Bone mineral density of the radius: where do we stand?

one mineral density measurements are useful for predicting the risk of fracture in an individual, for assessing the effect of a disease or drug on bone mass, and for monitoring the effect of therapy of osteoporosis. For the hip and spine, measurements made at the affected site discriminate better between fragility fractures and nonfracture cases than do measure ments made on other parts of the skeleton (1,2). Nonetheless, there is renewed interest in measuring bone mineral density at other sites e.g., the radius. Single-photon absorptiometry equipment is less expensive than dual-photon absorptiometry apparatus, and iodine-125 sources are less expensive than gadolinium-i 53 or americium-241 sources. The area of bone measured is smaller and more uniform, and posi tioning is usually simpler. The spine is commonly subject to deformities, such as hypertrophic spurs, that do not contribute to bone strength, kyphoscoliosis, and vertebral fractures. Cal cium deposits in the aorta may also falsely elevate the estimated lumbar spine density. The regions of the radius studied previously have been composed mainly of cortical bone. Figure 1 shows the location of the so-called â€oe10%,†• â€oe1/3,†• and â€oe50%†• sites. These propor tions refer to the length along the ulna, not the radius. Figure 2 is taken from Schienker and von Seggen (3,4) and shows the distribution of bone mineral content and percentage of trabe cular bone along the radius. Since the â€oe10%†• site is actually about 12†" 15% of radius length, the percentage trabecular bone at this site is less than 25% and the percentage of trabecular bone at the â€oe1/3†• and â€oe50%†• sites is less than 10%. These sites are therefore mainly cortical bone whereas the vertebrae are made up of predominantly trabecular bone (5). Measure ments made on the radius are often in the â€oenormal range†• for age in patients with vertebral fractures (6). Also, the effect of aging differs at the two sites. Bone density of the lumbar spine appears to decline after the age of 35 yr in women (6†" 8) whereas in the midradius and distal radius the decline does not begin until after the menopause (9). In the past year, three groups have reported their experiences using single-photon absorp tiometry to study the radius at the site where the percentage of trabecular bone is similar to that found in the lumbar spine, a site referred to as the â€oeultradistal†…