Overview of dual-energy x-ray absorptiometry
- E Michael Lewiecki, MD
E Michael Lewiecki, MD
- New Mexico Clinical Research & Osteoporosis Center
Osteoporosis or low bone mass (osteopenia) occurs in about 53 million American men and women, accounting for 55 percent of the population age 50 years and over . Osteoporosis has been defined as “a skeletal disease characterized by compromised bone strength predisposing a person to an increased risk of fracture” .
There are approximately two million fragility fractures in the United States each year: 547,000 vertebral fractures (VFs), 297,000 hip fractures, 397,000 wrist fractures, and 675,000 at other skeletal sites . Fractures of the spine and hip are associated with chronic pain, deformity, depression, disability, and death. About 50 percent of patients with hip fractures will never be able to walk without assistance and 25 percent will require long-term care . The mortality rate five years after a fracture of the hip or a clinical VF is about 20 percent greater than expected . The direct cost of incident osteoporotic fractures in the United States was about $17 billion per year in 2005 .
This topic review will discuss the clinical applications and interpretation of dual-energy x-ray absorptiometry (DXA) in evaluating osteoporosis. Other aspects of screening for osteoporosis are reviewed elsewhere. (See "Screening for osteoporosis".)
Bone strength is determined by bone mineral density (BMD) and other properties of bone that are often collectively called “bone quality” . Non-BMD determinants of bone strength include bone turnover, architecture (size and shape, or bone geometry), microarchitecture (eg, trabecular thickness, trabecular connectivity, trabecular perforation, cortical thickness, and cortical porosity), damage accumulation, matrix properties, mineralization, and mineral properties (eg, crystal size and orientation).
Investigation of bone quality has provided insight into the pathogenesis of osteoporosis and a better understanding of the mechanism of action of medications used to treat osteoporosis, but with the exception of bone turnover markers it is not yet possible to measure these routinely in clinical practice. Technologies such as high resolution peripheral quantitative computed tomography (HR-pQCT) and micro-magnetic resonance imaging (micro-MRI) can be used to assess trabecular microarchitecture, but at the present time these are largely used for research, with no established clinical applications. For now, in the absence of a fragility fracture, bone density is the best predictor of fracture risk.
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- BONE QUALITY
- BMD testing
- DXA TECHNOLOGY
- CLINICAL APPLICATIONS OF DXA
- Skeletal site selection
- Reference databases
- Diagnosis of osteoporosis
- - Postmenopausal women
- - Premenopausal women
- - Men
- - Children
- Serial BMD testing
- - Precision assessment
- - Time interval for repeating DXA
- - Skeletal site to monitor
- - Validity of comparisons
- - Interpretation of BMD changes
- Vertebral fracture assessment
- INFORMATION FOR PATIENTS
- SUMMARY AND RECOMMENDATIONS