Prevention is particularly important in osteoporosis since the loss of bone strength that accompanies bone loss is not known to be reversible. Identification of those at risk by measurement of risk factors may help target prevention efforts. Low bone mass and a propensity for falling are established risk factors for osteoporotic fracture in the elderly; some other risk factors for fracture may operate through these two pathways. There has been little epidemiologic study of other potential causes of fracture such as poor bone quality and trauma biomechanics, and little is known about risk factors that may operate through these pathways.