Ethinyl Estradiol-Containing Hormonal Contraceptive Prescriptions are Associated with Reduced Stress Fracture Risk in Female Soldiers

Abstract

Stress fractures are common injuries among military personnel, and female recruits have an approximately three times greater risk for stress fracture than their male counterparts. Due to positive effects on bone metabolism in amenorrheic and energy deficient athletes, it has been suggested that hormonal contraceptive use may reduce the risk for stress fractures. However, benefits of hormonal contraceptives remain controversial. PURPOSE: We aimed to determine the stress fracture risk associated with hormonal contraceptive prescriptions in female U.S. Army soldiers. METHODS: We conducted a retrospective cohort study using data from the Total Army Injury and Health Outcomes Database from 2002 to 2011. We identified female soldiers who had stress fractures at the lower extremity and pelvis (n=18,531; mean age 22.93 ± 5.57 yrs). Soldiers with a stress fracture were matched with 4 controls (n=74,124; mean age 23.34 ± 5.78 yrs) by length of time in the military on the date of stress fracture. We recorded contraceptive prescriptions within 6 months of stress fracture diagnosis. Conditional logistic regression was used to calculate the odds ratios (OR) and 95% confidence intervals (CI) for stress fracture with adjustment for age, race, ethnicity, and education level. Risk of stress fracture was determined for soldiers prescribed oral combination (ethinyl estradiol and progestogen) contraceptives (n=10,898), non-oral combination (ethinyl estradiol and progestogen) contraceptives (n=775), and progestogen-only contraceptives (n=220). RESULTS: Stress fracture risk was 25%-29% lower in soldiers prescribed oral (OR=0.75, 95% CI [0.71, 0.080]) and non-oral (OR=0.71, 95% CI[0.58, 0.87]) combination contraceptives. Progestogen-only contraceptives prescriptions had no effect on stress fracture risk (OR=0.94, 95% CI [0.66, 1.33]). CONCLUSION: This large study, with over 90,000 women, suggests ethinyl estradiol-containing contraceptives may have a protective effect on developing stress fractures. Prospective studies are needed to verify these results and identify the underlying mechanisms of this protective effect. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.