Osteoarthritis (OA) is the most common form of arthritis, affecting millions of people around the world. The degenerative disease is caused by aging joints, injury and obesity, and it occurs when the protective cartilage on the ends of bones wears down over time. OA can damage any joint in the body, but it most commonly affects joints in hands, the neck, lower back, knees and hips. Signs and symptoms include pain in joints during or after movement, tenderness, stiffness, loss of flexibility, grating sensation and bone spurs. OA gradually worsens with time, but treatments can slow the progression of the disease, help relieve pain and improve joint function.