Arthritis (or osteoarthritis) is the most common type of joint problem in older people. It usually affects knees, hips, hands, spine, or sometimes shoulders. Rheumatoid arthritis is the second most common type of chronic arthritis. It is caused by an auto-immune reaction in which your body’s immune system mistakenly attacks joint tissues. Most typically, it involves the joints in your fingers, wrists, elbows, knees, ankles, and toes. Other types of arthritis include gout or pseudogout. Sometimes, there is a mechanical problem in the joint, such as torn cartilage, that causes pain or limits movement in the joint.