RA is a malfunction of the immune system in which it mistakes joint tissue, mainly the cartilage, as something that must be attacked and eliminated. This causes
the typical swelling, redness, heat, and over time, damage that causes
pain and disability. Cartilage is eaten away; even connective tissue such as tendons and ligaments can be affected as well.
The confusion often arises because RA damage *can* lead to OA in the joints; however, OA does NOT cause RA. Make sense?