Interesting, I had this same condition as a teenager. The name "Osgood-Schlatter's Disease" sounds like something extremely scary but it's very minor. As far as I can remember from my doctor and researching it at the time, it's caused by the tendon in your knee pulling on the top of your shin and it's most common in teenagers who play sports because your muscles develop more quickly than your bones and are disproportionately strong relative to your still growing bones, so the tendon is pulling harder on your shin bone than it "should". It's not a long term structural thing at all and isn't specifically a "knee" problem with the joint itself, and it just goes away with time as your bones finish growing.
For me it stuck around periodically from about age 17-19 and I'd have pain below my knee (mostly my left knee) after playing hockey. Otherwise I never had any issues with it from playing football or doing any other exercise, just some minor pain after hockey games & practices that was easily resolved with ice & advil (usually didn't need to do anything) and then it just went away once I got into my 20s.