Arthritis - National Library of Medicine - PubMed Health: "Arthritis is inflammation of one or more joints. A joint is the area where two bones meet. There are over 100 different types of arthritis.
Causes, incidence, and risk factors
Arthritis involves the breakdown of cartilage. Cartilage normally protects a joint, allowing it to move smoothly. Cartilage also absorbs shock when pressure is placed on the joint, such as when you walk. Without the normal amount of cartilage, the bones rub together, causing pain, swelling (inflammation), and stiffness."
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