Are Women Weaker in the Knees?
Society for Women's Health Research
November 15, 2001
It was an important game against a big rival and the Garnets were gaining momentum. Caitlyn Ryland, then 20 years old, jumped up for a rebound. When she came down, her knee gave out under her. She fell to the court, crying in pain and fear.
Adrienne Shibles, head women's basketball coach at Swarthmore College in Pennsylvania, knew immediately what had happened. "After you see it enough, you just know what it is by the scream," said Shibles. "They go down, it's dramatic, and they scream."
Ryland had torn her anterior cruciate ligament (ACL) - a tough band of tissue stretching from the thighbone to the shinbone that stabilizes the knee joint. She would sit out the rest of the season, and undergo ACL reconstructive surgery followed by months of physical therapy to get back on her feet.
Ryland is not alone in her injury. Orthopaedists, coaches, and researchers all agree that anterior cruciate ligament tears among female athletes have grown to epidemic proportions. "ACL injuries are a huge problem with enormous financial and health consequences," says Elizabeth Arendt, M.D., of the University of Minnesota in Minneapolis, where she serves as medical director of varsity athletics.
A slew of studies published during the past decade have shown that women are two to eight times more apt to rupture their ACL than men who play the same sports. The majority of these injuries occur in females aged 15 to 25, according to the American Academy of Orthopaedic Surgeons (AAOS.) Young women who play sports involving rapid pivoting, jumping, and sudden stops and starts (such as basketball, soccer and volleyball) are particularly vulnerable to ACL injury.
Despite numerous studies on the subject, experts still do not have the answer to the fundamental question of why women are at greater risk. There are, however, three main schools of thought on the issue, according to Laura Huston, senior research associate in the department of orthopaedics at the University of Michigan in Ann Arbor. Anatomical factors such as hip width and knee angle, biomechanical factors such as muscle strength and the hormonal influences of estrogen fluctuations have all been shown to play a potential role in increasing a woman's risk of ACL injury.
Results of a study presented at the recent 68th Annual Meeting of the AAOS in San Francisco provide an additional piece of this complex puzzle. Led by orthopaedic surgeon Edward Wojtys, MD, a team of University of Michigan researchers, including Huston, examined male and female college-aged athletes to see how well they were able to "protect" their anterior cruciate ligament when their lower leg was rotated.
Using a swivel platform in the laboratory, the researchers attempted to mimic a scenario in which the ACL is likely to be torn. Each athlete sat in a chair with his/her foot on the revolving platform. The researchers measured how much the knees rotated when their hamstring and quadriceps muscles were relaxed and then how much the knees rotated when their muscles were contracted. By contracting the hamstrings and quadriceps, an athlete can increase the stiffness of the knee, protecting it from potentially damaging knee rotation. In essence, the investigators were evaluating the athletes' ability to increase the stability of the knee joint when the knee was rotated.
Twenty-four athletes (12 male, 12 female) who participated in high-risk sports for ACL injury were compared with 28 athletes (14 male, 14 female) who competed in non-pivoting sports such as running and cycling. All athletes were matched for age, height, weight and fitness level.
The researchers observed a significant gender difference in ability among the study population. Overall, female athletes were not able to protect their knees as well as their male counterparts. Specifically, female athletes in pivoting sports did significantly worse than men who competed in pivoting sports. In addition, the researchers were surprised to find that women who competed in high-risk sports for ACL injury increased the stiffness of their knees significantly less than women who participated in non-pivoting sports.
"You would expect athletes who are constantly pivoting and cutting to be able to control these muscles better than women who practice other techniques [in other sports], Huston said. "But we didn't find that in females." The Michigan team did observe that males in pivoting sports were better able to control the rotation of their knee than their male counterparts in other sports.
So how does Huston explain this gender discrepancy? At this point, she can only speculate. There may be something vastly different in the male and female training programs for these sports, theorized Huston. As a result the muscles in women may not be equally prepared to handle the strain of jumping, quick starting, and pivoting. As a consequence, young female athletes may succumb to ACL injuries more readily than males who participate in the same sports.
Huston stresses, however, that the training component may be just part of the picture. "These results highlight another important element to add to our list of factors that may play a role in knee injuries in women," says Huston.
Other studies performed by the Michigan team have also pointed to the importance of the biomechanics of muscles around the knee in cases of ACL injury among women. Some of the most important findings are as follows:
- Women athletes tend to land with a straighter knee when jumping than do male athletes. This landing positioning may put more strain on a women's anterior cruciate ligament.
- Female athletes tend to rely on their quadriceps muscles more than their hamstrings to protect their knee joint as compared with men who play the same sports. Contracting the hamstrings tends to relieve ACL strain making it less apt to tear. As such, a woman athlete's tendency to use her quadriceps may increase her risk for ACL tear.
But experts like Dr. Arendt warn that the debate is far from over. "We only have very limited data from studies that are not randomized, nor tightly controlled," says Dr. Arendt. In addition, many of the studies have been conducted in the lab. Whether or not the results will translate to the basketball court is anyone's best guess.
In the meantime, coaches, trainers and physical therapists are gradually becoming better educated at training athletes. Many teams have implemented year-round weight training and conditioning programs. In addition, athletes are more apt to participate in sport-specific skill drills that train the body for safe positioning, balance and agility.
© June 2003 Society for Women's Health Research