Arthritis. Coloured X-ray of arthritis affecting the joints of the hand. The thumb joint is seen to be both rougher and misaligned compared to a normal joint. The most common type of arthritis is osteoarthritis, which results from wear and tear on the joints. This can be caused by genetic or metabolic factors, and occurs usually in middle age. Rheumatoid arthritis is the most severe, and is an autoimmune disorder, where the immune system attacks the joints. Anti-inflammatory drugs help in treatment.