Radiologic bone assessment in the evaluation of osteoporosis.

Osteoporosis affects nearly 28 million elderly Americans. Its major clinical manifestation is fragility fractures of the spine, hip, and distal radius. Low bone mass is the most important risk factor for a fragility fracture. In 1994, the World Health Organization defined osteoporosis on the basis of a bone mineral density that is 2.5 standard deviations below that in peak young normal persons. Three common imaging modalities used to assess bone strength are dual-energy x-ray absorptiometry, quantitative computed tomography, and calcaneal ultrasonography. The first two modalities measure bone mineral density in both the lumbar spine and peripheral sites. It is thought that calcaneal ultrasonography measures bone architecture and density. Unlike the other studies, ultrasonography currently cannot be used for monitoring skeletal changes over time or evaluating response to therapy.