Osteoarthritis (OA, also known as degenerative arthritis,degenerative joint disease), is a group of diseases and mechanicalabnormalities involving degradation of joints, including articular cartilage and the subchondralbone next to it. Clinical manifestations of OA may include jointpain, tenderness, stiffness, creaking, locking of joints, and sometimes localinflammation. 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 bodystruggles to contain ongoing damage, immune and regrowth processes canaccelerate damage. When bone surfaces become less well protected by cartilage,subchondral bone may be exposed and damaged, with regrowth leading to aproliferation of ivory-like, dense, reactive bone in central areas of cartilageloss, a process called eburnation. The patient increasingly experiences pain uponweight bearing, including walking and standing. As a result of decreasedmovement because of the pain, regional muscles may atrophy,and ligamentsmay become more lax. OA is the most common form of arthritis and the leadingcause of chronic disability in the United States.
"Osteoarthritis" is derived from the Greek word "osteo", meaning "of thebone", "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 notto be confused with rheumatoid arthritis, an autoimmune disease with joint inflammation as amain 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 iscorrelated with OA incidence, this correlation may illustrate that OA is aprocess that takes time to develop -- or that repair and regeneration that maykeep pace with damage in the joints of younger people do slow with age. Thereis sometimes a diagnosable underlying cause for OA, in which case it isdescribed as secondary OA. Inthe majority of cases no cause can be identified, described as primary OA. "Degenerativearthritis" is often used as a synonym for OA, but the latter involves bothdegenerative and regenerative changes.
OA affects about 8 million people in the United Kingdom and nearly 27million people in the United States, where it accounts for 25% ofvisits to primary care physicians and half of all NSAID (Non-SteroidalAnti-Inflammatory Drugs) prescriptions. It is estimated that 80% ofthe USpopulation will have radiographic evidence of OA by age 65, although only 60% ofthose will show symptoms.In the United States,hospitalizations for osteoarthritis soared from about 322,000 in 1993 to 735,000 in 2006
The main symptom is acute pain, causing loss of abilityand often stiffness. "Pain" is generally described as a sharp ache,or a burning sensation in the associate muscles and tendons. OA cancause a crackling noise (called "crepitus")when the affected joint is moved or touched, and patients may experience musclespasmand contractions in the tendons. Occasionally, the joints may also be filledwith fluid. Humid and cold weather increases the pain in many patients.
OA commonly affects the hands, feet,spine,and the large weight bearing joints, such as the hipsand knees,although in theory, any joint in the body can be affected. As OA progresses,the affected joints appear larger, are stiff and painful, and usually feel worse, the more they are usedthroughout the day, thus distinguishing it from rheumatoid arthritis.
In smaller joints, such as at the fingers, hard bony enlargements, called Heberden'snodes (on the distal interphalangeal joints) and/or Bouchard'snodes (on the proximal interphalangeal joints), may form, and thoughthey are not necessarily painful, they do limit the movement of the fingerssignificantly. OA at the toes leads to the formation of bunions,rendering them red or swollen. Some people notice these physical changes beforethey experience any pain.
OA is the most common cause of joint effusion, sometimes called water on theknee in lay terms, an accumulation of excess fluid in oraround the knee joint.