Osteoarthritis is the most widespread form of arthritis in the United States. Classically, osteoarthritis has been grouped into primary and secondary types. Primary or idiopathic osteoarthritis is believed to be a sequela of altered biomechanical stresses across joints in susceptible individuals. Secondary osteoarthritis is a consequence of underlying cartilage damage, such as from preceding inflammatory arthritis, metabolic abnormality, or injury. The radiographic hallmark of osteoarthritis is asymmetric loss of cartilage space. Osteophytosis bony eburnation, subchondral cysts, and eventual subluxation follow. Osteoporosis and erosions are not usual features of this disease.