Arthropathies, by definition, are joint-centered processes. If the bone surface on only one side of the joint is affected, the disease process is unlikely to be a primary arthropathy. Hyaline cartilage that lines the articular bone along the joint surface is critical for proper function of the joint. Its loss is a common finding in most arthropathies, whether productive or inflammatory in nature. Radiographically, this loss is seen as reduction in joint space. With loss of cartilage, the denuded ends of the bones that make up the joint rub against one another, leading to new bone formation (termed eburnation when described grossly and seen as subchondral new bone formation on radiographs). In addition, osteophytes form, as a response to abnormal stresses across the joint. The radiographic sine qua non for osteoarthritis (whether primary or secondary to other arthritidies or disease processes) is the trio of joint space narrowing, subchondral sclerosis and osteophyte formation.