What is Arthritis? in Sclero Forums (MAIN) Posted July 1, 2011 · Report reply 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.