BMD measurements derived from DXA has been shown to accurately predict fracture risk [18,19]. Epidemiological studies have demonstrated that BMD correlates to population fracture risk and amount of force necessary to fracture bone [20,21]. In a routine DXA study, 2 sites (the lumbar spine and hip) are reported. In the spine, a frontal projection measures up to 4 vertebral bodies from L1 to L4, and in the hip, a frontal projection measures 2 regions: the femoral neck and total hip [17]. In the event of a falsely elevated BMD of the lumbar spine caused by fracture, facet joint osteoarthritis, or spondylosis, up to 2 vertebral levels may be excluded from analysis. However, if exclusion of more than 2 vertebral body levels is necessary, then the second hip can be scanned as a substitute for the spine [22]. Alternatively, the distal one-third radius of the nondominant arm may be used as a third site in situations in which only one hip is available. Otherwise, the distal one-third radius is used primarily in patients with hyperparathyroidism. Primary hyperparathyroidism preferentially decreases mineralization at cortical-rich sites such as the hip and mid radius, in contrast to the predominantly cancellous bone of the lumbar spine [22]. Although DXA is an accurate screening tool, it remains underused. According to 2 recent reports, only 6.7% of patients underwent evaluation with DXA 6 months after sustaining a fragility fracture in 1 study, and only 8% of patients on long-term glucocorticoid therapy had follow-up DXAs [29,30]. Underutilization may lead to under- treatment in approximately 70% of these patients, and patients who are not adequately treated are at increased risk of incurring additional fractures in their lifetime [7,29]. QCT QCT QCT also provides volumetric BMD (vBMD), and both the trabecular and cortical bone compartments can be assessed [31,32].
Osteoporosis and Bone Mineral Density. BMD measurements derived from DXA has been shown to accurately predict fracture risk [18,19]. Epidemiological studies have demonstrated that BMD correlates to population fracture risk and amount of force necessary to fracture bone [20,21]. In a routine DXA study, 2 sites (the lumbar spine and hip) are reported. In the spine, a frontal projection measures up to 4 vertebral bodies from L1 to L4, and in the hip, a frontal projection measures 2 regions: the femoral neck and total hip [17]. In the event of a falsely elevated BMD of the lumbar spine caused by fracture, facet joint osteoarthritis, or spondylosis, up to 2 vertebral levels may be excluded from analysis. However, if exclusion of more than 2 vertebral body levels is necessary, then the second hip can be scanned as a substitute for the spine [22]. Alternatively, the distal one-third radius of the nondominant arm may be used as a third site in situations in which only one hip is available. Otherwise, the distal one-third radius is used primarily in patients with hyperparathyroidism. Primary hyperparathyroidism preferentially decreases mineralization at cortical-rich sites such as the hip and mid radius, in contrast to the predominantly cancellous bone of the lumbar spine [22]. Although DXA is an accurate screening tool, it remains underused. According to 2 recent reports, only 6.7% of patients underwent evaluation with DXA 6 months after sustaining a fragility fracture in 1 study, and only 8% of patients on long-term glucocorticoid therapy had follow-up DXAs [29,30]. Underutilization may lead to under- treatment in approximately 70% of these patients, and patients who are not adequately treated are at increased risk of incurring additional fractures in their lifetime [7,29]. QCT QCT QCT also provides volumetric BMD (vBMD), and both the trabecular and cortical bone compartments can be assessed [31,32].