What does a non reactive jra arthritis mean?

Many different names: I believe that you are referring to an arthritis that is occurring in a juvenile that is negative for rheumatoid factor test- a test for rheumatoid arthritis seen more in adults. This currently is called juvenile idiopathic arthritis while it used to be called juvenile rheumatoid arthritis factor negative. There are many different types or subcategories of this as this arthritis.

No infectious cause!: It means there is no infectious cause. Nonethless, it is almost certainly not rheumatoid arthritis in children, but what is now called juvenile idiopathic arthritis. This need not be crippling, and most can lead a perfectly normal life, including sports, with medications available.