To understand the pathogenesis of arthritis, we have to first understand the normal anatomy of a joint. A joint consists of two bones coming together to allow smooth movement. It is surrounded by other structures which assess in normal functioning of a joint. These surrounding structures include cartilage, tendons, ligaments, and surrounding muscles. Most of the joints are lined by a thin film of tissue called synovium, which covers the joint from inside. This synovium produces joint fluid in small quantities, which acts as a lubricant for smooth joint movement. Different type of arthritis affect different structures within the joint. In case of osteoarthritis, there is loss of cartilage in between the joints, which leads to joint pain, swelling, and limited movement. In case of rheumatoid arthritis, there is significant inflammation and growth in the synovial lining, which leads to joint destruction.