ABSTRACT
DEFINITION/OVERVIEW Osteoporosis is a chronic progressive disease characterized by low bone density, micro - architectural bone deterioration, and decreased bone strength leading to increased bone fragility and increased fracture risk. In 1994 the World Health Organization (WHO) published criteria for the diagnosis of osteoporosis based upon bone mineral density (BMD). Normal BMD is defined as a BMD value within 1 standard deviation of the young adult female reference mean and is designated as a T-score ≥–1. The young adult female reference mean is calculated from the mean BMD of healthy females aged 20-29 of a single ethnicity. Low bone mass (osteopenia) is defined as a BMD that is between 1 and 2.5 standard deviations below the young adult mean and is designated as a T-score <–1 and >–2.5. Osteoporosis is defined as a BMD 2.5 standard deviations or more below the young adult mean designated as a T-score <–2.5. Lastly, severe osteoporosis is defined as a BMD 2.5 standard deviations or more below the young adult mean in the presence of one or more fragility fractures. In current clinical practice, the diagnosis of osteoporosis is based either upon the WHO criteria described above or the presence of fragility fractures. These types of fractures occur with low-impact trauma, such as falling from a standing position.
