Musculoskeletal injuries (MSKIs) are highly prevalent in the U.S. military, especially among high-performing service members such as Marines. MSKI episodes occurred at a rate of 1,004.73 episodes per 1,000 person-years in U.S. Marines between December 2016 and August 2021.¹ In garrison, these conditions pose a substantial threat to operational readiness, affecting service members’ ability to train and deploy to meet unit and national objectives.¹ MSKIs, which include both macrotraumatic (categorized as injury/poisoning) and repetitive microtraumatic (categorized as musculoskeletal disease) diagnostic categories, are the leading medical conditions in the Military Health System (MHS) and affect more service members than any other category.² This does not change when service members deploy.³ When macrotraumatic and repetitive microtraumatic diagnostic categories are combined, MSKIs are the leading medical conditions that result in medical evacuation of deployed service members out of the operational theater.⁴ The most recent finding of MSKI as a leading nonbattle injury and reason for medical evacuation is consistent with the findings reported by Cohen and colleagues in 2010,⁵ who also found that U.S. Marines had the lowest return-to-duty rates following evacuation among the service branches deployed to the Iraq and Afghanistan conflicts.

Female service members have greater injury risk than their male counterparts in the same occupation for various musculoskeletal conditions in the lower extremity.^1,6–11 This is likely a result of not only biomechanical and physiological factors, but also psychosocial determinants of care-seeking following the onset of symptoms or injury-related impairment.^1,6–14 The evidence suggests that military occupations not only have varying physical loads and environmental exposures that may affect injury risk, but also unique cultures that may influence care-seeking.^7,9–14 This is especially true within combat arms occupations in the Fleet Marine Force.

To project power in austere, uncertain, and arduous conditions under the threat of harm at “the tip of the spear,” ground combat occupations are composed of service members that are proactive, mission centered, highly resilient, and have substantial grit. Not dissimilar to care-seeking behaviors in athletes, service cultures within combat arms likely promote self-management and reduce care-seeking following injury.¹² The cultural factors in ground combat occupations that preclude care-seeking may plausibly counteract the positive care-seeking behaviors typically observed in women. Given that female service members have only been assigned to ground combat roles since December 2015,¹⁵ evaluation of sex and MSKI risk in ground combat occupations has not been possible until there was an ample population to study. Therefore, the purpose of this population-level epidemiological study was to assess (1) if female sex was a salient risk factor for MSKI in Marines serving in different military occupations, including combat arms, and (2) the effects of the integration period on MSKI risk among female Marines. We hypothesized that female service members would demonstrate greater musculoskeletal injury risk compared with male service members, particularly in combat occupations. Due to the changes in occupational and training exposure following the policy change, which likely had service-wide effects, we anticipated that there would be higher risk of MSKI in female Marines in the post-integration period compared with the pre-integration period.