? ? And next, here, tonight, everyone loves it when kids play sports. But are they risking something that could affect them the rest of their lives? Tonight, the injury epidemic to the knee that could... See More
? ? And next, here, tonight, everyone loves it when kids play sports. But are they risking something that could affect them the rest of their lives? Tonight, the injury epidemic to the knee that could lead to arthritis and other problems as they grow up. And ABC's chief medical editor, Dr. Richard Besser, has a solution. Reporter: Linsey vonn dropped out of the olympics. Tom Brady took a tremendous hit. Reporter: Tom Brady lost most of a season. It's an injury professional athletes fear, an acl tear. Now imagine that happening to your knee, in elementary school. When Caleb Seymour was just 7 years old, he took a bad hit playing tackle football. I went against the biggest, biggest person on the team. Reporter: Isabel loves gymnastics. But she blew out her knee at 9. Shocked. Reporter: She spent the last year in physical therapy, after acl surgery. We're seeing an epidemic. Almost weekly, a real young child coming in. Reporter: The main stabilizing ligament of the knee, is acl, isn't strong enough to take repeated movements by itself. Kids who play the same sport every day for hours, are at risk. And girls, six-times more likely to tear their acl than boys. There's a increased chance for arthritis later in life. Reporter: But new data says there's a simple solution. By doing them, you can reduce the risk by almost 75%. And a little athlete like Caleb Seymour, wouldn't tear his acl in the firth place. He wore Tom Brady's Jersey, number 12, to his year of rehab sessions. Then, we introduced him to his idol. Hi. How are you? You're Caleb? I'm Tom. Niced to meet you. How did you hurt your knee? Playing football. Playing football. It's a rough game. Guess who Elser to his knee. Me. Like any rehabilitation, you have to put your mind to it and hope it gets really strong. And rich is here now. Why are girls at greater risk? There's a few reasons. The shape of the hips is different. The muscles around the knee aren't as strong. And the ligaments are a little looser. But we know these exercises work. We have links to them on abcnews.com. Parents should ask their coaches, are they doing the exercises? And they're excellent for adults. Big prevention out there. Thank you, rich. When we come back here, the results are in. The American town where people
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