Bone densitometry has become an important tool in the diagnosis and management of osteoporosis. The methods available include dual X-ray absorptiometry (DXA), quantitative computed tomography (QCT) as well as quantitative ultrasound (QUS), applied to the axial and appendicular skeleton. All the techniques have strengths and limitations, of which users should be aware. The most widely available method used in clinical practice is DXA of lumbar spine (L1-L4) and proximal femur (total hip). In recent years smaller, less expensive, devices are available for forearm and calcaneus measurements. DXA measures integral (cortical and trabecular) bone. Bone mineral density (BMD) measurements at any site is predictive of fracture risk, but measurements at any specific site optimises fracture risk prediction. DXA provides an "areal" density in g/cm2, and so is size dependent, a particular problem in growing children and in patients in whom disease has caused small stature. QCT overcomes this problem by providing a true volumetric density in mg/cm3, and measures cortical and trabecular bone separately. Since trabecular bone is some 8x more metabolically active than cortical bone, QCT has the potential to be sensitive to monitor change. The ratio of cortical to trabecular bone varies in different skeletal sites, so measurements in various sites may provide complementary information in research studies. DXA images must be carefully scrutinised to ensure no artefacts are present which will falsely elevate or reduce BMD. For interpretation, appropriate reference data must be available. The WHO definition of osteoporosis (T score below -2.5) is only applicable to DXA spine, hip and forearm; not to calcaneus nor to QCT and QUS. The advantages of QUS are that the scanners are small and portable, relatively inexpensive, and to not use ionising radiation. The main scientific studies published to date have used QUS applied to the calcaneus and hand phalanges. If monitoring changes in BMD an interval of at least 18-24 months should intervene between measures; a statistically significant changes is 2.8x precision (coefficient of variation, CV%). The lumbar spine is optimum for monitoring changes. The precision of a long established technique (metacarpal index, MCI, measured on hand radiographs) has been improved by the application of computer analysis methods.
|Translated title of the contribution||Bone densitometry in the diagnosis and follow-up of the elderly patient|
|Number of pages||5|
|Journal||Giornale di Gerontologia|
|Issue number||SUPPL. 1|
|Publication status||Published - Feb 2004|
ASJC Scopus subject areas
- Geriatrics and Gerontology