Bone mass measurement: how, where, when and why?
Delmas, P.D.
International Journal of Fertility and Menopausal Studies 38(Suppl 2): 70-76
1993
ISSN/ISBN: 1069-3130 PMID: 8252108 Document Number: 408678
Low bone mass, by far the major causal factor in osteoporotic fractures, cannot be predicted from the clinical evaluation of risk factors for osteoporosis. Measurement of bone mass is commonly achieved by using dual-energy X-ray absorptiometry (DXA), which has replaced dual-photon absorptiometry (DPA); single-energy X-ray absorptiometry (SXA), which is likely to replace I-125 single-photon absorptiometry; and by using quantitative computed tomography (QCT). Measurement of ultrasound speed and attenuation across the calcaneum is another promising method still under investigation. Each method may have some advantage or disadvantage relating to practical aspects (cost, scanning time, availability) and technical aspects (radiation dose, accuracy, precision). Several clinical situations have been identified in which measurement of bone mass will be useful, including women after the menopause to select those who should receive bone-sparing agents, and patients with x-ray vertebral deformity to confirm the diagnosis of osteoporosis. DXA allows measurement of bone mass at different skeletal sites, including the lumbar spine (by anteroposterior and lateral view), the hip, the forearm, and the total skeleton. The choice of the site to be screened will often be dictated by clinical considerations such as age and associated osteoarthritis, but, in theory, should be oriented by the ability of bone mass measurement at each site to predict osteoporotic fractures. Several prospective studies have shown that a decrease of 1 standard deviation of bone mass is associated with a 1.5- to 3-fold increase of the relative risk of fracture. Measuring any site is probably equally predictive of the risk of all osteoporotic fractures, while measurement of the hip appears to be a better predictor of the risk of hip fracture.