Osteoarthritis (OA) is the most common joint disease in humans and all vertebrate animals. Nearly 50 percent of the population suffers from osteoarthritis by age 65. Osteoarthritis is a chronic disease of the joints, especially the weight-bearing joints that develops when the linings of joints degenerate, leading to inflammation, pain, and decreased mobility and function. Current thinking is that osteoarthritis is not just a single disorder, but a complex pattern of changes in the repair mechanisms that keep joints functioning normally. A number of different factors can impinge upon the health of joint tissue, including biomechanical forces, changes in body biochemistry, inflammatory processes, and altered immune function.