they re located either alone or in pairs within cavities in the tissue they constantly renewed the cartilage replacing old fibers and protein chains with new ones. that usually works well for many years. but then something strange happens. for some people earlier and others later. something happens in the joints the cells begin to destroy the cartilage they restart their original developmental program and break down the cartilage like they did at the embryo stage some cartilage cells end up dying others transform into bone cells the cartilage starts turning into bone. bony growths develop on the sides of the joint they further restrict the joints mobility.