Neuromuscular and Hormonal Factors Associated With Knee Injuries in Female Athletes

Timothy E. Hewett

Female athletes who participate in jumping and cutting sports are 4 to 6 times more likely to sustain a serious knee injury than male athletes participating in the same sports. More than 30,000 serious knee injuries are projected to occur in female intercollegiate and high school athletics in the US each year. The majority of these injuries occur by non-contact mechanisms, most often during landing from a jump or making a lateral pivot while running. Knee instability, due possibly to decreased neuromuscular strength and coordination or increased ligamentous laxity, may underlie the increased incidence of knee injury in females. Neuromuscular training can significantly increase dynamic knee stability in female athletes. Female sex hormones (i.e. estrogen, progesterone and relaxin) fluctuate radically during the menstrual cycle and are reported to increase ligamentous laxity and decrease neuromuscular performance and, thus, are a possible cause of decreases in both passive and active knee stability in female athletes. Oral contraceptives stabilise hormone levels during the menstrual cycle and may function to either passively or actively stabilise the knee joint. The long term objective of clinicians and researchers should be to determine the factors that make women more susceptible than men to knee ligament injury and to develop treatment modalities to aid in the prevention of these injuries. The immediate objectives of this review are to examine how female and male athletes differ in neuromuscular and ligamentous control of the lower extremity. The review will examine the effects of neuromuscular training on knee stability. The effects of female hormone levels and oral contraceptives on neuromuscular control of the female athletes' knee will also be discussed.