Twelve year old Katie Foster has been practicing gymnastics since she was 2 years old.
She loves to tumble and fly through the air.
"When you twist in the air it feels good," she says.
But about a month ago, her favorite flips and jumps started to cause her pain.
At first the pain scared this Olympic hopeful because she didn't know what it was.
"Before I found out I had Osgood Schlatter's she broke her knee and she said it kind of felt like that when it broke and I was like, oh no I hope I didn't break it," Katie said.
Her pain was right below her knee though, and that tipped her doctor off that it was Osgood Schlatter's.
Dr. Allan Preddy explains what Osgood Schlatter's is all about.
"As the femur grows, the long leg bone grows rapidly. And in adolescents that causes the quadriceps or the big muscle in the frontal leg to grow rapidly. Sometimes it doesn't keep up with the leg, so it puts a lot of force where it hooks into the bone in the front of the knee. And with a little too much force it tears a bit of the bone and that's where the inflammation comes from. That's basically what Osgood Schlatter's is, inflammation."
Fortunately for Katie, this isn't particularly harmful and most teens do grow out of it. But Osgood Schlatter's is painful.
So Dr. Preddy gave her some pain treatment tips.
"Ice is very important. If you can ice it several times a day that would be good. Wrapping it has given people relief along with stretching."
Katie is following Dr. Preddy's advice and is now back to doing what she does best -- flying high, with little pain.