Influence of gender, estrogen and exercise on anterior knee laxity.

BACKGROUND Researchers have theorized that the disproportionate number of anterior cruciate ligament injuries in females, as compared to males, may be related to knee laxity, which in turn may be influenced by hormones. The purpose of this study was to investigate the collective effects of gender, estrogen and exercise on knee laxity. METHODS Subjects consisted of 12 females and 12 males with no history of lower extremity injury. Serum estrogen levels and knee laxity were measured for the female subjects at specific times to represent three menstrual cycle phases while knee laxity of the male subjects was measured on three different days. For each data collection session, knee laxity was measured just prior to and immediately following an exercise protocol. Separate repeated measures ANOVAs were used to compare estrogen levels across the phases and analyze the laxity data. FINDINGS Females exhibited greater knee laxity than males both pre- and post-exercise across all phases of the menstrual cycle. Estrogen fluctuations across the menstrual cycle did not modify knee laxity in females. Prior exercise induced equivalent increases in knee laxity in males and females across the data collection periods and irrespective of estrogen concentration. INTERPRETATION If the anterior cruciate ligament is more distensible during athletic activities, it may be less capable of providing the necessary stability in order to prevent injury. This decreased stability may be contributing to the female athlete's increased incidence of anterior cruciate ligament injury. Overall, if females experience greater knee laxity during athletic activities, specific training strategies to compensate for these differences are warranted.