The Menstrual Cycle’s Effect on ACL Injury Rates

It is well-established that female athletes are at a 4-10x higher risk of developing injuries to the anterior cruciate ligament (ACL) compared to their male counterparts (1). These injuries are immediately disabling, require long-term rehabilitation, and carry the risk of life-long consequences such as increased risk of reinjury and posttraumatic osteoarthritis. Yet ACL injuries continue to be one of the most common musculoskeletal injuries in female athletes. Studies have shown that as many as one in ten Division I college female athletes will suffer from an ACL tear during their athletic career (2). 

By understanding the underlying causes which increase injury risk, medical specialists and athletes can anticipate individual risk-levels and develop individual preventative training programs. While research is ongoing, scientists believe that anatomical and hormonal differences play a key role in why females are at such a high risk compared to males (1). Varying levels of estradiol and progesterone have been linked to changes in joint laxity and strength (3). Estradiol and progesterone levels are at their lowest during the menses, corresponding approximately with days 1-6 of the menstrual cycle. Estradiol peaks initially during ovulation and has a second, lower peak during the luteal phase, while progesterone peaks during the mid-luteal phase. Recent studies have investigated whether the menstrual cycle and hormonal shifts that accompany it have a significant effect on the practical risk of injury. 

By collecting data on last menstruation and saliva-samples from female athletes who sustained recent ACL injuries, researchers found that risk of injury is not random, but rather peaks during the first two days after the onset of menses and during ovulation (4). These time periods coincide with two of the lowest concentrations of estradiol and progesterone during the menstrual cycle. All participants in this study had a regularly occurring menstrual cycle not altered or controlled by oral contraceptives. Analyzing the studies published thus far also suggests that the lowest risk of injury is during the luteal phase (5). This research suggests that hormonal differences may account for one of the most addressable risk factors in female athletes. While physiological differences are not easily changed or addressed, hormonal cycles can be safely manipulated with the use of medication and the guidance of physicians. This raises the question of whether hormonal birth controls that alter the menstrual cycle could offer any protection against ACL injuries in athletes. 

A meta-analysis of seven studies on the effect of hormonal birth control on ACL injury rates found that oral contraceptives can offer up to a 20% reduced risk in ACL injury. The high level of progesterone in most oral contraceptives may offer the greater joint strength and reduced passive joint laxity usually seen during the luteal phase of the menstrual cycle (5, 6). Further long-term studies are required to fully understand the efficacy of oral contraceptives for ACL protection and the mechanism of action through which they offer such. However, for at-risk athletes, if oral contraceptives fit into their lifestyles, this may offer an incredibly accessible and low-risk option to try in coordination with strength training and physical therapy to reduce the risk of ACL injury (assuming it is made clear that there is no definitive data demonstrating the efficacy of using oral contraceptives to prevent ACL injuries). 

While further research is needed to understand the full effect that the menstrual cycle has on ACL injury risk, it is important for high-risk athletes (such female soccer, hockey, and volleyball players) to regularly engage in ACL-protection activities in coordination with a physical therapist, orthopedist, or sports medicine specialist. It can also be of immense value to use a biofeedback mechanism, such as Esurgi’s JointSpy, to identify risky behavior and movements. Real time feedback from JointSpy allows athletes and coaches to implement the proper exercise routines and movement corrections to decrease injury risk.

Sources:

1. Smith, H. C., Vacek, P., Johnson, R. J., Slauterbeck, J. R., Hashemi, J., Shultz, S., & Beynnon, B. D. (2012). Risk factors for anterior cruciate ligament injury: a review of the literature-part 2: hormonal, genetic, cognitive function, previous injury, and extrinsic risk factors. Sports health, 4(2), 155–161. https://doi.org/10.1177/1941738111428282
2. McDaniel, L. W., Rasche, A., Gaudet, L., & Jackson, A. (2010, March). Reducing The Risk Of ACL Injury In Female Athletes. Contemporary Issues In Education Research, 3(3), 15-20. https://files.eric.ed.gov/fulltext/EJ1072598.pdf
3. Somerson, J. S., Isby, I. J., Hagen, M. S., Kweon, C. Y., & Gee, A. O. (2019). The Menstrual Cycle May Affect Anterior Knee Laxity and the Rate of Anterior Cruciate Ligament Rupture: A Systematic Review and Meta-Analysis. JBJS reviews, 7(9), e2. https://doi.org/10.2106/JBJS.RVW.18.00198
4. Slauterbeck, J. R., Fuzie, S. F., Smith, M. P., Clark, R. J., Xu, K., Starch, D. W., & Hardy, D. M. (2002). The Menstrual Cycle, Sex Hormones, and Anterior Cruciate Ligament Injury. Journal of athletic training, 37(3), 275–278.
5. Herzberg, S. D., Motu’apuaka, M. L., Lambert, W., Fu, R., Brady, J., & Guise, J. M. (2017). The Effect of Menstrual Cycle and Contraceptives on ACL Injuries and Laxity: A Systematic Review and Meta-analysis. Orthopaedic journal of sports medicine, 5(7), 2325967117718781. https://doi.org/10.1177/2325967117718781
6. Myer, G. D., Ford, K. R., Paterno, M. V., Nick, T. G., & Hewett, T. E. (2008). The effects of generalized joint laxity on risk of anterior cruciate ligament injury in young female athletes. The American journal of sports medicine, 36(6), 1073–1080. https://doi.org/10.1177/0363546507313572