Osteoarthritis is the gradual breakdown of the material, called cartilage, that covers the joint. Cartilage is a tough elastic material that acts as a shock absorber. In osteoarthritis, the cartilage becomes thinner and may even disappear in some places. When this happens, bone rubs against bone, causing pain. Under this weakened cartilage, the bone tries to regenerate and forms growths, called spurs or osteophytes. The joint may become deformed, larger, and lose its mobility.

Osteoarthritis (OA) of the finger joints ("knobbly OA") is the most common joint disease in adults. Although we still have a lot to learn about the causes of hand osteoarthritis, there is a significant family predisposition and it is more common in women over the age of 45. This type of osteoarthritis may occur after one or more injuries, or as a result of certain rare diseases that change the characteristics of the cartilage.

Normal	Heberden's nodes	Bouchard's nodes
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It generally begins with the gradual appearance of small symmetrical knobs on the back of the end joints of the fingers (Heberden's nodes), mainly the index and middle fingers. This form of osteoarthritis can be painless or can cause episodes of pain corresponding to the appearance of the nodes. Over time, the fingers may become deformed. More rarely, small cysts filled with a gelatinous fluid precede the appearance of the nodes. In general, they resolve on their own. Bouchard's nodes are less common and often affect the middle joints of the fingers; they are often more painful than Heberden's nodes. Increasing difficulty in bending the joints is a rare, later consequence of this type of osteoarthritis.

Erosive

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Erosive hand osteoarthritis is a rare form of the disease. It affects the end and middle joints of the fingers. Compared to other types of osteoarthritis of finger joints, this form can result in more severe pain, larger bone spurs, and more important deformity. This can mean reduced flexion and mobility of affected joints.