How do young athletes get a meniscus tear?

Young athletes typically get a meniscal tear during a traumatic knee injury. The most common types of meniscal tears we see are actually in a middle age to elderly population and represent degenerative tearing where the tissue has gotten weaker and the injury may not be so significant that they know when it happened, whereas in a young athlete, it's typically a different scenario. "My knee felt normal until I did this on the soccer field, and now something isn't right. It's clicking, catching, popping. I've got swelling and pain in the knee. 

Young athletes represent a distinctly different entity where there's usually a very definitive mechanism, usually related to athletics or participation in sport, whereas middle age to elderly people don't tend to have that same mechanism of injury. Oftentimes they don't even know when it occurred. They just know the knee has started to hurt them over the course of several months. Same injury, but representative of two different subtypes of that injury.

Sports where you'd be more prone to a meniscal tear, particularly in a young population, are sports that involved heavy landing, twisting, and pivoting. Sports where we most commonly see it would be soccer, football, basketball. The types of sports where we're landing and twisting simultaneously are the ones where you have a much higher likelihood of a meniscal tear.