Peripheral bone densitometry: an old friend revisited

The earliest assessments of bone "mass" involved metacarpal morphometry that provided insight into age-related changes, the effects of low habitual dietary calcium intake, and the effects of estrogen deficiency and replacement. Single photon absorptiometry (SPA) made quantitative mass measurement possible but this was intellectually unsatisfactory since osteoporotic fractures are more of a concern at the spine and hip than at the wrist. Necessity forced the development of axial bone mass measurement (dual photon absorptiometry--DPA, dual energy xray absorptiometry--DXA, quantitative computed tomography--QCT). Hip measurements provide a better prediction of hip fracture risk than measurements at any other skeletal site. For every standard deviation decrement of bone mass at the hip, relative risk of fracture is 3.0. At non-hip sites the relative risk is only 2.0 for each standard deviation decrement in bone mass. However measurement at non-hip sites provide a fracture risk prediction that is at least the equal of blood pressure measurement for predicting risk of CVA, and substantially better than the risk assessment of acute MI afforded by cholesterol measurement. An important caveat of the superiority of hip measurement is that the data are derived from short-term studies in older women (> 70 years). The relative risk data from phalangeal, forearm, and heel measurements have all been obtained from longer-term studies in younger women. From a community health perspective, bone density measurements, no matter how accurate, precise, and meaningful, have limited value if access to the technology is limited. Peripheral measurements can be obtained on existing radiographic equipment (phalanges), or small, portable, inexpensive dedicated equipment (forearm, heel). This technology is more likely to make it to the office of the primary care physician than the larger, more expensive, dedicated equipment needed for hip measurements. The peripheral measurement technology is also suitable for high traffic areas, just as blood pressure and cholesterol measurements are widely available. This presentation reviewed the scientific validity of peripheral bone mass measurement and explored the potential for making this technology available at non-traditional facilities such as pharmacies, shopping malls, health clubs, etc.