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What Is Arthritis?

In children, arthritis is the inflammation of the lining of the joint’s cover (capsule). When inflamed, this lining makes extra fluid and grows thicker. The overgrown lining and materials leaking from the joint can damage the cartilage and bone and disturb normal bone growth. Tendons have the same lining covering them and can have similar problems, including tendon damage.  

All of these linings are called synovial linings, and inflammation of them is called synovitis. We use the term “arthritis” as shorthand for synovitis of a joint, and “tendonitis” or “tenosynovitis” as shorthand for synovitis of a tendon. 

Arthritis is diagnosed when there is either swelling due to extra fluid or overgrowth of the lining, or two of the following symptoms: increased warmth, pain when extending the range of motion, or loss of full range of motion.