There are many methods to obtain animal models of osteoporosis, such as surgical induction [40] (removal of bilateral ovaries/testes), drug induction [41] (adrenocortical hormone and other drugs), loss induction, diet induction [42] (low calcium diet), gene knockout [43] (knockout of the OPG gene), and spontaneous degeneration. The gene discussed is TNFRSF11B; the disease is osteoporosis.