Knee cap getting caught in missing cartilage groove

I had a LR a year ago and when my doctor went in he saw where I had a lot of cartilage damage behind my kneecap. He smoothed it down but when he did that it caused a huge groove. Now whenever I am walking or standing up my kneecap gets caught in that groove and it is very painful. I am only 15 and I am very active in sports so this hinders my playing ability. My doctor says that is just the way it is going to be, but I was wondering if there is anyone else having these problems and what they do for it.