Answered by Diane Hillard-Sembell, MD Medical Director of AthletiCare.
Injury to the anterior cruciate ligament (ACL) in the knee is a common sports injury often requiring surgical reconstruction and several months of rehabilitation. The ACL is one of two ligaments that cross in the center of the knee joint. It connects the femur to the tibia and lends stability to the knee.
Females involved in cutting and jumping sports are four to eight times more likely to tear their ACL compared to their male counterparts in similar sports. There are many theories as to why females tear their ACL at a higher rate than males. The female anatomy, with its wider pelvic bone, causes a more exaggerated angle from the hip to the knee resulting in a more "knock-knee" or valgus landing position. The size of the notch in the bone in the knee where the ACL passes is also smaller in women. Hormonal fluctuations may have an effect on ligament tightening and loosening, but research at this stage is contradictory. The most important difference, and the one factor which can be modified, is that females simply move differently than males.
Women tend to fire their quadriceps more to stabilize their knees, causing them to hit the ground with a straighter leg putting more stress on the ligament. In contrast, men fire their hamstrings more, which allows them to land in a more flexed knee position and lessen the strain on the ligament.
Females also tend to favor one leg over the other. This leads to muscular imbalances that also put the ligament at greater risk. And, jumpers who land with their knees in a valgus position greatly increase their risk of injury by placing abnormally increased loads on the ACL. AthletiCare recently completed a 4-year research study entitled, "ACL Injury Risk Factors in the High School Athlete." This study evaluated nearly 500 athletes at 23 local high schools. It analyzed multiple anatomic measures, as well as jumping and landing mechanics.
Results agree with other published studies documenting an imbalance of strength between hamstrings and quadriceps in female athletes (female hamstrings are relatively weaker). In addition, females exhibit weaker hip musculature in relation to body weight, which may be a factor in poor landing mechanics. This research also identified peak injury rates and strength deficits in the freshman and sophomore group, making a case for prevention programs to be implemented early.
Preventative programs can correct the neuromuscular imbalances of female athletes and train them in proper jumping and landing techniques. These programs use a combination of strengthening, jump training, plyometrics, balance, core stabilization and flexibility. Have a questions for AthletiCare? Email us.
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