Researchers at the University of Michigan and the Cincinnati Sports Medicine Clinic have discovered that female athletes are more likely to suffer a common type of knee injury when their estrogen levels are highest.
Knee injuries, especially damage to the anterior cruciate ligament (ACL), have been characterized as an epidemic among women. Studies have shown that women are two to eight times more likely than men to suffer ACL tears. Such injuries often require surgery and up to a year of rehabilitation.
Theories abound over why women suffer more knee
injuries, but there has been little objective proof. The U-M research team,
led by orthopaedic surgeon
Edward M. Wojtys, M.D., evaluated 40 young females with acute ACL injuries
and discovered a disproportionately high number of the injuries occurred
during the ovulatory phase of the athlete's menstrual cycle. The ovulatory
phase typically occurs during days 10-14 of the cycle and is marked by
a significant rise in estrogen levels as well as high levels of a hormone
Wojtys (pronounced VOY-tes) says these hormone fluctuations may be a significant factor in the high number of ACL tears suffered by women, although it has not been ascertained precisely how estrogen contributes to knee injuries. The researchers suspect estrogen and relaxin have profound effects on women's neuro-muscular systems and the mechanics of soft tissue such as ligaments and tendons. If that's true, other joints, including ankles and shoulders, might be affected the same way, says Laura Huston, co-author of the study and a research engineer at MedSport, a section of the U-M Medical Center's orthopaedic surgery department.
The link between ACL injuries and the hormonal cycle has big implications for female athletes and raises the question of whether that cycle can be manipulated. "Would a hormone supplement protect women?" Wojtys asks. "This study raises more questions than it answers - which will lead to a lot more research."
Wojtys will present the results Sunday, June 22, at the annual meeting of the American Orthopaedic Society for Sports Medicine in Sun Valley, Idaho. The study also found that:
61 percent of the ACL injuries suffered by the women in the study occurred during a game.
64 percent happened during the first 30 minutes of play.
The type of shoes worn was not a significant factor in these non-contact injuries.
The anterior cruciate ligament runs through the center of the knee joint and controls the pivoting motion of the knee. ACLs work with the leg muscles - hamstrings and quadriceps - to stabilize the knee. When they are stretched too far, however, they can tear - an injury which often occurs when an athlete plants her leg hard, then twists her body. ACL ruptures often occur during sports that require jumping and pivoting - such as basketball, soccer and volleyball.
It has been speculated that women are more susceptible to knee injuries because of physiologic characteristics such as wider hips which place greater pressure on the inside of the knee and less leg-muscle strength and endurance. Another theory suggests women's knees are more vulnerable because female athletes rely excessively on their quadricep muscles and too little on their hamstrings - perhaps as a result of incorrect training.