Pig Knees and Rising Youth ACL Tears

Over the last two decades, kids between the ages of 6 and 18 have seen a rise in ACL tears.

Anterior Cruciate Ligament (ACL) tears are on the rise, particularly among the young. That’s according to research in the official journal of the American Academy of Pediatrics.1

Anterior Cruciate Ligament (ACL) tears are on the rise, particularly among the young. That’s according to research in the official journal of the American Academy of Pediatrics.1

From 1994 to 2013, the researchers found a 2.3% increase annually in the number of ACL tears in patients between the ages of 6 and 18. It was also found that females had a higher rate of injury by a significant amount for younger age groups, while males between 17 and 18 years old were most frequently afflicted.

The researchers didn’t look at the whys of this increase over a 20 year period, but some of the likely reasons could be the increase in intensity, frequency, and force of sports for kids. It could also be that kids are forced into excelling at one sport without any overall conditioning and training to develop different muscle groups, meaning fatigue and an increase likelihood of injury. All typical reasons that apply to older, as well as younger, athletes.

So it’s good news that researchers from North Carolina State University and the University of North Carolina at Chapel Hill have published research2 on how the knees of pigs compare to human knees at various stages of maturity. Their findings will advance research by this group and others on injury treatment in young people.

“There’s a lot we still don’t know about how human knees work at different stages of maturity,” says Matthew Fisher, corresponding author of a paper on the research.

“What we’ve developed is a model that will allow us—or any research team—to study changes in the knee joint using pig knees,” says Fisher, who is an assistant professor in the Joint Department of Biomedical Engineering at NC State and UNC.

“Our ultimate goal is to improve clinical treatment of joint injuries in children and teens, given the increased participation in sports and rise of injuries, such as to the anterior cruciate ligament or ACL,” Fisher says. “We’re specifically focused on changes that take place during the growth process, such as changes in the placement and orientation of ligaments during growth.”

Previous research had established that adult pig knees serve as a good model for research into adult human knees. However, less was known about how comparable pig and human knees were at various stages of growth.

For this study, researchers examined pig knees at six stages of growth, between birth and 18 months, which is comparable to early adulthood in humans. The researchers then compared the growth stages found in pigs to the available data on human knee growth.

“We focused on how the orientation of knee ligaments changes over time,” says Stephanie Cone, lead author of the paper and a Ph.D. student in the Joint Department of Biomedical Engineering. “And we found that the transitions in ligament orientation we saw in pig knees at various stages of maturity mapped very closely to the existing research on humans at comparable stages of maturity.”

“We’re excited about the potential for this model, but tracking ligament orientation using MRIs is really only a starting point,” Fisher says. “Our next steps include testing the pig knees mechanically, in order to help us better understand how they move at various stages of growth: which joint components bear load, how these elements interact, and so on. A number of things change as we mature, but we are still trying to clarify the details, and those details can eventually inform future clinical practice. In fact, surgeons can use the pig model to test new surgical approaches for children and adolescents.”

In the meantime, it is unlikely that in a highly competitive environment, we’re going to see major changes to student athletes’ training programs without a significant change in attitude among educators and coaches. While it may seem that the solutions are obvious, the reality is that kids are not getting the best coaching, while they are still expected to perform at the highest levels for their age.

1. Beck, Nicholas A., J. Todd R. Lawrence, James D. Nordin, Terese A. DeFor, and Marc Tompkins. “ACL Tears in School-Aged Children and Adolescents Over 20 Years.Pediatrics 139, no. 3 (March 1, 2017): e20161877. doi:10.1542/peds.2016-1877.
2. Cone, Stephanie G., Sean G. Simpson, Jorge A. Piedrahita, Lynn A. Fordham, Jeffrey T. Spang, and Matthew B. Fisher. “Orientation Changes in the Cruciate Ligaments of the Knee during Skeletal Growth: A Porcine Model.Journal of Orthopaedic Research, May 4, 2017. doi:10.1002/jor.23594.