The University Record, July 16, 1997

Link found between knee injuries and estrogen levels in women athletes

From Medical Center Public Relations

Researchers at the U-M 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, 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 called relaxin.

Wojtys 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 neuromuscular 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.

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 that 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.

Women may be 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.

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."

The study also found that:

Wojtys presented the results of the study June 22 at the annual meeting of the American Orthopaedic Society for Sports Medicine.