Osteoarthritis is a disease generally associated with aging and is characterized by progressive destruction of the cartilage. In general, the cartilage is supple and covers the end of the bones. In osteoarthritis, it becomes thinner and then cracks. Cartilage debris is then found in the synovial fluid, and the synovial membrane tries to remove the debris. The joint becomes inflamed and secretes a large amount of fluid. It swells, heats and becomes painful.