The term degeneration in medicine means deterioration or decline of function of a cell, tissue or an organ with time, usually as a person ages. Osteoarthritis, osteoporosis, atherosclerosis and Alzheimer disease are well known examples. Degenerative conditions occur in everyone as everybody will age without fail (i. e. "natural" degeneration) often after age of 40-50 but some degenerative conditions can occur at younger age (i. e. "acquired") after an injury (accident or overuse), an infection, or after inheriting a hereditary disease (e. g. ankylosing spondylitis of the spine).