In 1998, the American Journal of Sports Medicine featured an article titled, “The Association Between the Menstrual Cycle and Anterior Cruciate Ligament Injuries in Female Athletes.” This article confirmed the suspicion that many coaches already had, which is that hormonal as well as anatomical predispositions were to blame for the seeming epidemic of female athlete ACL tears. I’ve come to the conclusion that there are three major reasons why women are more than four times more likely than men to tear their ACL’s playing sports (1).
In order to make hypotheses about women’s increased susceptibility to ACL tears, one must first understand the basic anatomy of the knee and the purpose of the ACL. First, the knee is a joint comprised of four bones—the femur, the tibia, the fibula, and the patella. The knee joint is padded by sections of cartilage (menisci) on both the medial and lateral side. The ACL is one of four major ligaments responsible for stability in the knee. The ACL originates in the notch of the distal portion of the femur and inserts into the tibia. Due to its origin and insertion, its primary purpose is to protect the knee from too much anterior translation of the tibia.
The first portion of the hypothesis we will discuss is the hormonal reason for women’s increased susceptibility to ACL tears. Dr. Kurt Spindle, an orthopedic surgeon in Nashville, has done some of the most relevant research on this portion of the female athlete’s epidemic. In his study, he discovered that women were three times more likely to tear the ACL when they were having their period. He explains this by stating that during a female’s period, the luteinizing and follicle stimulating hormones are allowed to enter the bloodstream. These hormones come into contact with the ACL’s recently discovered active hormone receptors. It is believed that this spike in hormonal levels can actually temporarily alter the composition of the ligament, therefore leaving the ACL more prone to tearing. Dr. Spindle also cited that women who had been taking oral contraceptives were less likely to tear their ACL. This is due to the fact that oral contraceptives skyrocket estrogen and progesterone levels, causing luteinizing and follicle stimulating hormones to not be released.
The second reason female athletes are at least four times as likely to tear their ACL is because of the difference in the anatomy of the hip. The term “q-angle” is defined as “a measurement of the angle between the quadriceps (rectus femoris is usually used) and the patella tendon (3).” Q-angles in women are generally at least five degrees larger than that in men, which causes an increased tension on almost all of the ligaments of the hip and knee. The hip structure that most women have is great for giving birth but not so great for playing sports requiring lots of multidirectional movement.
The third reason for female ACL tears is an anatomical predisposition. The intercondyler notch is a portion of the knee between the condyles that the ACL glides through during extension and flexion of the knee. These condyles are two rounded portions, one on each side of the notch. They provide a large source of stabilization for the knee. Think of the condyles as your knuckles when you put two fists (femur and tibia) together. One of the main purposes of the condyles is to give the ACL additional support by preventing too much anterior movement of the tibia. Women have smaller condyles (less knee stability) as well as a smaller intercondyler notch. The fact that women typically have smaller condyles is a distinct mechanical disadvantage that leaves women with less knee stability in general. Additionally, the smaller intercondyler notch that women have can lead to the ACL being pinched or torn inside the joint. So there are a host of anatomical differences in the knee joint of women that leave them more susceptible to ACL tears.
So what’s a girl to do? Should girls with wide hips avoid playing sports requiring multidirectional movements? Should girls sit out from playing sports when they’re having their period? Should collegiate athletic programs require their female athletes to be on oral contraceptives to lower their chances of season or career ending ACL tears? There are obvious legal and moral issues involved with asking female athletes to take oral contraceptives, but it’s an option I wouldn’t be surprised to see explored. However, my answer to this question is a resounding no. A study done by the American Journal of Sports Medicine declared that women who undergo lower extremities injury prevention workouts are 62 percent less likely to suffer traumatic knee injuries (5). This tells us that corrective/preventative exercises are definitely the way to go.
All three factors related to women’s relative knee instability are intertwined with the fact that women typically have roughly 30 percent less muscle mass than men. Muscle mass is one of the joints’ greatest stabilizers. There is a stigma in the exercise science field about training for larger muscles, but this stigma is largely unfounded. There is a belief that flexibility and muscle mass are mutually exclusive qualities. This isn’t true. Gratuitous amounts of muscle mass and flexibility, however, are mutually exclusive.
Flexibility is defined as “the ability of your joints to move throughout a full range of motion” (6). It’s discussed a lot in the athletic performance field, but sometimes we forget that being super flexible isn’t always good. Being too flexible can lead to joint instability because of the joints’ extremely large range of motion. This is why training for hypertrophy and balanced muscle ratios is so important. By training to achieve a proper quadriceps to hamstring strength ratio, female athletes can drastically decrease the likelihood of ACL tears (4). Most females, just like their male counterparts, are quadriceps dominant. Having strong quadriceps is great, but the hamstring complex by virtue of its origin and its insertion helps to prevent too much anterior translation of the tibia from occurring. This anterior translation of the tibia is the reason most tears of the ACL occur. This is why training your posterior kinetic chain, specifically your hamstrings, is so important.
Additional forms of corrective exercises should include multidirectional neural activation/enhancement drills. The quicker that muscles fire while an athlete is making a cut, the quicker the joint will be stabilized. Oftentimes ACL tears occur when an athlete plants a foot to cut and immediately the plant leg is compromised by a collision. It isn’t speculation to say that if surrounding musculature can fire quicker and stronger (more fibers), these plant and twist tears would become less likely.
In conclusion, it’s an undeniable fact that female athletes are up to four times more susceptible to ACL tears than their male counterparts. There are at least three scientifically proved reasons for this and perhaps more that we haven’t discovered. However, there is hope for the female athlete. There is a vaccine available to aid in putting an end to the “female athlete’s epidemic.” Through the combination of preventative exercises aimed at producing neural adaptation and balanced hypertrophy, there can be more healthy knees out there on the field of play.
1. Wojtys EM, Huston LJ, Lindenfeld TN, Hewett TE, Greenfield ML (1998) “Association between the menstrual cycle and anterior cruciate ligament injuries in female athletes.” The American Journal of Sports Medicine 26(5):614–19.
2. Spindler K (2002) “The Effect of the Menstrual Cycle on Anterior Cruciate Ligament Injuries in Women as Determined by Hormone Levels.” American Journal of Sports Medicine 30(2):182–88.
3. “The Q Angle.” The Virtual Sports Injury Clinic—Sports Injuries. Accessed: Nov. 12, 2009. At: http://www.sportsinjuryclinic.net/cybertherapist/front/knee/q-angle.php.
4. Pettineo, et. al. Female ACL Injury Prevention With a Functional Integration Exercise Model. Strength and Conditioning Journal 26(1):28–33.
5. Joseph M (2008) Knee Valgus During Drop Jumps in National Collegiate Athletic Association Division I Female Athletes: The Effect of a Medial Post. American Journal of Sports Medicine 36(2):285–89.
6. Marieb EN. (2008) Essentials of Human Anatomy & Physiology (9th Edition) (Essentials of Human Anatomy & Physiology (Marieb)). San Francisco: Benjamin Cummings.
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