During the last decade, participation in women’s sports has grown immensely. Unfortunately, so has the number of serious knee ligament injuries sustained by female athletes.
Females are two to eight times more likely to rupture the anterior cruciate ligament (ACL) than males. Most are noncontact injuries, in which the athlete is either landing from a jump with an extended knee or quickly decelerating and pivoting. But it is important to analyze why female athletes are at greater risk: The anatomy of the femaleknee may contribute to the problem.
Within the joint, the ACL runs through a notch that is far narrower than seen in males. This is believed to increase the risk of its being pinched and torn during sports. The ACL itself is also smaller, which may predispose females to greater injury. Females generally have a wider pelvis, which affects lower-extremity knee alignment. This may lead to an unstable knee that can more easily buckle inward. Additionally, women tend to have more ligament laxity and increased muscle elasticity (flexibility). All of these elements make the female knee more susceptible to injury.
Another theory is that estrogen plays a role in injury and can diminish the tensile strength of the ACL and relax soft-tissue structures, placing the knee at greater risk.
Biomechanical factors have been the most revealing and helpful in developing ACL injury-prevention programs. Females tend to play sports standing in a more erect posture and typically land from a jump with straighter knees. Consequently, this amplifies the force through the joint and ACL.
There is also a significant disparity between hamstring and quad strength. Female athletes activate their hamstrings less and rely more on the quad for strength and power. A strong, overpowering quad coupled with a relatively straight knee position can lead to increased shearing on the ACL.
Neuromuscular timing issues of the leg muscles have been implicated in ACL injury. Research has shown that females demonstrate decreased muscle response times during jumping and cutting tasks compared to males. It is believed that a small delay is enough to disrupt the knee’s ability to adjust to a potentially injurious situation.
ACL injury-prevention programs show great promise. One important aspect of such a program is to train female athletes to rely more on the hamstring. Increased hamstring strength improves the ability to control dangerous forces. In addition, this muscle group is a dynamic stabilizer to the ACL and protects it from being overstressed. Ideally, the hamstrings should be 60 percent to 80 percent as strong as the quads.
An effective prevention program should incorporate balance-training activities that improve position awareness (proprioception). These tasks will help re-educate the leg muscles to sense potentially harmful positions and facilitate a faster protective reaction.
Plyometric, or agility, training is perhaps the most import aspect in the program. Plyometric activities focus on coordinated jumping, bounding, leaping, landing and cutting mechanics. Because most noncontact ACL injuries occur with the knee near full extension, athletes are taught to land softly with a flexed knee. Special attention is placed on increasing hip and knee flexion, limiting excessive side-to-side movement, inward buckling of the knee and leg rotation. These drills also improve reflexive and voluntary muscle response times.