Osteoarthritis is a common condition which affects the joints, most commonly the hips, knees or hands.  It typically affects the DIP and PIP joint of the fingers and the CMC (base joint) of the thumb, making them feel painful and stiff.  It is a medical condition, caused by wearing down of cartilage and joint inflammation.  It is associated with hereditary factors (if one or more of your family has hand arthritis), gender (it is more common in women than in men), a previous hand injury and increasing age. It is not a piano-related injury as such, but it can be exacerbated by high-intensity wear and tear (overuse) of joints in professional pianists who practise intensely.  Moderate piano playing, however, is often recommended as a healthy, therapeutic activity which keeps the joints supple. 

Pianists with arthritis may find that the stiffness and malformation limits their strength and agility at the keyboard and they may need to find ways to manage the condition and modify their technique to work around any changes that occur. If intense practice sessions exacerbate pain in the joints, they may need to reduce practice time or take more regular breaks. 

This article focuses mainly on osteo-arthritis affecting the hands.