Knee and hip loading patterns at different phases in the menstrual cycle: implications for the gender difference in anterior cruciate ligament injury rates

BACKGROUND: Menstrual cycle phase has been correlated with risk of noncontact anterior cruciate ligament injury in women. The mechanism by which hormonal cycling may affect injury rate is unknown. HYPOTHESES: Jumping and landing activities performed during different phases of the menstrual cycle lead to differences in foot strike knee flexion, as well as peak knee and hip loads, in women not taking an oral contraceptive but not in women taking an oral contraceptive. Women will experience greater normalized joint loads than men during these activities. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty-five women (13 using oral contraceptives) and 12 men performed repeated trials of a horizontal jump, vertical jump, and drop from a 30-cm box on the left leg. Lower limb kinematics (foot strike knee flexion) and peak externally applied moments were calculated (hip adduction moment, hip internal rotation moment, knee flexion moment, knee abduction moment). Men were tested once. Women were tested twice for each phase of the menstrual cycle (follicular, luteal, ovulatory), as determined from serum analysis. An analysis of variance was used to examine differences between phases of the menstrual cycle and between groups (alpha = .05). RESULTS: No significant differences in moments or knee angle were observed between phases in either female group or between the 2 female groups or between either female group and the male controls. CONCLUSIONS: Variations of the menstrual cycle and the use of an oral contraceptive do not affect knee or hip joint loading during jumping and landing tasks. CLINICAL RELEVANCE: Because knee and hip joint loading is unaffected by cyclic variations in hormone levels, the observed difference in injury rates is more likely attributable to persistent differences in strength, neuromuscular coordination, or ligament properties.