Arthritis is a group of conditions involving damage to the joints of the body. There are different types of arthritis, each having a different cause. The most common form is osteoarthritis, a degenerative joint disease that is a result of trauma to the joint, infection of the joint or age. Another type of arthritis is where the body attacks itself (autoimmune diseases). Examples of this kind are rheumatoid arthritis and psoriatic arthritis. Septic arthritis is caused by an infection of the joint. Gouty arthritis is caused by deposition of uric acid crystals in the joint, which causes inflammation. There is also an uncommon form of gout called pseudogout that is caused by the formation of rhomboid crystals of calcium pyrophosphate.