What is arthritis? how often do teens get it (percentage) and how do they get it? will mark

Arthritis doesn't affect young people as much as it does adults, but lots of teens still get it. Arthritis is an inflammation  (swelling and irritation) of the synovial (pronounced: suh-no-vee-ul) membrane, which lines the joints (like the knees or knuckles). When it becomes inflamed, fluid is produced. The joints can become stiff, swollen, painful, and warm to the touch. Over time, inflammation in a joint can damage the cartilage and bone.

"Idiopathic" is a medical word that doctors use to describe a disease that has no known cause. Juvenile idiopathic arthritis is the most common kind of arthritis among kids and teens. Kids usually find out they have this disease between the ages of 6 months and 16 years. (You also might hear JIA called "juvenile rheumatoid arthritis," or JRA.)

Explanation:

all the above is what i would say