The Relationships of the Menstrual Cycle and Anterior Cruciate Ligament (ACL) Injuries in Female Downhill Skiers
Presented at the American Orthopaedic Society for Sports Medicine, 2000

Melbourne D. Boynton, M.D.
Jo Hannafin, M.D., Ph.D.
Jim Jordan, M.D.
Jim Russell, M.D.

Objective: The purpose of this study is to determine the relative risk of an anterior cruciate ligament rupture in female downhill skiers during the different phases of the menstrual cycle.

Methods: During the 1998-1999 and 1999-2000 ski seasons, any woman who presented to our on-mountain medical clinic with a newly ruptured ACL in a previously healthy knee was asked to participate in this study. Highly experienced physicians made the diasnosis of ACL injury by physical exam and history. The subjects completed a questionnaire regarding exact menstrual history, cycle length, use of oral contraceptives, and past medical history. Patients were contacted one month later to confirm the diagnosis of ACL tear and to obtain the onset date of their next menstruation.

Results: During the study period, 102 women were diagnosed with acute ACL rupture, 21 of whom were excluded due to abnormal medical histories, irregular menstrual cycles, unconfirmed ACL tears, or incomplete follow-up. A normal cycle was defined as having a duration of 22 to 34 days. 81 women with acute ACL injury and normal, regular and average menstrual cycle length was 28.5 +/- 2.5 days. 26/81 women used oral contraceptives.

In this study, the date of presumptive ovulation was calculated as occurring 14 days prior to the onset of the menstrual period following the injury (day -14). The ovulatory phase was defined as days (-14) to (-18). For the overall group, 32/81 injuries occured during the follicular phase, 18/81 occured during the ovulatory phase, and 31/81 occurred during the luteal phase. In the 55 patients not using oral contraceptives, 43.6% (24/55) of injuries occurred during the follicular phase, 20% (11/55) occurred during the ovulatory phase, and 36.4% (20/55) occurred during the luteal phase. A Chi-square test for homogeneity was used to determine if the rate of injury observed during each phase was significantly different that what was expected to occur by chance. There was no statistically significant variation in ACL injury rate based on phase of menstrual cycle in either the oral contraceptive or non-oral contraceptive groups.

Conclusions: The study demonstrates that there is no statistically significant increase in the risk of ACL rupture in female downhill skiers during any one phase of the menstrual cycle.