After undergoing surgery last summer for my second torn ACL in the past three years, I was inspired to seek out the answer to a question that is at the forefront of research in sports medicine. Why are female athletes more susceptible to ACL tears than their male counterparts? It is hard to deny that a rupture of the anterior cruciate ligament in the knee is an injury much more commonly seen in women than in men – females are anywhere from two to eight times more likely than males to tear their ACL. Sports with the highest incidence of ACL tears for females include basketball and soccer. The latter, a sport that involves twisting and quick changes of motion, is especially hard on the knees. According to some statistics, female soccer players are eight times more likely to tear their ACL than are male soccer players. Dr. Thomas Gill is Chief of Sports Medicine at Massachusetts General Hospital and Medical Director for the Red Sox and the Patriots. When I went in to see him in preparation for my second ACL surgery due to soccer injury, he told me that the most common re-tears he sees are in female soccer players. Collegiate athletes also seem to be particularly at-risk. While it is estimated that one out of 100 high school female athletes injure their ACL each year, for female collegiate athletes those odds are one out of 10. Furthermore, the NCAA approximates that in one year about 2,200 female collegiate athletes will tear their ACL.
There is no one universally accepted reason why women are more likely to sustain an ACL injury. Rather, it is likely a combination of factors that are responsible for putting female athletes more at-risk, including anatomy, muscle strength and usage, and leg position when landing a jump or performing cutting movements.
Differences in anatomy between males and females that lead to higher incidence of ACL tears among women include the size of the indercondylar notch and the Q angle. The ACL connects the femur and tibia and lies within what is called the indercondylar notch. The ACL moves within this notch, but its movement is restricted in women because they have a narrower notch. This restriction allows the thigh bones to pinch the ligament easily, especially during twisting or pivoting movements, and can ultimately lead to a tear. As for the Q angle, this is an angle that is formed where the femur meets the tibia. Pelvic size determines Q angle, and since females have a wider pelvis, their Q angle is larger. A larger Q angle means more force is concentrated on the ACL each time the knee rotates, increasing the risk of an ACL tear.
Females also tend to engage their ligaments and quad muscles more than males, which puts strain on the ACL. Men have greater muscle strength in the knee than do women, so women seem to rely more on ligaments like the ACL for stability rather than on muscles. Men also are known to have better quadriceps-hamstring balance. They engage the hamstrings first when performing a movement, which puts less strain on the ACL. Females’ quad and hamstring muscles may be more likely to cause the tibia to pull forward, putting the ACL at risk for strain.
Most of the ACL injuries in women, 93% of them, are non-contact and may be due to the tendency of females to perform planting, cutting and straight-knee landings with straight legs. Having this leg position during these movements could cause hyperextension of the knee, which leads to many non-contact ACL injuries. Women furthermore tend to turn their knees inward when jumping, pivoting or landing. Turning the knees inward could be due to females’ wider pelvis and greater flexibility, and it puts more strain on the ACL.
The good news is that many ACL injuries can be prevented if proper training and conditioning programs are followed. Neuromuscular and proprioceptive training of female athletes have been shown in studies to be successful at reducing the incidence of ACL tear. A study published in the American Journal of Sports Medicine claimed that a group of 366 female athletes who participated in a 6-week training program were 3 times less likely to tear their ACL than a group of 463 females who did not do the program, which included practicing jumping and landing techniques. The program, developed by Timothy Hewett and colleagues at the Cincinnati Sportsmedicine and Orthopaedic Center, also included stretching, weight lifting, and a focus on improving hamstring strength and overall agility. Plyometrics and agility drills, as well as hamstring-strengthening exercises, can indeed go a long way in helping to prevent an ACL tear. There continues to be ongoing research into the question of why females are more likely than male counterparts to tear their ACL. Understanding this discrepancy between the sexes is key to the development of successful training programs aimed at reducing rates of ACL tears in female athletes.
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