It's called Juvenile Rheumatoid Arthritis when you are young. You can grow out of it but I think it will return at some point in your life. Then it's Rheumatoid Arthritis if in fact it was JRA when you were young. Or maybe it's still called JRA. Here is a site on it.

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001487/