Knee injuries and women.

It has long been known that more sports-related injuries to the knee ligaments than men do. Injuries to the anterior cruciate ligament (ACL) are three to four times more likely among female athletes. Some sources say the difference is as high as six times. While sports like basketball and volleyball may place women at even higher risk, female runners also lead the pack in knee injuries.

Theories to explain this unfortunate fate have focused on bone structure differences between men and women. Studying the skeletons of 100 men and 100 women, researchers reporting at the annual meeting of the American College of Sports Medicine determined that the female knee has a smaller joint surface, which makes it more susceptible to injury. Other theories have focused on differences between hip width and angles and differences in conditioning. Understanding the underlying differences could help women train in ways that might offset their predisposition for these often devastating injuries.

A study reported at the Annual Meeting of the American Academy of Orthopaedic Surgeons suggested that women run and perform other athletic movements in a more upright position than their male counterparts (who as a rule move in a more crouched position). This research suggests that quadriceps strength dominates the hamstrings when running and moving in a more upright position. A deeper position (greater bend at the knees and hips) activates the hamstrings to a greater extent and provides more protection for the ACL.

Other experts believe that simple strength and conditioning differences between men and women is the best explanation for the high knee injury rate among females: men simply train for leg strength more over a longer period of time than women do.

In a recent laboratory experiment conducted to explain the higher rate of ACL injuries in women, researchers studied the effect of estrogen on ligament cells. The results showed that in the presence of--estrogen, ligament cells did not grow as well. The presence of estrogen receptors on ligament tissue has a biological purpose in enabling the pelvis to loosen adequately for childbirth. Instability of the knee may be an unwanted side effect of estrogen, and the findings could further explain the frequency of ACL injuries in women.

While research continues to explore the reasons for the different rates of injury, women can heed the message delivered by all of the studies. Active women should protect themselves with intelligent training aimed at balanced strength and flexibility. There is very little to argue against that wisdom.

(Clinical Orthopedics, 1999, Vol. 366, pp. 229-238; American Journal of Sports Medicine, 2000, Vol. 28, No. 1, pp. 131 and pp. 98-102; American Academy of Orthopaedic Surgeons, Press Release, February 1999 or go to www.americanrunning.org/webarticles/strengthtraining/strength.html)