Researchers have several theories regarding the specific factors behind a female's increased risk, but these theories are still just that -- theories. Despite not knowing exactly what causes women to suffer more ACL injuries, many women's sports programs have implemented ACL injury prevention programs for their female athletes. So far, these prevention programs have been showing positive results and appear to help the athletes reduce their risk of a variety of knee injuries.
What Causes an ACL Injury?ACL injuries are common in sports that involve sudden changes of direction, such as football and soccer. Most knee injuries aren't caused by direct trauma or contact; they occur during a sudden twisting motion, such as when an athlete's feet are firmly planted and the knee and torso suddenly twist in the opposite direction. This often happens when landing from a jump, pivoting or missing a step.
Why Do Women Have a Higher Risk of ACL Injury?Researchers who have conducted studies on factors leading to ACL injury in female athletes have proposed several theories as to the reason women sustain nearly ten times the number of ACL injuries as male athletes. The top theories include the following:
- The Q-angle
The most obvious anatomic difference between men and women that may lead to ACL injuries is a wider pelvis in women then men. This difference results in a wider "Q-angle," or quadriceps angle. This is the angle at which the femur (upper leg bone) meets the tibia (lower leg bone). It is thought that this increased angle places more stress on a woman's knee joint, which makes it less stable than a man's knee joint.
- Anatomy of the Knee Joint
Women tend to have much smaller surface areas in the knee joint, including the two rounded ends of the thigh bone called the femoral condyles. The space between these condyles, the femoral notch, is the space in which the ACL connects the femur to the tibia. Some researchers speculate that the small space of a women's femoral notch may be more likely to cause impingement of the ligament and ultimately result in an ACL tear.
- Biomechanics and Movement Patterns
Studies have repeatedly shown that, in general, women have much different movement patterns in the knee joint than men. When landing from jumps, squatting and pivoting, women tend to role the knee inward slightly and pronate the foot, which may also lead to an ACL injury.
- Neuromuscular Factors
Some research findings have show a marked difference in neuromuscular control in women when landing jumps. These studies indicate that the average female athletes has less hip and knee flexion than the average male athlete, which may result in higher stress or strain on the ACL.
- Muscular Fatigue
Another theory sometimes mentioned includes muscular fatigue and ligament strength. While fatigue can affect anyone, some feel that women are more likely to suffer muscle fatigue sooner than men. When the muscles that stabilize the knee fatigue, the tension and force of movement is transferred to the ligaments. Because the ligaments of women tend to be smaller and weaker compared with a man's, women are more prone to a higher rate of ligament injury.
The data linking hormonal differences between men and women is not consistent, but there is a theory that different concentrations of estrogen and progesterone could affect ligament strength and stiffness, which has an impact on ligament injuries in women. Much more research needs to be done to say this with any certainty.
Despite these theories, we can't say with certainty what is behind the increased risk of ACL tears in women. It may be a combination of these things, or something not yet identified.ACL prevention programs have been shown to reduce the risk of ACL injuries in women athletes. Such programs include training drills that require balance, power and agility. Plyometric exercises, including jumping and balance drills, help improve a women's neuromuscular conditioning and muscular reaction. These factors have been shown to reduce a women's risk of ACL injury to the same level as a man's.
The bottom line for both men and women who participate in start and stop and field sports is to practice appropriate skills training in order to avoid injuries, including ACL tears.
American Academy of Orthopaedic Surgeons, Three studies examine causes, prevention of ACL injuries in women, News Item, February 26, 2005.
Griffin LY, et al. "Noncontact Anterior Cruciate Ligament Injuries: Risk Factors and Prevention Strategies" J. Am. Acad. Ortho. Surg., May/June 2000; 8: 141 - 150.
Hewett TE, et al. "The effect of neuromuscular training on the incidence of knee injury in female athletes: A prospective study." Am J Sports Med 1999;27:699–706.
Santa Monica Orthopaedic and Sports Medicine Research Foundation, ACL Injury Prevention Project.
Slauterbeck J, et al. "ACL injuries in women: Why the gender disparity and how do we reduce it?" Orthopaedics Today 23:1, July 2003.