Arthritis is a condition that affects the joints of the body, including the joints of the feet. There are different forms of arthritis, two of the most common being osteoarthritis and rheumatoid arthritis. Osteoarthritis is the gradual wearing down of the joint lining, and Rheumatoid Arthritis is an autoimmune disease where the white blood cells begin to attack the lining of the joint, called the synovium lining. When rheumatoid arthritis occurs in the feet, the synovium becomes inflamed and destroys the joints of the feet, as well as the ligaments and tissues that support them. Damage to ligaments can result in deformities, such as hammertoe and bunions.