Since Title IX was signed into law by President Nixon in 1972, a dramatically increasing number of female athletes participate in sports not only at the collegiate level, but also at the high school and recreational levels as well. Currently, there are just as many young girls playing competitive sports as boys.
Title IX made it illegal for any educational program or activity that received federal financial assistance to discriminate on the basis of sex or gender, giving females an equal opportunity to participate in organized athletics.
Unfortunately, with increased participation comes an increase in injuries. Specifically, recent studies have shown that female athletes are up to 8-10 times as likely to sustain devastating knee injuries, such as an Anterior Cruciate Ligament (ACL) tear, compared to their male counterparts. There are several theories as to why this may be the case, some of which may not be so obvious:
Evolutionarily, females tend to have wider pelvises compared to males for eventual child birth. This widening of the pelvis causes the knee alignment below it to be more “valgus” or knock-kneed. In addition, females are more likely to have rotational abnormalities of their femurs (thigh bones) and tibias (shin bones). During aggressive physical activities, these lower extremity limb alignment changes can place more force on the ACL than it can tolerate, making it susceptible to injury.
The major dynamic stabilizers of the knee during regular and aggressive physical activity are thequadriceps muscle group or thigh muscles. The particular muscles that athletes use to brace their knees when landing from a jump or hop are often weaker in females than in males, largely in part because of the differences in lower extremity alignment. In addition, the order in which the various quadriceps muscles fire or activate in female athletes is also different.
Fluctuating hormone levels—specifically estrogen and progesterone—in the female body can affect the biomechanics of the ACL tear. This can occur as a result of the menstrual cycle and exogenous hormone ingestion (birth control pills). Studies have shown that the strength of ligaments such as the ACL may be weakened by the presence of estrogen. In addition, other studies have suggested that ACL tears in female athletes are more likely in certain phases of the menstrual cycle.
The actual ligament itself tends to be slightly smaller and thinner in females. Also, the intercondylar notch, or space at the end of the femur (thigh bone) where the ACL is located tends to be narrower.
The combination of these factors coupled with increased aggression, physical activity and competition makes it apparent why female athletes are more susceptible to ACL tears. Unfortunately, most of these factors are inherent to being female and are not modifiable. Prevention programs are centered on increasing muscle tone, balance, improving muscle firing, as well as maintaining flexibility, core and overall strength.