Comparison of DXA hip structural analysis with volumetric QCT.

Hip structural analysis (HSA) estimates geometrical and mechanical properties from hip dual-energy X-ray absorptiometry (DXA) images and is widely used in osteoporosis trials. This study compares HSA to volumetric quantitative computed tomography (QCT) measurements in the same population. A total of 121 women (mean age 58 yr, mean body mass index 27 kg/m2) participated. Each woman received a volumetric QCT scan and DXA scan of the left hip. QCT scans were analyzed with in-house software that directly computed geometric and mechanical parameters at the neck and trochanteric regions. DXA HSA was performed with an implementation by GE/Lunar. Pair-wise linear regression of HSA variables was conducted by method to site matched QCT variables for bone density, cross-sectional area, and cross-sectional moment of inertia (CSMI) of the femur neck. HSA correlated well with QCT (r2=0.67 for neck bone mineral density [BMD] and 0.5 for CSMI) and standard DXA at the neck (r2=0.82 for BMD). HSA and volumetric QCT compared favorably, which supports the validity of a projective technique such as DXA to derive geometrical properties of the proximal hip.

Effect of precision error on T-scores and the diagnostic classification of bone status.

We quantified confidence intervals (CIs) for T-scores for the lumbar spine and hip and determined the practical effect (impact on diagnosis) of variability around the T-score cutpoint of -2.5. Using precision data from the literature for GE Lunar Prodigy dual-energy X-ray absorptiometry (DXA) systems, the 95% CI for the T-score was +/-0.23 at the lumbar spine (L1-L4), +/- 0.20 at the total hip, and +/-0.41 at the femoral neck. Thus, T-score variations of +/-0.23 or less at the spine, +/-0.20 at the total hip, and +/-0.41 at the femoral neck are not statistically significant. When diagnosing osteoporosis, T-scores in the interval -2.3 to -2.7 for spine or total hip (after rounding to conform to guidelines from the International Society for Clinical Densitometry) and -2.1 to -2.9 for femoral neck are not statistically different from -2.5. Better precision values resulted in smaller 95% CIs. This concept was applied to actual clinical data using Hologic DXA systems. The study cohort comprised 2388 white women with either normal or osteopenic spines in whom the densitometric diagnosis of osteoporosis would be determined by hip T-scores. When evaluating actual patient T-scores in the range -2.5+/-95% CI, we found that the diagnosis was indeterminate in approximately 12% of women when T-scores for femoral neck were used and in 4% of women when T-scores for total hip were used, with uncertainty as to whether the classification was osteopenia or osteoporosis. We conclude that precision influences the variability around T-scores and that this variability affects the reliability of diagnostic classification.

The tale of the T-score: review and perspective.

The T-score is well known to anyone working in the field of bone densitometry. It is the primary output from a bone densitometry system and is most often used for diagnosis of osteoporosis and for making treatment decisions. Despite widespread acceptance of the T-score, most clinicians are unfamiliar with the historical evolution of the T-score as a clinical measure. Furthermore, evidence is mounting that the T-score is not the optimal diagnostic parameter for clinical decision making. Many additional risk factors have been reported which can be combined with bone density results to assess absolute fracture risk. This editorial provides an historical review of the T-score, followed by summary of the status of the T-score, and concludes with suggestions for the future use of the T-score in bone densitometry.

Improving femoral bone density measurements.

Femoral bone density measurements are clinically important because of their strong relationship with hip fracture. However, current densitometers have not improved upon femoral densitometry since the introduction of dual-energy X-ray absorptiometry (DXA) systems. Recently, several advances in DXA measurement of the proximal femur have been proposed by various published studies. These advances can be added to existing DXA systems, while maintaining the conventional femoral regions of interest. Both upper neck bone mineral density (BMD) and hip axis length have been reported to be associated with hip fractures. With newer technology that enables a rapid assessment of both hips, bilateral femur measurements are now clinically practical and are of importance in those with T-scores approaching, yet not reaching, diagnostic or therapeutic thresholds. Bilateral femur measurements also reduce precision error compared to a single femur measurement, yielding precision errors less than observed at the spine. With this decrease in precision error, monitoring of bone changes is now possible at the femur with the utility comparable to the spine.

Automated assessment of exclusion criteria for DXA lumbar spine scans.

