Pain in a joint can be caused by mechanical factors, neurological factors, or inflammation. While neuro-mechanical factors predominate in osteoarthritis (OA), inflammation is the primary cause of joint pain in rheumatoid arthritis (RA). When articular cartilage is worn away and bone is exposed, simple pressure on the bone surface will cause pain. The articular cartilage itself does not become inflamed, but instead the joint lining, or synovium, develops inflammation, called synovitis. Nonsteroidal anti-inflammatory drugs (NSAIDs) are an effective treatment for joint inflammation and should be taken to relieve pain caused by synovitis. Arthritis can occur in any joint, from the smallest to the largest. Joints that are frequently traumatized, such as the knee, have a higher incidence of OA. It is believed that joint instability caused by trauma can predispose a joint to OA at an early age.