I am in my 30's now, but when I was 8 years old, I had OS in my knee, which is more rare for a girl. I got it from falling down hard on my knee while playing tennis. The sports medicine doctor's my parents took me to said that it normally goes away on it's own in 2 years. If not, surgery would be needed, and then, only when I stopped growing. Needless to say, mine never went away, so when I turned 16, I had surgery to remove it. I have a 3 inch scar across my knee. The doctor removed the OS as well as about an inch of my hamstring. I was in a full leg brace for 4 months and had to use crutches an additional 4 months after that, because your leg muscle pretty much dies after being inactive for that long. The surgery is rare, at least it was when I had it done 15 years ago, so rare, especially in a girl, that they got my parent's permission to film it for medical students. I still have some pain till this day in my knee, especially when it rains or snows, etc... and I have "Traumatic arthritis" because of it. But it's much better than the pain I had at ages of 8-16. I'm sure they must have better ways of dealing with it now. Like I said, that was about 15 yeas ago...