Sex Differences in the Incidence and Risk of Ankle-Foot Complex Stress Fractures Among U.S. Military Personnel

Abstract

Background: The objective of this study was to evaluate sex differences in the incidence and risk of ankle–foot complex (AFC) stress fractures among U.S. military personnel, which could assist in developing management strategies as females assume a greater role in U.S. military operations. Methods: The Defense Medical Epidemiological Database was used to identify all diagnosed AFC stress fractures in military personnel from 2006 to 2015. Cumulative incidence of AFC stress fractures was calculated and compared by year, service branch, and military rank. Sex differences in the risk of AFC stress fractures by occupation were examined, and integrated (i.e., male and female) occupations were compared with non-integrated (i.e., male–only) occupations. Results: A total of 43,990 AFC stress fractures were identified. The overall incidence rate was 2.76 per 1,000 person-years for males and 5.78 per 1,000 person-years for females. Females consistently had higher incidence of AFC stress fractures across all subgroups, particularly among enlisted personnel. Female enlisted service members had the highest risk of AFC stress fractures in aviation [relative risk (RR) = 5.74; 95% confidence interval [CI] 4.80–6.87] and artillery/gunnery (RR = 5.15; 95% CI 4.62–5.75) occupations. Females in integrated occupations had significantly higher rates of AFC stress fractures than males in both integrated and non-integrated occupations (i.e., special forces, infantry, and mechanized/armor). Conclusions: Females in the U.S. military have a higher risk of AFC stress fractures than males. As integration of females into previously sex-restricted occupations continues, focused prevention efforts may be needed to reduce injury burden and maximize medical readiness.