Osteoporosis and bone mineral densitometry.

Osteoporosis is a common cause of vertebral and hip fractures and although their occurrence depends on a variety of factors, bone mineral density (BMD) is the most important determinant. Methods of measuring BMD are therefore pertinent to identify individuals with reduced bone mass and at increased risk of fracture, and current techniques provide accurate and precise BMD measurements with low radiation dose. The methods most widely used are single photon absorptiometry; dual photon absorptiometry, which has been replaced by dual energy x-ray absorptiometry; and quantitative CT. Dual energy x-ray absorptiometry permits BMD measurement in the lumbar spine, femoral neck, forearm, and whole body. Bone strength is also related to trabecular width and arrangement. The newer techniques of broadband ultrasound attenuation and MR imaging (T2*) offer potential for investigating both trabecular bone mass and structure, as does high-resolution CT. These methods provide powerful tools for the study of the skeleton in health and disease and have established roles in appropriate clinical circumstances. Although BMD measurement can provide an estimate of fracture risk, there are limitations to fracture prediction in an individual subject, but efforts are being made to improve the discriminatory and predictive aspects of BMD.