What is Arthritis? in Sclero Forums (MAIN) Posted July 1, 2011 What is Arthritis? There are many types of arthritis. The most common types are osteoarthritis, rheumatoid arthritis, and psoriatic arthritis, though all have different pathologies. Newsmax.com. 06/06/11. (Also see: Arthritis) These items were posted in the ISN Newsroom. Check the Newsroom every day for the latest scleroderma medical and support information.