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Orthopedists slowly gaining insight into ACL injury risks
Research has shed light on injury mechanisms and yields new intervention and prevention techniques.
Sports medicine specialists are working to identify various risk factors and to devise techniques to reduce ACL injuries. Keen assessment and rigorous training are proving essential to minimizing this common athletic injury.
Orthopedics Today asked three experts to discuss recent advances in identifying and assessing ACL injury risk — Elizabeth A. Arendt, MD, University of Minnesota; John A. Bergfeld, MD, Cleveland Clinic; and Timothy Hewett, PhD, Cincinnati Children’s Hospital Medical Center. Arendt and Bergfeld are members of the Orthopedics Today Editorial Board.
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![Elizabeth A. Arendt, MD [photo]](images/content/OT/200608/arendt.jpg)
“I think we’re making progress,” Bergfeld said. “We’re beginning to get some validated data other than just opinion. The postulate was the mechanism of injury in females having quadriceps-dominant knees and their mechanism of landing from a jump being different than the males. There were some early clinical studies done. They were OK,” but some of what the authors presented was based on opinion.
Bergfeld said research by colleague Scott McLean, PhD, and Hewett on training and injury prevention broke new ground.
“There are a couple of laboratories [that are] looking at this a little more closely,” Bergfeld said. “It’s still early, but it’s looking like their postulate may be true, that by educating the females and putting them on a training program, we can reduce the incidence of ACL injury.”
Overall, females have a higher incidence of ACL tears than males, Arendt said.
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![John A. Bergfeld, MD [photo]](images/content/OT/200608/bergfeld.jpg)
Noncontact injury mechanisms are common among both males and females, but females suffer a higher percentage of noncontact ACL tears. In contrast, males sustain a higher percentage of contact-related tears because more males play contact sports, especially football, she said.
Neuromuscular “spurt”
Boys, unlike girls, experience a natural neuromuscular “spurt” during puberty, Hewett said. However, training can trigger the same effects in girls.
“You can get changes over relatively short periods of time [with females],” he noted. “In a couple months of training, you can get a drop in the amount of valgus collapse of about 50%. You can increase their vertical jump height 10% to 15%. You can make them more powerful, and you can give them better neural control over their knee.”
Females tend to be “ligament dominant,” relying on the ligaments, rather than the larger muscles to absorb force, he told Orthopedics Today.
They also tend to be “quadriceps dominant,” under-using the flexors around the knee, which absorb force and protect the ACL. Many females are also “side-dominant,” loading one side more than the other, he added.
Training can help females avoid valgus collapse, strengthen their hamstrings and balance their hamstrings side to side, thus reducing the injury risk, Hewett said.
Meanwhile, researchers who explored the role of balance in ACL injury reported a high injury risk for males, Hewett pointed out.
“Basically, what it boils down to is that females are better single-leg balancers than males,” he said. “That’s why in gymnastics, the females are on the balance beam and the men are on the rings. Improving that across the board in all females didn’t have a significant effect on reducing their injury rate, though we do think it’s a useful adjunct when you combine it with plyometrics and technique training.”
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Images: Hewett T |
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Mechanisms/prevention
Current research focuses on neuromuscular coordination relating to specific maneuvers, particularly the plant-and-pivot, start-and-stop and jump landing moves, Arendt told Orthopedics Today.
For example, the jump maneuver involves a soft landing with a bent knee and hip, allowing the lower leg muscles and ligaments to absorb landing forces more safely. In the plant-and-pivot maneuver, the athlete is taught to keep his or her leg in a “cylinder” shape over the knee to maintain balance and control body weight, Arendt said.
“All of these maneuvers that we’re learning about and then teaching … the goal of them is to try to control the rotation of the limb under the body,” she said.
Specialists have various tools, like videos, to identify injury mechanisms, but Arendt cited new identification strategies, such as analysis of 3-D motion and electromyography recordings, as promising new measurement instruments.
“I think we’re getting closer to [understanding injury mechanisms], but once you have an injury mechanism identified, you’ve got to figure out how to prevent it,” Arendt said. “That’s where the intervention techniques have come in. Then, the question is, ‘How successful are we at trying to reduce injury?’ It appears on the surface that we have been reasonably successful in reducing injury.”
Retaining information
Also, little is known about the extent to which athletes regress or forget prevention techniques and require re-training, Arendt said.
“Do you learn it once and then store it in your neuromuscular memory?” she said. “Does the age of learning these maneuvers matter? These are the questions that need to be answered to best apply any intervention program to the greater population at risk.”
Multiple factors contribute to ACL injuries, and more research is needed to link certain risk factors to specific ACL injuries, Arendt added. Although researchers have struggled to make these links, they are starting to make some progress.
“We certainly are closer, much closer, to understanding this, but it is much more involved and complicated than I ever imagined,” Arendt said. “It is an extremely large project.”