Arthritis is simply inflammation of a joint. This title is a little misleading as not all types of arthritis involve inflammation!
Forms of arthritis fall into two main groups; inflammatory arthritis, and osteoarthritis also called degenerative joint disease depending on where in the world you live. Inflammatory arthritis, including rheumatoid arthritis, is caused by the bodies own immune system, or occasionally an infection, attacking the lining of a joint. Osteoarthritis on the other hand is caused by general wear and tear on a joint.
The treatments of arthritis are diverse and depend greatly on the type of arthritis you have. It is best treated using a team approach involving your GP, a Rheumatologist, a Podiatrist, a Physiotherapist, and an Exercise Physiologist. Your podiatrist would usually treat arthritis using orthotics.