Epidemiology of Lower Extremity Stress Fractures in the United States Military.

Purpose: To comprehensively quantify established risk factors for the development of lower extremity stress fractures within a contemporary U.S. military cohort.

Methods: Using the Defense Medical Epidemiological Database, all U.S. service members diagnosed with tibia/fibula, metatarsal, other bone, femoral neck, and femoral shaft stress fractures were identified based on International Classification of Diseases, 9th Revision, Clinical Modification code from 2009 to 2012. Incidence rates (IRs) and adjusted IRs controlling for sex, race, age, rank, and branch of service were obtained with multivariate Poisson regression analysis.

Results: Between 2009 and 2012, 31,758 lower extremity stress fractures occurred among 5,580,875 person-years, for an unadjusted IR of 5.69 per 1,000 person-years. Tibial/fibular (40%) involvement was the most common. Bimodal age distribution revealed that service members under 20 years old (23.06; 95% confidence interval [CI] 22.52, 23.55) or ≥40 (6.86; 95% CI 6.65, 7.07) had greatest risk. Females were at higher risk for total lower extremity (3.11; 95% CI, 3.03, 3.18). White service members were also more at risk than Black service members (p < 0.0001). The majority of stress fractures (77.5%) occurred in junior enlisted service members, with the Army and Marines most at risk.

Conclusion: This investigation elucidates several nonmodifiable risk factors for stress fractures in the military and may inform screening measures to reduce this significant source of disability.