Osteoarthritis, also known as osteoarthrosis or, more commonly, degenerative joint disease, is a disorder that affects the joints. At the joint, the surfaces of the bones are lined with tissue called cartilage.
Cartilage provides a smooth surface for movements.
Sometimes, the cartilage between bones softens, and some of its fibres separate. The normally smooth cartilage becomes pitted and frayed, and whole segments of cartilage may be lost. Bony outgrowths form which interfere with the movement of nearby tendons and joints. These changes make movement of the joint more difficult and very painful and are signs of degenerative joint disease or osteoarthritis. The cause of degenerative joint disease is not known.