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![[image of someone with knee pain]](http://cdn1.medicalnewstoday.com/content/images/articles/314/314154/an-image-of-someone-with-knee-pain.jpg)
Rheumatoid arthritis (RA) is an autoimmune condition characterized by inflammation of the joints. It is different from osteoarthritis, which is caused by wear and tear in the joints.
RA affects up to 1.3 percent of the worldwide population, according to the Centers for Disease Control and Prevention (CDC).
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