• Bruce D Beynnon, Robert J Johnson, Stuart Braun, Mike Sargent, Ira M Bernstein, Joan M Skelly, and Pamela M Vacek.
• Department of Orthopaedics & Rehabilitation, McClure Musculoskeletal Research Center, Stafford Hall, Room 438A, University of Vermont, Burlington, VT 05405-0084, USA. bruce.beynnon@uvm.edu
• Am J Sports Med. 2006 May 1; 34 (5): 757-64.

BackgroundFemale athletes suffer a greater incidence of anterior cruciate ligament tears compared with male athletes when participating in common sports; however, very little is known about the factors that explain this disparity.Study DesignCase-control study; Level of evidence, 3.MethodsFemale recreational alpine skiers with an anterior cruciate ligament rupture and age-matched control skiers provided a serum sample and self-reported menstrual history data immediately after injury. Both serum concentrations of progesterone and menstrual history were then used to group subjects into either preovulatory or postovulatory phases of the menstrual cycle.ResultsAnalysis of serum concentrations of progesterone revealed that alpine skiers in the preovulatory phase of the menstrual cycle were significantly more likely to tear their anterior cruciate ligaments than were skiers in the postovulatory phase (odds ratio, 3.22; 95% confidence interval, 1.09-9.52; P = .027). Analysis of menstrual history data found similar results, but the difference was not statistically significant (odds ratio, 2.38; 95% confidence interval, 0.86-6.54; P = .086).ConclusionThe likelihood of sustaining an anterior cruciate ligament injury does not remain constant during the menstrual cycle; instead, the risk of suffering an anterior cruciate ligament disruption is significantly greater during the preovulatory phase of the menstrual cycle compared with the postovulatory phase.Clinical RelevancePhase of menstrual cycle may be one of the risk factors that influence knee ligament injury among female alpine skiers. The findings from this study should be considered in subsequent studies designed to identify persons at risk for anterior cruciate ligament injury and to develop intervention strategies.

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