Osteoporosis imaging

Osteoporosis was defined at the National Institutes of Health consensus conference as a disease that is associated with a loss of bone mass and a deterioration of bone structure, both of which result in an increased bone fragility and susceptibility to fracture [1]. In 2000, this definition was modified to osteoporosis being defined as a skeletal disorder characterized by compromised bone strength that predisposes to an increased risk of fracture [2,3]. Because this definition seems abstract, the following statements were added: Bone strength reflects the integration of two main features: bone density and bone quality. Bone density is expressed as grams of mineral per area or volume. In any given individual, bone density is determined by peak bone mass and amount of bone loss. Bone quality refers to architecture, turnover, damage accumulation (eg, micro-fractures), and mineralization. Because bone density is the parameter that can be determined best in vivo, has a high precision, and correlates well with the biomechanically determined bone strength (it explains approximately 70% of bone strength [2,3]) the World Health Organization (WHO) defined osteoporosis on the basis of bone mineral density (BMD) [4]. BMD that is more than 2.5 standard deviations below that of a white, young, healthy female adult reference population (T-score) is defined as osteoporosis. BMD that is I to 2.5 standard deviations below that of the young and healthy reference population is defined as osteopenia (Box 1). This definition, however, originally was established only for BMD of the proximal femur (and later of the anteroposterior [AP] spine) determined using dual-energy X-ray absorptiometry (DXA) but has been applied to define diagnostic thresholds at other skeletal sites and for other technologies. Because of the difficulty in accurate measurement and standardization between instruments and sites, controversy exists among experts regarding the continued use of this diagnostic criterion [2,3]. It is also not clear how to apply this diagnostic criterion to ethnic groups and children and men.