Preventing Knee Injuries in Girls Playing Soccer

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Over the past twenty years there has been a substantial increase in girls playing in youth sports, especially soccer leagues. Although knee injuries occur at a high frequency with basketball, volleyball and soccer, this article will focus primarily on soccer related injuries.

Parents have become very familiar with the injuries associated with soccer and have noticed that lower extremity injuries are more common and that there are many more injuries associated with the women’s teams than the men’s, especially knee injuries. Although soccer has a low rate of injuries compared to other youth sports, current literature reports that the lower limb, specifically the ankle and knee, are the body parts most often injured in youth soccer.

Risk Factors

The anterior cruciate ligament (ACL) is one of the major stabilizing ligaments in the knee. Many ACL injuries in sports occur without physical contact with other players at the time of injury and are categorized as non-contact ACL injuries. It has been shown that a female athlete involved in cutting sports such as soccer, basketball and volleyball, is 4 to 8 times more likely to sustain a sports-related non-contact ACL injury than male athletes. Also, we know that the knee has a nearly six fold increased risk of re-injury with a previous injury to a knee and the ankle has a fourfold greater risk of re-injury if the athlete had a previous ankle injury. A prior injury is one of the single best predictors of future injury risk and ACL injuries to the opposite knee are even more common than re-injuries of the initial knee.

Why Girls Have More ACL Injuries Than Boys

Many factors have been explored to account for the difference between male and female athletes with respect to ACL injuries: ACL size; knee joint laxity; standing posture, foot pronation, also known as “dropped arch”, misalignment of the lower extremity, and pelvic position; and hormonal variations. Researchers have explored shoe-surface interaction; playing surface; skill level; level of conditioning, muscle strength, and altered neuromuscular controls. With regard to environmental, anatomical and hormonal risk factors, there is no conclusive evidence that any one single risk factor correlates directly with an increase in ACL injury in female athletes. Therefore, the emphasis has turned to body mechanics risk factors and the use of training and intervention programs to address potential body mechanics deficits.

Preventing ACL injuries is most important especially if you consider that ACL reconstruction surgeries are complicated for adolescents and often have poor results. Because of the concerns with surgical and nonsurgical treatments of ACL injuries in adolescents, ACL injuries are more devastating for adolescents than for adults, and the early training for prevention of noncontact ACL injuries in adolescents is important.

Inadequate Knee Control Causes ACL Injuries



Understanding injury mechanisms is a key component of prevention of non-contact ACL injuries. Mechanically, ACL injury occurs when an excessive tension force is applied on the ACL. A non-contact ACL injury occurs when a person themselves generates great forces at the knee that applies excessive loading on the ACL. This can occur in a number of ways: sudden deceleration, repeatedly performing landing and pivoting maneuvers, one-step stopping, cutting movements, sudden change of direction, landing from a jump with inadequate knee and hip flexion - at or near full extension, or a lapse of concentration resulting from an unanticipated change in the direction of play.

ACL injuries typically occur immediately after landing during a deceleration maneuver combined with a change of direction while the foot is planted on the ground, also called a closed-chain position. While the foot is planted and pronated (rolled in), the tibia of the lower leg is turned inwards, and the knee is nearly straight or near full extension. If the athlete attempts to change direction, the result is an excessive twisting force that can potentially strain or rupture the ACL.

A study of children 5 to 12 years of age in youth soccer demonstrated that there is no gender difference in knee injury risk before puberty in athletes. With athletes over 11 years of age there was a significant risk factor for knee injury in girls. Compared to their male counterparts, changes that occur in the female athlete while performing a stop-jump task include: decreased knee and hip flexion angles at initial contact, a tendency to land with the lower extremities more extended, and they maintained knee valgus (varus is “bow legged” and valgus is “knock-kneed”) at initial foot contact with the ground. The degree of these changes increased with age. Research studies indicate that the ACL injury rate in adolescents increases linearly after 12 years of age and that adolescents at 17 and 18 years of age have the highest ACL injury rate.

A lead investigator in a comprehensive study, Timothy Hewett, PhD, director of The Sports Medicine Biodynamics Center and The Human Performance Laboratory of Cincinnati Children’s Hospital and University of Cincinnati College of Medicine, “The most important finding in this study is that growth in height and bone length without increased strength and power in girls appears to be related to decreased control of the knee and potentially, increased injury risk.”

Training for Prevention Also Helps Performance

A comprehensive training program can lead to improvements in athletic performance and movement biomechanics as well as reduce ACL injury risk in female athletes. Improving technique should be the emphasis of training: landing softly, increase knee flexion, minimize knee valgus (align the center of knee cap with the first toe). Improving running technique to include accelerated rounded turns, decelerate with a multi-step stop, and maintain proper knee alignment and knee flexion during cutting maneuvers. Strength conditioning should focus on increasing hamstring, gluteus maximus, gluteus medius (hip extension and abduction) strength and reactivity. It is important to note that long duration or repetitive exercises may actually increase the chance of injury as the athlete will become fatigued and fail to employ proper form. Warming up properly is important before training for any sport, but especially for the female athlete. Lunges are also once of the worse exercises to perform for more than 1 minute.

An excellent resource for a training program can be found at Santa Monica ACL Injury Prevention Project or PEP for short. Consult with your coach or club board members to bring in a qualified trainer to go over an ACL strengthening program. Many colleges and universities have outreach programs where they will come out to your youth training facility and meet with your coaches and training staff.