Charles A. Peterson, M.D,
Charles A. Peterson II, MD.

As women become increasingly involved in a wider variety of sports, the frequency and severity of athletic injuries seen in our female patients is also increasing. One of the most dramatic changes we've noted involves injuries to the anterior cruciate ligament (ACL). Twenty years ago it was fairly rare to see a female patient with an ACL injury , but it is very common now.

In the last 2 decades, female participation in athletics has increased dramatically, partly due to the Title IX act of 1972 (equal opportunity) with more federal funds available for women in college sports. In addition, evolving cultural and social norms have encouraged female participation in sports. There was a 50 percent increase in the number of women involved in collegiate soccer between 1989 and 1995. Women's professional sports leagues (e.g. the ABL and WNBA) are growing and multiplying. These factors also exert a strong "trickle down" effect, increasing the number of grade-school and high-school girls participating in sports, even in such previously male-dominated arenas such as football and wrestling.

This increased degree of participation has resulted in an epidemic of ACL injuries among women. Female athletes appear to have an ACL injury rate nearly twice as high as men (4.1 vs. 2.4 injuries per 1000 athletic exposures) During the U.S. Olympic basketball trials 13 out of the 16 ACL injuries occurred to women. Recently, the risk of injuring one's ACL during a collegiate basketball career was estimated to be roughly six times higher among women than men.

What's causing this increased injury rate? The bottom line is that we aren't certain. However, several theories have been proposed:

Theory 1- Despite the increased level of participation noted for women athletes, there are still fewer development leagues for young female players than for boys. Therefore, some female athletes may first try a particular sport when they are slightly older than a comparable population of boys. At that level of participation, a higher demand might be placed on the female knee, in conjunction with a lower overall skill level, or poorer conditioning, This may result in excessive force across the ACL, leading to tears.

Theory 2- The muscles surrounding the knee help to protect the ACL. Because of genetic and hormonal differences, women have less muscle mass (power) in general than men. In addition, some studies show they may use certain muscle groups around the knee differently, especially the hamstrings. These factors may result in deceased dynamic protection of the ACL during sports.

Theory 3- Females may, in general, have more joint laxity than males. This increased flexibility may lead to more ligament tears.

Theory 4- Due to a structurally-wider pelvis, women have, on the average, more of a "knock-knee" (valgus) alignment to their knees than men. In addition, this leads to higher degrees of rotation of the femur (thigh bone) during knee motion, which may place more mechanical stress on the female ACL

Theory 5- The ACL glides in the center of the knee, in the so called "femoral notch" during knee motion. Recent studies have noted this notch is narrower on average in women's knee, and have speculated that increased frictional, or other forces may excessively stress the ligament, leading to chronic wear and perhaps tears.

Theory 6- Recent studies have also shown that the ACL has estrogen specific hormonal "receptors" (sites hormonal action) within its substance. These studies postulate that these receptors may somehow allow the hormonal differences between men and women to affect ACL function and structural integrity. However, this work is presently highly speculative. We haven't seen a rash of ACL tears during a certain part of the menstrual cycle, for example.