Paget's disease, also called osteitis deformans, is a chronic bone disorder in which there is abnormal bone remodelling (the process of bone breakdown and rebuilding). With Paget's disease, bone is broken down more quickly and is then replaced with softer, more porous bone. As a result, affected bones become thicker, weaker, and deformed. It usually affects the bones of the skull, pelvis, collarbone, spine, and legs.
Paget's disease affects about 3% of people over the age of 40, but the exact number is not known since many people don't know they have the condition. It seems to affect more men than women. Although this disease is found around the world, it appears more commonly in Europe and Australia.