Osteoarthritis is classified as primary (idiopathic) or secondary to some known cause.
Primary osteoarthritis may be localized to specific joints (eg, hands, knee, hip). If primary osteoarthritis involves multiple joints, it is classified as generalized osteoarthritis.
Secondary osteoarthritis results from conditions that change the microenvironment of the cartilage or joint structure. These conditions include significant trauma, congenital joint abnormalities, metabolic defects (eg, hemochromatosis, Wilson disease), infections (causing postinfectious arthritis), endocrine and neuropathic diseases, and disorders that alter the normal structure and function of hyaline cartilage (eg, rheumatoid arthritis, psoriatic arthritis, calcium crystal deposition disease).