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Oh, my aching knees. That's something us old people say, right? Increasingly, however, children are experiencing one of the most serious knee injuries out there – to the anterior cruciate ligament (ACL).

In a new clinical report from the American Academy of Pediatrics, a group of pediatric sports medicine experts outlines the current state of knowledge on the injury and its prevention.

The ACL is one of four ligaments that work to stabilize the knee joint. Among its many uses is protecting knees from the damage that can occur during athletic manoeuvres such as landing a jump, pivoting or decelerating from a run, says the report, which appears in the journal Pediatrics. During an injury, the ACL can tear, causing pain, a reduction in motion, difficulty bearing weight – often accompanied by a "pop," the authors write.

And while concussions have been a legitimate and very public cause of concern in kids' sports including hockey, football and soccer, this common knee injury has been on the rise over the last two decades in children under 18.

In addition to serious surgeries and long recovery times, which can affect a child's mental health and academic standing, one of the major concerns is that athletes with ACL injuries are up to 10 time more likely to develop degenerative arthritis of the knee. This can develop as early as 15 to 20 years after the injury, which means many kids will already be suffering in their 30s.

Why it happens: Most ACL injuries are sports-related and kids' participation in organized sports is on the rise. And kids are starting sports at ever-younger ages, explain the authors. They also admit there is a greater rate of diagnosis as a result of increased awareness about the injury. More specific risk factors, they write, include greater weight and body mass index (BMI) and physical characteristics such as "joint laxity," – which allows kids to hyper-extend their joints – and poor muscular control of the hip and knee. Previous injury is the "single best predictors of future ACL injury," according to the study.

What it looks like: Video analysis of competitive sports play has been helpful in showing what the injury may look like as it happens, write the authors. The hip is usually internally rotated, the knee is close to full extension, the foot is planted and the body is decelerating. "ACL injury is also observed to occur when the body's centre of mass is behind and away from the base of support or the area of foot-to-ground contact," they write.

Girls are more at risk: ACL injuries increase sharply after puberty for both genders, but girls are at more risk. "Adolescent females are more prone to ACL injuries than adolescent males playing similar sports – up to four to six times more likely to suffer an ACL injury," says report author Dr. Cynthia LaBella in a video press release. "And the research is showing that the primary reason for this is that girls simply use their muscles differently when they do athletic manoeuvres, compared to boys and that puts them at higher risk for tearing their ACL."

How to prevent it: The AAP recommends that young people who are playing sports at high risk for ACL injury – soccer, basketball and volleyball – participate in "neuromuscular training programs." These involve exercises to strengthen the key muscles that protect knees and learning skills such as how to land jumps safely.

Here in Canada, the Canadian Paediatric Society recently voiced its support of a Canadian injury prevention program called Playing Smart Soccer which was created by the Think First Foundation of Canada and the Canadian Soccer Association. The lead authors of the CPS paper on the program, pediatricians Kristin Houghton and John Philpott, recommended specific training programs:

"For teenagers, injury prevention programs such as PEP (Prevent Injury, Enhance Performance) and the FIFA 11 have been shown to reduce the incidence of this injury. These preventative programs focus on neuromuscular training, including strengthening and flexibility exercises, plyometrics [jump training], balance and technique training, and risk awareness."

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