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Overview of dual-energy x-ray absorptiometry

E Michael Lewiecki, MD
Section Editor
Clifford J Rosen, MD
Deputy Editor
Jean E Mulder, MD


Osteoporosis or low bone mass (osteopenia) occurs in approximately 53 million American men and women, accounting for 55 percent of the population age 50 years and over [1]. Osteoporosis is defined as "a skeletal disease characterized by compromised bone strength predisposing a person to an increased risk of fracture" [2].

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 [3]. Fractures of the spine and hip are associated with chronic pain, deformity, depression, disability, and death. Approximately 50 percent of patients with hip fractures will never be able to walk without assistance and 25 percent will require long-term care [4]. The mortality rate five years after a fracture of the hip or a clinical VF is approximately 20 percent greater than expected [5]. The direct cost of incident osteoporotic fractures in the United States was approximately $17 billion per year in 2005 [3].

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" [6]. 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. Trabecular bone score (TBS) is a gray-level textural measurement that can be extracted from a dual-energy x-ray absorptiometry (DXA) image of the lumbar spine with proprietary software; it captures information related to bone microarchitecture that provides an assessment of fracture risk that is independent of bone density [7]. For now, in the absence of a fragility fracture, bone density is the best predictor of fracture risk.

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Literature review current through: Nov 2017. | This topic last updated: Oct 25, 2017.
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