The Effects of Oral Contraceptive Use on Ligamentous Injury Incidence in Females: A Potential for Prevention
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Female athletes have higher incidence of anterior cruciate ligament (ACL) injury compared to males among sports requiring lower limb agility such as soccer and basketball. Often blamed on sex differences in biomechanics and neuromuscular control, current literature has failed to demonstrate specific mechanisms capable of explaining sex-related differences injury rates. Consequentially, techniques intended to prevent ACL injury in female athletes, primarily strength and conditioning programs, have yielded mixed results. Alternatively, sex hormone differences between the sexes, specifically serum estrogen levels, appears to be an underlying cause for differences in ACL injury rates. In relation to the menstrual cycle, female athletes sustain more ACL injuries than expected during the first 14 days of the cycle (follicular and ovulatory phases) and less injuries than expected during the last 14 days (luteal phase). Increased serum estrogen levels increase ACL laxity and potentially are to blame for an increased injury risk. Estrogen receptors located within human ACL fibroblasts, when activated, decrease collagen production, which leads to decreased ligament strength and increased laxity. Estrogen levels and knee joint laxity are greatest during the phases of the menstrual cycle in which ACL injury is over-represented. In theory, a reduction in serum estrogen levels should increase and stabilize ACL strength in females, potentially reducing injury risk. Hormonal contraceptives, through their negative feedback function, reduce estrogen levels. We hypothesize that females using oral contraceptives (OCs) will have lower rates of ACL injury compared to nonusers. To assess this relationship we performed a case-control study using national commercial insurance claims data. Cases were defined as females undergoing ACL reconstruction and OC use was determined from a 12 month history of OC prescription fulfillment previous to reconstruction or matched index date. We found that in females aged 15-19 years, the ages with the highest ACL injury incidence, OC users were 18% less likely to undergo ACL reconstruction than OC nonusers. This is the first evidence suggesting protection from injury among OC users and it creates a foundation for future prospective efforts. We conclude that OC use may help prevent ACL injury in specific female populations.