Bone assessment in elderly women: what does a low bone ultrasound result tell us about bone mineral density?

Access to dual energy X-ray absorptiometry (DXA) can prove difficult for frail or elderly patients, and bone ultrasound may offer a practical alternative. Even after adjustment for bone mineral density (BMD), ultrasound readings are able to predict hip fracture in elderly women. We consider how bone ultrasound might contribute to bone assessment in a clinical setting. DXA remains the gold standard for bone assessment, with osteoporosis defined as a BMD result more than 2.5 S.D. below the young adult mean. Using an equivalent approach we defined an osteoporotic ultrasound result as broadband ultrasound attenuation (BUA)<54 dB/MHz. In 73 women aged 29-86 (mean 65) years DXA was used to measure BMD at lumbar spine and hip, and ultrasound to measure BUA at the heel. Correlation of BUA with BMD at femoral neck (r=0.64, P<0.001), and lumbar spine (r=0.55, P<0.001) was consistent with previously reported figures for this ultrasound system. All subjects with BUA below the 54 dB/MHz threshold value were shown to have low femoral neck BMD. Women (42%) aged over 65, but only 18% of younger women had low BUA results. In women over 65 years of age measurements of BUA achieved a sensitivity of 61% and specificity of 100% in prediction of low femoral neck BMD. Although a normal BUA did not exclude an osteoporotic BMD result at hip or lumbar spine, a low BUA appeared a highly specific predictor of low BMD at these sites. Since all those women identified as having a low BUA at the heel also had low BMD results, ultrasound appeared to identify a subgroup of elderly patients at a very high risk of fracture.