Photo courtesy of David Perrin and Sandra J. Schultz

U.Va. researchers are conducting several tests, using the device at right, which records muscle responses when a sudden motion makes participants attempt to stabilize the knee in response. Why female athletes tear the anterior cruciate ligament, pictured below, more often than males is the question U.Va. researchers are trying to answer.

When women get physical, knees take the brunt of it

By Ida Lee Wootten

Although women and girls have made great strides in sports, their knees may be paying a price.

Among high school, college and Olympic athletes, female players suffer substantially more knee injuries than men. Injuries to the anterior cruciate ligament (ACL), one of the primary stablizing ligaments inside the knee, usually require six to nine months down-time, which adds to athletes' physical and mental stress.

The injury happens more frequently in sports that require changing directions while running, cutting and landing from a jump, such as basketball and soccer. Finding out why female athletes suffer more ACL injuries than men and learning how to prevent such disabling occurrences are some of the hottest research topics in sports medicine and athletic training.

A collaborative effort at U.Va. may be on the verge of finding some answers. The National Institutes of Health has awarded researchers in the Curry School of Education's kinesiology department $222,000 to support its investigation into why females participating in interscholastic and intercollegiate sports experience injury to the anterior cruciate ligament at a higher rate than males.

The studies are probing the factors that may determine if females have less joint stability and, therefore, experience lower tolerance to stress on the knee joint. The central thrust of the research is to determine the role that gender and hormones play in ACL injuries and neuromuscular stability, according to principal investigator David Perrin, the Joe Gieck Professor of Sports Medicine and chair of the human services department, and study coordinator Sandra Shultz, a research assistant professor.

The researchers are taking blood samples daily from 20 collegiate females during one complete menstrual cycle to determine estrogen, progesterone and testosterone concentrations. The samples are drawn after the females participate in a ligament stress test that determines how much the joint is displaced when force is applied to it.

Twenty collegiate males serve as controls and are tested once every seven days over a 28-day period after undergoing the same testing.

To test the compliance of the knee, participants are placed in a Telos Device that applies force to the back of the calf, causing the lower leg to move forward relative to the thigh, stressing the anterior cruciate ligament.

The studies will help the researchers understand the relationship between hormone levels and how well the knee handles stress-loads. "Fluctuation of sex hormones during a women's menstrual cycle may have an impact on the ligament's compliance and how tight or how loose the knee is," said Perrin. He noted that preliminary studies have shown there is a difference in tightness and looseness of the knee during menstrual cycles.

The next step in the research could be to determine a link between injury risk and elevations of hormones, Perrin and Shultz said.

If a link is found, injuries could be prevented through several strategies. One possibility would be to change women's hormone levels through birth control pills. Another possibility would be engaging in training programs to improve muscular control and knee protection. Still another would be to start intervention strategies each month before female athletes start their menstrual cycles.

"The work has lots of promise," said Perrin, who chaired a symposium on the topic at an American College of Sports Medicine conference last June.

"Even if a link is not established, the research is important because it is likely to determine what other factors come into play," Perrin said.

The investigation is based on Perrin's and Shultz's ongoing research into how gender and lower extremity limb alignment affect muscle reflex times and activation patterns. Supported by approximately $53,500 to date from the National Athletic Trainers Association, the studies are trying to determine how quickly and efficiently knee muscles respond to joint stress.

To test muscle responses, they designed a "lower extremity perturbation device" that produces a sudden, unanticipated forward rotation of the trunk and femur on the weight-bearing tibia. After experiencing the perturbation, muscle responses are recorded as the test participants attempt to stabilize the knee. Participants complete 10 trials of both internal and external rotation; muscle activity and response time are measured for analysis.

The researchers have found that females tend to activate the front thigh muscles faster than males, which may increase the stress placed on the ACL. One factor that may explain the gender disparity in sports-related injuries is differences in lower extremity limb alignment, Shultz and Perrin believe. As a follow-up to this study, they are evaluating the influence of excessive knee angulation and flattened arches in feet, alignment faults commonly seen in females due to their wider pelvises, on activation patterns at the knee.

With support from the Health System's General Clinical Research Center, the studies are being conducted in the Sports Medicine/Athletic Training Research Laboratory in the kinesiology department of U.Va.'s Curry School of Education. The Curry School researchers, including Brent Arnold and Bruce Gansneder, are collaborating with other colleagues across Grounds: Arie Rijke in materials science and engineering, Susan Kirk in endocrinology, and Kevin Granata in orthopedics and biomedical engineering.