The Relationship Between Menstrual Cycle Phase and Anterior Cruciate Ligament Injury

A Case-Control Study of Recreational Alpine Skiers

Bruce Beynnon. The American Journal of Sports Medicine. Vol. 34, No. 5. 2006

It has been made evident that male athletes suffer more ACL injuries compared to females. However, when comparing the incidence rate of ACL tears amongst female and male athletes participating in the same sport, females suffer more ACL injuries. In fact, the National Collegiate Athletic Association statistics illustration that woman are between 2 and 8 times more likely to sustain an ACL injury than men participating in the same sport.

There is great correlation between ACL injuries and dramatic loss of function at the knee, as well as future osteoarthritis. The purpose of this study was to identify any risk factors that may increase a person’s susceptibility to knee injuries and whether these risks factors remain constant over time or change in a cyclic manner. If the latter, it is crucial to understand the pattern of change. More specifically, this study focused on whether or not changes in the menstrual cycle alter the risks for ACL injuries. The hypothesis presented in this study is that the likelihood of suffering an ACL injury is directly affected by the phase of the menstrual cycle. The two study groups consisted of female alpine skiers with ACL disruptions and uninjured control skiers. Researchers collected their estrogen and progesterone concentrations at the time of injury and later determined the phase of the menstrual cycle at which the ACL injury took place. A questionnaire was filled out by both injured and controlled subjects, which included athletic participation in skiing, injury history, and menstrual history. Blood samples were taking from the injured subjects 2 hours after injury and upon enrollment of the control subjects. A total of 46 female alpine skiers sustained an ACL tear and therefore took part in this study. A total of 45 females were uninjured and acted as the control group, yielding a total of 91 participants. Researchers sampled serum from the participants at the time of the injury and used progesterone concentrations to group subjects into either preovulatory or postovulatory phases of the menstrual cycle. Amongst the subjects in the ACL tear category, 74% were in the preovulatory phase of the menstrual cycle at the time of injury and 56% of females in the control group were in the preovulatory phase at the time of testing. The study concluded that females are 3 times more likely to have an ACL tear while in the preovulatory phase compared to the postovulatory phase, this result being statistically significant.

It is important to note that this study was designed as a case-control study that investigated the relationship between menstrual cycle phase and ACL injuries through retrospective data because subjects are accounted for after sustaining a knee injury.

Further studies should be done that focus on estrogen and progesterone as predisposing factors in the increased incidence of ACL injuries. The current study mentioned that estrogen receptors are found on the human ACL. When tested on rabbits, an increase of serum levels of estrogen influences the failure strength of the ACL. This is concerning for athletic women because high levels of estrogen may affect the ligament, leading to an increased incidence of ACL tears.

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