Arthritis is the inflammation of a joint or joints of the body. The inflammation occurs when the autoimmune system is affected, and it attacks the joints instead of repairing the body, hence the ligaments and tendons in the joints become inflamed. There are many types of arthritis, and this depends on the causes, but the most common ones are rheumatoid arthritis, which is an autoimmune disorder and osteoarthritis which happens when the cartilage wears down.