The number of anterior cruciate ligament injuries in high-risk sports like basketball and soccer remains high, especially for women athletes. It has been estimated that one out of 10 collegiate women playing basketball will sustain an ACL injury during her college career.

Although 75 percent of ACL injuries are non-contact, the precise mechanism that results in an ACL injury is not clearly understood. Proposed risk factors for injury have included environmental, anatomic, hormonal and biomechanical factors. Although in the last several years there has been a fair amount of research attempting to relate hormonal levels (primarily estrogen and progesterone) to ACL injury, results have been conflicting. Similarly, since women have a greater rate of ACL injury than men do in certain high-risk sports, many feel those anatomic variables such as hip varus, knee valgus or foot pronation might be intimately linked to injury occurrence. However, no such relationship has been definitively shown in multiple studies looking for it.

Women more susceptible

In the late 1970s, the increased incidence of sport injuries in women appeared to be linked to inadequate conditioning or lack of playing experience; however, our collegiate women athletes are now well-conditioned athletes who are experienced in their sport. Then what is the answer? Why is the rate of ACL injury so high in our women athletes?

The late Chuck Henning, a well-known orthopedist in the Kansas City area, after reviewing numerous tapes of women athletes sustaining ACL injuries, attributed the increased rate of injury to what he termed the "quad-cruciate interaction." When the knee is extended, the quadriceps exerts a significant anterior translational force on the tibia, stressing the anterior cruciate ligament, the major restraining force to such translation. When the knee is bent, the quadriceps exerts less of anterior translational force on the tibia, stressing the ACL less.

Bending the hip and knees

To decrease the "quad-cruciate interaction" and hence decrease the risk of ACL injury, Henning felt that athletes should practice cutting, landing, and stopping with their knees and hips flexed. He instituted a program in the Kansas City area based upon this principle and reported a decrease in injury rates.

Recently, a group of researchers in Cincinnati led by biomechanist Timothy Hewett proposed adding to the normal preseason stretch and strengthening exercises plyometeric drills, emphasizing proper landing techniques with the hip and knee bent and the body balanced over the lower extremities. Analysis of injury rates in high-risk athletes participating in this program demonstrated a decrease in the rate of injury.

An ACL prevention program developed for downhill skiers by the Vermont Safety Research group emphasized increasing awareness of situations that can potentially result in an ACL injury and pre-planning strategies if events, leading to these situations, begin to fall into place.

Last year, the NCAA, concerned about the high rate of injury in collegiate athletes and realizing the significant physical and psychological consequences of this injury, helped sponsor the Hunt Valley Conference on ACL Prevention Strategies. This conference allowed orthopedists, biomechanics, family physicians, athletic trainers, and physical therapists to meet and review risk factors for ACL injury and the existing prevention programs. They concluded that even though the risk factors for injury have not been fully defined, early trials of existing prevention programs based on altering biomechanical risk factors appear to have had reasonable success in decreasing injury rates. Therefore, it seems appropriate to continue to pursue such programs while further defining risk factors for injury.

Since this conference, physicians, therapists and athletic trainers from the Santa Monica, California, area have, with the help of others, organized the first sports specific (soccer), on-the-field, ACL prevention program that easily can be incorporated into pregame and prepractice drills. This five-part program, called the PEP program, consists of avoiding vulnerable positions, increasing flexibility and strength while incorporating plyometrics, and increasing proprioception through agilities. It incorporates many ideas from the earlier prevention programs.