MRI Measures Knee Geometry and Its Role in Severe Knee Injuries

Researchers are examining multiple factors such as the size of the knee’s femoral notch to attempt and clarify why some people are at greater risk for injury than others.

The moving of an athlete’s body relies on a coordinated response of joints, ligaments, bones, and tendons, putting the geometry of a key part like a knee joint to the test. However, it is more than just a footfall mistake at the root cause of one of the most devastating of sports injuries: the anterior cruciate ligament (ACL) tear. In reality, size—of the femoral notch that is situated at the center of the knee joint—and volume of the ACL combine to influence the risk of suffering a noncontact ACL injury. Additional geometric characteristics of the knee, such as the slope of the articular surfaces, are involved with risk of injury.

Several recent studies—including a highly-controlled study of first-time ACL injuries in Vermont high school and college athletic team members—conducted by University of Vermont (UVM; Burlington, USA) professor of musculoskeletal research Bruce Beynnon, PhD, and colleagues. With only 200,000 to 300,000 injuries yearly, ACL injuries are far less common than ankle ligament injuries, which number more than two million injuries in the United States alone yearly. However, ACL injuries can end sports careers and are proven to lead to the early onset of osteoarthritis.

“It’s a concern because its highly likely that an individual that suffers this injury will progress to end-stage arthritis in 15 years and the only solution at that point in time—knee joint replacement—only lasts about 15 to 20 years in an active individual,” explained Prof. Beynnon.

While the rate of ACL injuries across the United States have not changed over time, according to Prof. Beynnon, he and his team have looked at and continue to research the many variables at play when this injury takes place. In the study, published August 2014 in the American Journal of Sports Medicine, he and colleagues have “very accurately characterized the incidence rate and magnitude of this problem in Vermont,” stated Prof. Beynnon.

The researchers examined 88 student athletes—27 male and 61 female—who suffered first-time, noncontact ACL injuries during the study and compared their measurements—collected using magnetic resonance imaging (MRI) images of their knees—to a non-injured control group of 88 athletes (same male-female breakdown) from the same teams, with the same extrinsic factors, like environment, playing surface, training, footwear, level of competition, and coaching.

These measurements led them to look at the point where the ACL is positioned in the center of the knee—the femoral notch—where they measured its width, as well as ACL volume utilizing MRI technology in the University of Vermont’s MRI Center for Biomedical Imaging. One of the findings they discovered is that the risk of injury increased as the size of the femoral notch and ACL decreases.

“Prognostic studies are designed to identify who is likely to suffer injury so we can target injury prevention programs at them, and determine why they are at increased risk so we can inform the development of the programs to reduce the risk of injury and re-injuries of the same kind,” noted Dr. Beynnon.

In a parallel five-year epidemiologic study, also published in the August 2014 American Journal of Sports Medicine, the researchers reported on “The Effects of Level of Competition, Sport, and Sex on the Incidence of First-Time Noncontact Anterior Cruciate Ligament Injury.”

From the data gathered from a total of 38 institutions located throughout the US state of Vermont, colleges reported 48 ACL injuries during the sport seasons studied, while high schools reported 53 injuries. The researchers learned that college athletes had a significantly higher ACL injury risk than high school athletes—approximately two-fold—and that female athletes were two times more at risk for ACL injuries than males. In comparison to athletes taking part in Lacrosse, risk of ACL injury was substantially greater among those participating in soccer and rugby.

In their conclusion, the study’s authors stated, “An athlete’s risk of having a first-time noncontact ACL injury is independently influenced by level of competition, the participant’s sex, and type of sport they participate in, and there are no interactions between their effects. Female college athletes have the highest risk of having a first-time noncontact ACL injury among the groups studied. The first step is to establish the athletes most at risk; targeting interventions comes second.”

The investigators are currently conducting a multivariable study that has 109 participants. They are examining the role of a range of diverse factors to try to additionally identify those at increased risk for ACL injury. “It’s not just biomechanics, it’s biomechanics and biology,” Prof. Beynnon stated, adding that family history—a genetic link—could be the driver of such variables as problems with ACL collagen synthesis and degradation, joint laxity, exercise and diet, body mass index, and an individual’s inflammatory response.

Prof. Beynnon hopes, in five to 10 years, his group can repeat their epidemiologic study to validate their findings, evaluate the high school and college athlete model on a different, independent sample of individuals, and is considering developing an intervention study. “Primary prevention is the ultimate goal,” he said. “We want to reduce the risk of injury and burden of disease for this young age group.”

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