Periodicity of noncontact anterior cruciate ligament injuries during the menstrual cycle

Background: Approximately 80,000 anterior cruciate ligament (ACL) tears occur per year in the United States. The majority of all ACL injuries are thought to be noncontact in nature with no clear mechanism of injury present. The increased rate of noncontact ACL injury in female athletes as compared to male athletes in some sports is well-documented. It explains an interest in the biochemical components as a predisposition to sustain an injury. Objective: The goal of this study was to analyze the 28-day periodicity of noncontact ACL injuries in female athletes taking and not taking oral contraceptives (OCs). Design: From 1996 to 1999, a descriptive project in the National Collegiate Athletic Association and National Association of Intercollegiate Athletics member schools allowed for an assessment of the commonality in the characteristics of the noncontact-ACL-injured athletes. Subjects: Of the 128 female athletes, 83 satisfied the study inclusion criteria. Twenty-five of the subjects represented the "On-Pills" subgroup and 58 of them represented the "Off-Pills" subgroup. Methods: The data were collected directly from the athletes by the certified athletic trainer at the school. Statistical Analysis: Centered moving average with a span of four days as well as linear and nonlinear regression were used to analyze the data. Results: A significant 28-day periodicity of injuries was present in the entire population as well as in the two subgroups. High- and low-risk time intervals were associated primarily with follicular and luteal phases. There was a significant difference in the time dependency of the number of injuries between the two subgroups: female athletes taking OCs demonstrated a greater difference between high and low risks, with a high-risk period shifted toward the beginning of the cycle. Conclusion: There is a significant relationship between the occurrence of a noncontact ACL injury and the collegiate athlete's menstrual cycle regardless of oral contraceptive use status.