Its easy to understand how one might assume osteoarthritis (OA) and rheumatoid arthritis (RA) have similar causes and treatments, because arthritis is arthritis, right? Yes, they are the two most common types of arthritis. And both conditions share similar characteristics. But thats where the similarities end: In fact, OA and RA are quite different. Cleveland Clinic rheumatologist Linda Mileti, MD, helps us understand these two forms of arthritis, how each progresses and the best treatment for each.