Modern bone densitometry systems using dual-energy X-ray absorptiometry (DXA) automatically analyze lumbar spine scans and provide clinically important information concerning spine bone mineral density (BMD) and fracture risk. Lumbar spine BMD accurately reflects skeletal health and fracture risk in most cases, but degenerative diseases associated with aging may lead to the formation of reactive bone (osteophytes) and other confounding conditions that elevate BMD without a concomitant increase in bone strength or decrease in fracture risk. Automated densitometry software known as computer-aided densitometry (CAD) (GE Medical Systems Lunar) assists the user in identifying scans with common acquisition and analysis irregularities known to influence BMD values. Visual examination of 231 female spine scans measured with DXA found abnormal conditions that could influence BMD results in 29% of scans. The sensitivity and specificity of several criteria for identifying scans with conditions that could influence BMD were determined. A good criterion for identifying scans with abnormal conditions was a T-score difference of greater than 0.9 or 1.0 between L1-L4 mean and individual vertebrae. Criteria for excluding affected vertebrae were determined. Exclusion of affected vertebrae resulted in a mean BMD decrease of nearly 0.6 SD (T-score) among affected scans.

Prediction of fracture risk in postmenopausal white women with peripheral bone densitometry: evidence from the National Osteoporosis Risk Assessment.

Low bone mineral density (BMD) is a risk factor for fracture. Although the current "gold standard" test is DXA of the hip and spine, this method is not universally available. No large studies have evaluated the ability of new, less expensive peripheral technologies to predict fracture. We studied the association between BMD measurements at peripheral sites and subsequent fracture risk at the hip, wrist/forearm, spine, and rib in 149,524 postmenopausal white women, without prior diagnosis of osteoporosis. At enrollment, each participant completed a risk assessment questionnaire and had BMD testing at the heel, forearm, or finger. Main outcomes were new fractures of the hip, wrist/forearm, spine, or rib within the first 12 months after testing. After 1 year, 2259 women reported 2340 new fractures. Based on manufacturers' normative data and multivariable adjusted analyses, women who had T scores < or = -2.5 SD were 2.15 (finger) to 3.94 (heel ultrasound [US]) times more likely to fracture than women with normal BMD. All measurement sites/devices predicted fracture equally well, and risk prediction was similar whether calculated from the manufacturers' young normal values (T scores) or using SDs from the mean age of the National Osteoporosis Risk Assessment (NORA) population. The areas under receiver operating characteristic (ROC) curves for hip fracture were comparable with those published using measurements at hip sites. We conclude that low BMD found by peripheral technologies, regardless of the site measured, is associated with at least a twofold increased risk of fracture within 1 year, even at skeletal sites other than the one measured.

Implications in the use of T-scores for the diagnosis of osteoporosis in men.

Osteoporosis is recognized as a disorder of both men and women. However, the World Health Organization's (WHO) definition of osteoporosis (a bone mineral density [BMD] T-score of -2.5 or less) was formulated for use with postmenopausal women only. In the absence of a BMD-based definition for male osteoporosis, the WHO definition is often applied to men as well. Several important questions exist when considering the use of T-scores in men. First, is the WHO definition appropriate for men? What is the impact of using a -2.5 criteria, in terms of the number of men that would be identified as osteoporotic? When calculating T-scores in men, should male or female young normal values be used? Can the same T-score criteria be used for all skeletal sites and technologies? To address these questions, osteoporosis prevalence estimates for men aged 50 yr and over were generated using WHO methods and manufacturer normative data from dual-energy X-ray absorptiometry (DXA), quantitative computed tomography (QCT), and ultrasound. Estimates were determined for several skeletal sites and technologies using both male and female young normal values. Prevalence estimates were compared to published fracture risk estimates. Mean T-scores declined with age at all measurement sites. Discrepancies were found between the different skeletal sites and techniques, similar to the previously reported differences in women. A -2.5 criterion (based on young normal males or females) appeared to underestimate the prevalence of osteoporosis, except for QCT, which seemed to overestimate risk. Depending on the technique used, 0 to 12.5 million US men 50 yr of age and older would be classified as osteoporotic using the WHO definition. T-Scores based on male norms were less discordant across skeletal sites than female-based T-scores. Male-based T-scores between -1.8 and -2.3 using DXA and ultrasound and -3.1 for QCT provided osteoporosis prevalence estimates that approximated the likelihood of common fractures in men 50 and over. We conclude that the use of single T-score-based criterion for the diagnosis of osteoporosis in men has many potential difficulties. BMD measurement techniques provide discrepant estimates of prevalence and may underestimate the size of the male population at risk for fracture. Based on available normative data, a -2.5 criterion underestimates osteoporosis prevalence in men, whether based on male or female norms. Prospective studies are needed to further refinement to the BMD definition of osteoporosis in men.