The chances of an ACL (anterior cruciate ligament) injury is about a five times greater for a female athlete than for a male athlete. ACL injuries are common in women’s sports of soccer, basketball and volleyball. Untreated, ACL injuries result in an unstable knee. This is unsuitable for sports and if left uncorrected can lead to damage of the joint and secondary arthritis. When treated surgically, ACL injuries result in long recovery periods of rehabilitation and absence from sport. ACL injuries in the United States account for about one billion dollars in medical costs. The ultimate goal is to prevent this injury if possible. To understand how to protect the ACL ligament we need to understand the conditions that often lead to ACL injury. Significantly, most ACL injuries in females do not involve contact with another player. (1) Biomechanics of muscle movements and joint positioning are different for females in several key areas and these play a key role in leading to injury. These biomechanical differences influence how the female athlete jumps and how she makes a side-step cuts. These two factors place her at increased risk of ACL injury. (2)
A female athlete is especially vulnerable to ACL injury when she lands after jumping. If she lands relatively straight-legged with extended hips, extended knees, onto flat feet, the ACL is placed at risk of injury. In addition, recent studies show that maintaining a knock-kneed (valgus) position when pushing off to change direction during a sidestep cutting maneuver is another likely injury mechanism. (3)
There are additional factors implicated in ACL injury such as the amount and timing of the force generated by the quadriceps muscles and hamstring muscles. Physiologic studies using EMG (electromyography) show that male and female athletes differ in this regard. To an extent, this derives from anatomical differences between males and females. We know that females have relatively less muscle strength in the hamstring and quadriceps and wider hips than males. Wider hips and weaker leg muscles make it somewhat more likely for a female to place her knee in the valgus position as well as use her knee in a more extended position. The bottom line is that an untrained or improperly trained female athlete naturally tends to jump and land in a more straight legged body position and she changes direction when running with her knees more knock-kneed (valgus) than her male counterpart. When jumping in this position, the female athlete lands hard, on flat feet, with little cushion. With little knee bend the ACL is already in a position where it is loaded stabilizing the knee. (4) Combine this with a harder landing and the ACL is subjected to forces which it may not be capable of withstanding. In the other mechanism of injury the female athlete tends to change running direction, or sidestep cuts, by placing the outside knee in a valgus or bent inward position. This is demonstrated in the following pictures on the GirlsCanJump.com website: http://www.girlscanjump.com/training-library.html.With the knee in valgus there are greater forces placed on the ACL than if the knee is directly over the foot or even in a slightly varus bowlegged (varus) position. (3)
Can the incidence of ACL injuries in female athletes be reduced and if so, how? Hip width cannot be changed. Muscle strength to some degree can be increased. Most importantly, what must be changed to avoid injury is the pattern of muscle movement. Female athletes can change the way they jump, land, and pivot to reduce the forces these movements place on the ACL. Studies done by the Santa Clara Orthopedic and Sports Medicine group have proven that ACL injury can be reduced by retraining body mechanics using new and improved training methods. This training changes the way the female runs and jumps so that "muscle memory" and motor strength of certain muscle groups protect the knee and prevent the female athlete from placing her knee in positions of vulnerability during sport. Simply stated, we have to teach our girls to run, cut and jump like boys to avoid this injury.
The Santa Monica Orthopedic and Sports Medicine Group, http://www.aclprevent.com/ has studied injuries in thousands of female athletes over several years. The group has applied this knowledge to develop an injury prevention training program designed to reduce the incidence of ACL injuries in female athletes. As a result of the exercise program, the group has been able to reduce ACL injuries in female athletes who participated in the program by three-fold. The program is known as the PEP (Prevention and Enhanced Performance) program and it is a series of exercises that replaces the traditional warm up and stretch. The virtual classroom demonstrating these exercises can be found at http://www.aafla.org/3ce/acl_frmst.htm. Their purpose is to change muscle movement patterns and enhance strength in certain muscle groups. The ultimate goal is to train the female athlete to avoid the positions of biomechanical vulnerability that lead to ACL injury. (2)
By incorporating the principles of the PEP training coaches, trainers, physical therapists and doctors can keep our female athletes out on the field having fun and staying safe.
I would like to extend special thanks to Bruce Snell and Dave Andrews of NW Sports and Physical Therapy, Gig Harbor and Tacoma Washington for their community lecture series. Their presentation of this materiel spurred my interest in this topic. I want to thank them in promoting preventative health of our young athletes of all sports.
References:
Griffin LY, Agel J, Albohm MJ, Arendt EA, Dick RW, Garrett WE, Garrick JG, Hewett TE, Huston L, Ireland ML, Johnson RJ, Kibler WB, Lephart S, Lewis JL, Lindenfeld TN, Mandelbaum BR, Marchak P, Teitz CC, Wojtys EM., J Am Acad Orthop Surg. 2000 May-Jun;8(3):141-50.
Malinzak RA, Colby SM, Kirkendall DT, Yu B, Garrett WE., Clin Biomech (Bristol, Avon). 2001 Jun;16(5):438-45.
McLean SG, Huang X, Su A, Van Den Bogert AJ., Clin Biomech (Bristol, Avon). 2004 Oct;19(8):828-38.
Howe JG, Wertheimer C, Johnson RJ, Nichols CE, Pope MH,Beynnon B., Arthroscopy. 1990;6(3):198-204.
