Osteoarthritis usually affects the joints and might cause pain. The cartilage on joints wears and thins so the bone beneath the cartilage thickens and forms outgrowths which make your joint roughened with small protrusions. The knee joint may also appear enlarged as the area around the knee thickens and becomes inflamed. If Paget's disease affects a joint, then the risk of osteoarthritis is increased because of repeated stress on the joints.
Attribution: BUPA