Osteoarthritis (OA, also known as degenerative arthritis, degenerative joint disease), is a group of diseases and mechanical abnormalities involving degradation of joints, including articular cartilage and the subchondral bone next to it. Clinical manifestations of OA may include joint pain, tenderness, stiffness, creaking, locking of joints, and sometimes local inflammation. In OA, a variety of potential forces—hereditary, developmental, metabolic, and mechanical—may initiate processes leading to loss of cartilage -- a strong protein matrix that lubricates and cushions the joints. As the body struggles to contain ongoing damage, immune and regrowth processes can accelerate damage. When bone surfaces become less well protected by cartilage, subchondral bone may be exposed and damaged, with regrowth leading to a proliferation of ivory-like, dense, reactive bone in central areas of cartilage loss, a process called eburnation. The patient increasingly experiences pain upon weight bearing, including walking and standing. As a result of decreased movement because of the pain, regional muscles may atrophy, and ligaments may become more lax. OA is the most common form of arthritis,
"Osteoarthritis" is derived from the Greek word "''osteo''", meaning "of the bone", "''arthro''", meaning "joint", and "''itis''", meaning inflammation, although the "itis" of osteo arthritis is somewhat of a misnomer -- inflammation is not a conspicuous feature of the disease. Osteoarthritis is not to be confused with rheumatoid arthritis, an autoimmune disease with joint inflammation as a main feature. A common misconception is that OA is due solely to wear and tear, since OA typically is not present in younger people. However, while age is correlated with OA incidence, this correlation may illustrate that OA is a process that takes time to develop -- or that repair and regeneration that may keep pace with damage in the joints of younger people do slow with age. There is usually an underlying cause for OA, in which case it is described as ''secondary OA''. If no underlying cause can be identified it is described as ''primary OA''. "Degenerative arthritis" is often used as a synonym for OA, but the latter involves both degenerative and regenerative changes.
OA affects nearly 27 million people in the United States, accounting for 25% of visits to primary care physicians, and half of all NSAID (Non-Steroidal Anti-Inflammatory Drugs) prescriptions. It is estimated that 80% of the population will have radiographic evidence of OA by age 65, although only 60% of those will show symptoms.
In the United States, hospitalizations for osteoarthritis soared from about 322,000 in 1993 to 735,000 in 2006.
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