Relationship between knee joint laxity and knee joint mechanics during the menstrual cycle

Background: An increase in knee laxity during the menstrual cycle may increase the risk of anterior cruciate ligament injury. Objective: To investigate whether changing knee laxity during the menstrual cycle correlates with changing knee joint loads in a cutting manoeuvre. Design: Cross-sectional study. Setting: Laboratory testing. Participants: 25 healthy women, with a normal menstrual cycle, no history of oral contraceptive use, and no previous knee injury Interventions: Serum hormone concentrations were assessed and knee joint laxity at a load of 89 N was measured during the follicular, ovulation and luteal phases. Participants performed 10 trials of a cutting manoeuvre to quantify knee joint mechanics at each test session. Main outcome measurements: Knee joint laxity (mm), peak knee angle (degrees) and knee joint moment (Nm) and knee joint impulse (Nms). Results: Increased knee laxity was observed during ovulation compared with the luteal phase, but no significant changes in knee mechanics corresponding to menstrual phases were found. A positive correlation was found between changes in knee laxity and changes in knee joint loads (Delta moment or Delta impulse) from the follicular phase to ovulation, and from ovulation to the luteal phase (p<0.05). Women in whom knee laxity increased showed increased knee loads, and those in whom knee laxity decreased showed decreased knee loads during the menstrual cycle. Conclusions: Knee laxity correlates positively with knee joint loads, and increased knee laxity during the menstrual cycle may be a potential risk factor for anterior cruciate ligament injuries in certain women during sports activity.