Anterior knee laxity in young women varies with their menstrual cycle.

We studied 16 women 21-23 years old with regular menstrual cycles (28+/-4 days) and no history of knee injury. From their basal body temperatures and the serum concentrations of estradiol and progesterone, the follicular, ovulatory, and luteal phases were delineated. Using a KT-2000 arthrometer, anterior displacement at 89 N and 134 N and anterior terminal stiffness (N/mm) at 134 N were measured two or three times every week over a 4-week period. Eight men 21-23 years old were also measured. In women the anterior displacement at 89 N varied between the follicular and the ovulatory phase and between the follicular and the luteal phase ( P<0.05) and at 134 N between the follicular and the luteal phase ( P<0.05). There were no statistical differences in the anterior displacement with time in men, nor in anterior terminal stiffness in either sex. We conclude that anterior cruciate ligament laxity in women might be dependent on the concentrations of hormones.