Psoriasis is a skin disease in which patients have dry, red and scaly skin rashes that can occur on any part of the body. Between 5-20% of patients with psoriasis may develop an associated arthritis. Arthritis means inflamed joint. A normal joint consists of two cartilage-covered bone surfaces that glide smoothly against one another. In psoriatic arthritis, the lining of the joint—the synovium—becomes inflamed and swollen. The swollen tissues stretch supporting structures of the joints, such as ligaments and tendons. As these supporting structures stretch out, the joints become deformed and unstable. The gliding surface wears out, and joint cartilage and bone erode. In addition to the hands, psoriatic arthritis can affect joints in the spine, feet, and jaw.