Osteoarthritis is a degenrative joint disease, it is the most common chronic arthritis of the joint. The causes of arthritis could be obesity, injury to the joint or even genetic. It also can be secondary to other diseases such as rheumatoid arthritis or hemochromatosis. The most common symptoms of OA are stiffness of the joint early in the morning and pain. Treatment is by medication for stages 1-3, stage 4 is an indication for knee replacement or surgery.