Arthritis will cause you to feel pain or stiffness in your body. It may also limit your movement. This is caused when your joints become swollen. Joints are where two bones meet, such as your elbow and knee. One type of arthritis, osteoarthritis, is often related to aging or to an injury. Other types occur when your immune system, which normally protects your body from infection, attacks your body's own tissues. Rheumatoid arthritis is the most common form of this kind of arthritis. Juvenile rheumatoid arthritis is a form of the disease that happens in children.