More Accessible Screening Can Reduce ACL Injuries in Female Athletes
Female athletes are two to six times more likely to sustain an anterior cruciate ligament (ACL) injury than males. Now, identifying teenage female athletes at greatest risk of an ACL injury could become easier, according to a new study from Sports Medicine at Cincinnati Children's. Once identified, these young women can undergo targeted neuromuscular training to lessen the likelihood of injury.
"We developed simple measures so that pediatricians can take a portable lab into the community when they conduct sports pre-participation physicals. Using a camcorder and portable force plates in a gym, pediatricians can reproduce the screening results we've documented in our lab," explains Timothy Hewett, PhD, director of Sports Medicine and the study's lead author. A force plate measures forces of stepping, jumping and other human-scale actions.
The pediatrician or other professional conducting sports physicals can use a camcorder to observe and record the amount of "knee collapse" as each student drops off a one-foot-high box onto the force plate and immediately jumps as high as possible. Examiners also can assess relative hamstring strength and side-to-side balance. An imbalance revealed in any of these three tests indicates the athlete may be at greater risk for an ACL injury and should undergo training to decrease that risk.
Dr. Timothy Hewett is shown here observing an athlete jumping from a force plate, one of several technologies designed to screen for athletes at higher risk for ACL injuries.
Female Risk Factors
This study of 275 middle and high school athletes in Texas confirmed and extended Dr. Hewett's earlier findings of male and female differences that may contribute to increased ACL injuries in females. During puberty, males experience a neuromuscular growth spurt that increases their jumping power and decreases their risk of ACL injury. Females, however, do not experience similar growth. As a result, their risk of ACL injury remains the same or worsens.
Three neuromuscular imbalances that stress leg joints, particularly the knee, are seen more in female athletes than in males. Ligament dominance causes ligaments rather than muscles to absorb force. Quadriceps dominance is an imbalance between knee extensor and flexor strength. With leg dominance, one leg is much stronger or more coordinated than the other.
Training that Works
For high-risk athletes, a combination of screening and training could help to identify and prevent the estimated 40,000 knee injuries a year in female high school and collegiate athletes. "Most young ladies don't even know that their body positioning is putting them at risk," Dr. Hewett says. He and his team have developed training to improve strength, coordination and balance and thereby reduce the risk of ACL injury. Training usually occurs two to three times a week in half-hour to hour-long sessions over six to eight weeks. The team from Cincinnati Children's has set up programs for schools and teams across the country and around the world.
"Most girls start from a low baseline and see significant improvement. It's very rewarding, because the girls, their parents and their coaches see results. This training develops not only a potentially safer athlete, but also a better athlete," Dr. Hewett explains. He is the lead author in a recently published book, Understanding and Preventing Noncontact ACL Injuries, aimed at helping coaches, trainers and medical professionals improve outcomes for athletes.
"ACL injuries are greater than a $1 billion problem for the United States, and a $625 million problem in women's varsity sports alone," Dr. Hewett says. "Twenty years after their injury and despite surgery, many of these women need medications or knee replacements to control knee pain. That's why the study of why and how females injure the ACL – and how we can prevent those injuries – is so important."
Timothy Hewett, PhD, is research associate professor and director of Sports Medicine at Cincinnati Children's. This study appeared in Clinical Journal of Sports Medicine (2006;16[4]:298-304).
