How long should i wait before starting cheer again?

Okay so on October 28, 2010, i dislocated my kneecap at cheerleading. I ended up having to get it snaped back into place by a doctor, and was on crutches for about three months, and had to sit out of gym class for about 5 months.It is still brusied and often gets swollen during bad weather. I don't know when i should shart cheering again though, because i don't want to hurt it because i started to soon after getting hurt. How long should i wait?