Osteoarthritis (OA) is widely recognized as the most common form of arthritis, and a major cause of pain and disability among US adults. Estimates of prevalence vary depending on how OA is defined: radiographic, symptomatic radiographic, or symptomatic only (self-reported presence of pain, aching, or stiffness). Radiographic OA is reported at higher prevalence levels than symptomatic, but symptomatic OA is more often cited from the self-reported databases.