. Am J Sports Med  2015; 43: 2645– 2653. Google Scholar CrossRef Search ADS PubMed  4. Roy TC, Knapik JJ, Ritland BM, Murphy N, Sharp MA. Risk factors for musculoskeletal injuries for soldiers deployed to Afghanistan. Aviat Space Environ Med  2012; 83: 1060– 1066. Google Scholar CrossRef Search ADS PubMed  5. Bell NS, Mangione TW, Hemenway D, Amoroso PJ, Jones BH. High injury rates among female army trainees: a function of gender? Am J Prev Med  2000; 18: 141– 146. Google Scholar CrossRef Search ADS PubMed  6. Bijur PE, Horodyski M, Egerton W, Kurzon M, Lifrak S, Friedman S. Comparison of injury during cadet basic training by gender. Arch Pediatr Adolesc Med  1997; 151: 456– 461. Google Scholar CrossRef Search ADS PubMed  7. Knapik JJ, Sharp MA, Canham-Chervak M, Hauret K, Patton JF, Jones BH. Risk factors for training-related injuries among men and women in basic combat training. Med Sci Sports Exerc  2001; 33: 946– 954. Google Scholar CrossRef Search ADS PubMed  8. Altarac M, Gardner JW, Popovich RM, Potter R, Knapik JJ, Jones BH. Cigarette smoking and exercise-related injuries among young men and women. Am J Prev Med  2000; 18: 96– 102. Google Scholar CrossRef Search ADS PubMed  9. Knapik JJ, Graham B, Cobbs J, Thompson D, Steelman R, Jones BH. A prospective investigation of injury incidence and injury risk factors among Army recruits in military police training. BMC Musculoskelet Disord  2013; 14: 32. Google Scholar CrossRef Search ADS PubMed  10. Wentz L, Liu PY, Haymes E, Ilich JZ. Females have a greater incidence of stress fractures than males in both military and athletic populations: a systemic review. Mil Med  2011; 176: 420– 430. Google Scholar CrossRef Search ADS PubMed  11. Yates B, White S. The incidence and risk factors in the development of medial tibial stress syndrome among naval recruits. Am J Sports Med  2004; 32: 772– 780. Google Scholar CrossRef Search ADS PubMed  12. Boling M, Padua D, Marshall S, Guskiewicz K, Pyne S, Beutler A. Gender differences in the incidence and prevalence of patellofemoral pain syndrome. Scand J Med Sci Sports  2010; 20: 725– 730. Google Scholar CrossRef Search ADS PubMed  13. Reynolds K, Cosio-Lima L, Bovill M, Tharion W, Williams J, Hodges T. A comparison of injuries, limited-duty days, and injury risk factors in infantry, artillery, construction engineers, and special forces soldiers. Mil Med  2009; 174: 702– 708. Google Scholar CrossRef Search ADS PubMed  14. Feuerstein M, Berkowitz SM, Peck CAJr. Musculoskeletal-related disability in US Army personnel: prevalence, gender, and military occupational specialties. J Occup Environ Med  1997; 39: 68– 78. Google Scholar CrossRef Search ADS PubMed  15. U.S. Secretary of Defense. Implementation Guidance for the Full Integration of Women in the Armed Forces [Internet] . Washington, DC: U.S. Department of Defense, 2015. http://www.defense.gov/Portals/1/Documents/pubs/OSD014303-15.pdf (2 August 2017, date last accessed). 16. U.S. Department of the Army. Standards of Medical Fitness, Army Regulation 40–501. [Internet]. 2011. http://www.au.af.mil/au/awc/awcgate/army/r40_501.pdf (2 August 2017, date last accessed). 17. Jones BH, Bovee MW, Harris JMIII, Cowan DN. Intrinsic risk factors for exercise-related injuries among male and female army trainees. Am J Sports Med  1993; 21: 705– 710. Google Scholar CrossRef Search ADS PubMed  18. Allison KF, Keenan KA, Sell TC, Abt JP, McGrail M. Musculoskeletal, biomechanical, and physiological gender differences in the US military. Army Med Dep J  2015: 22– 32. 19. Beutler A, de la Motte S, Marshall S, Padua D, Boden B. Muscle strength and qualitative jump-landing differences in male and female military cadets: the jump-acl study. J Sports Sci Med  2009; 8: 663– 671. Google Scholar PubMed  20. Cowan DN, Bedno SA, Urban N, Lee DS, Niebuhr DW. Step test performance and risk of stress fractures among female army trainees. Am J Prev Med  2012; 42: 620– 624. Google Scholar CrossRef Search ADS PubMed  21. Gilchrist J, Jones BH, Sleet DA, Kimsey CD; CDC. Exercise-related injuries among women: strategies for prevention from civilian and military studies. MMWR Recomm Rep  2000; 49: 15– 33. Google Scholar PubMed  22. Hewett TE, Myer GD, Ford KRet al.   Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: a prospective study. Am J Sports Med  2005; 33: 492– 501. Google Scholar CrossRef Search ADS PubMed  23. Loringer K, Bedno S, Hauret K, Jones B, Kao T, Mallon T. Injuries from Participation in Sports, Exercise, and Recreational Activities Among Active Duty Service Members — Analysis of the April 2008 Status of Forces Survey of Active Duty Members [Internet] . Aberdeen, MD: U.S. Army Public Health Command; 2011. http://www.dtic.mil/dtic/tr/fulltext/u2/a560733.pdf (2 August 2017, date last accessed). 24. Kelly EW, Jonson SR, Cohen ME, Shaffer R. Stress fractures of the pelvis in female navy recruits: an analysis of possible mechanisms of injury. Mil Med  2000; 165: 142– 146. Google Scholar PubMed  25. Knapik JJ, Bullock SH, Canada Set al.   Influence of an injury reduction program on injury and fitness outcomes among soldiers. Inj Prev  2004; 10: 37– 42. Google Scholar CrossRef Search ADS PubMed  26. Hewett TE, Myer GD, Ford KR. Reducing knee and anterior cruciate ligament injuries among female athletes: a systematic review of neuromuscular training interventions. J Knee Surg  2005; 18: 82– 88. Google Scholar CrossRef Search ADS PubMed  27. Hill OT, Kay AB, Wahi MM, McKinnon CJ, Bulathsinhala L, Haley TF. Rates of knee injury in the U.S. Active Duty Army, 2000–2005. Mil Med  2012; 177: 840– 844. Google Scholar CrossRef Search ADS PubMed  28. Kaufman KR, Brodine S, Shaffer R. Military training-related injuries: surveillance, research, and prevention. Am J Prev Med  2000; 18: 54– 63. Google Scholar CrossRef Search ADS PubMed  29. Larsson H, Larsson M, Osterberg H, Harms-Ringdahl K. Screening tests detect knee pain and predict discharge from military service. Mil Med  2008; 173: 259– 265. Google Scholar CrossRef Search ADS PubMed  30. Army Public Affairs. Army Outlines Gender Integration Implementation Plan [Internet] . Washington, DC: U.S. Army; 2016. https://www.army.mil/article/163980/army_outlines_gender_integration_implementation_plan (2 August 2017, date last accessed). Published by Oxford University Press on behalf of The Society of Occupational Medicine 2017.

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Occupational MedicineOxford University Press

Published: Jan 1, 2018

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