Dual-Energy X-ray Absorptiometry Diagnostic Discordance Between Z-Scores and T-Scores in Young Adults

Diagnostic criteria for postmenopausal osteoporosis using central dual-energy X-ray absorptiometry (DXA) T-scores have been widely accepted. The validity of these criteria for other populations, including premenopausal women and young men, has not been established. The International Society for Clinical Densitometry (ISCD) recommends using DXA Z-scores, not T-scores, for diagnosis in premenopausal women and men aged 20–49 yr, though studies supporting this position have not been published. We examined diagnostic agreement between DXA-generated T-scores and Z-scores in a cohort of men and women aged 20–49 yr, using 1994 World Health Organization and 2005 ISCD DXA criteria. Four thousand two hundred and seventy-five unique subjects were available for analysis. The agreement between DXA T-scores and Z-scores was moderate (Cohen's kappa: 0.53–0.75). The use of Z-scores resulted in significantly fewer (McNemar's p < 0.001) subjects diagnosed with “osteopenia,” “low bone mass for age,” or “osteoporosis.” Thirty-nine percent of Hologic (Hologic, Inc., Bedford, MA) subjects and 30% of Lunar (GE Lunar, GE Madison, WI) subjects diagnosed with “osteoporosis” by T-score were reclassified as either “normal” or “osteopenia” when their Z-score was used. Substitution of DXA Z-scores for T-scores results in significant diagnostic disagreement and significantly fewer persons being diagnosed with low bone mineral density.     

Discordance in DXA male reference ranges.

Previous studies have reported discordance in female lumbar spine and proximal femur dual-energy X-ray absorptiometry (DXA) reference ranges. Although the NHANES III reference range is recommended for the proximal femur in males and females, there are no published data in men on the concordance or otherwise of the different manufacturer-specific lumbar spine bone mineral density (BMD) reference ranges. Potentially, the use of different reference populations by different manufacturers could result in inconsistencies in the diagnosis of osteopenia or osteoporosis. We compared lumbar spine BMD, as well as T-scores and Z-scores, in 45 men scanned using Lunar DPXL and Norland Excel densitometers. The BMD measured by the two instruments was highly correlated (lumbar spine: r = 0.99, p < 0.0001). However, the two instruments assigned significantly different BMD T-scores. These differences relate primarily to the different standard deviations employed in the calculations. There were also significant differences when BMD was expressed with respect to age-matched values (Z-scores). This study shows that in men, as previously demonstrated in women, two commonly used DXA instruments provide comparable lumbar spine standardized BMD, but there are significant differences in derived T-scores because of differences in the manufacturer-specific reference ranges. Standardization of lumbar spine reference ranges in men should be a high priority.     

Definition of Osteoporosis by Bone Density Criteria in Men: Effect of Using Female Instead of Male Young Reference Data Depends on Skeletal Site and Densitometer Manufacturer

Whether to use young male or young female reference data to calculate bone mineral density (BMD) T-scores in men remains controversial. The third National Health and Nutrition Examination and Survey (NHANES III) data show that the mean and standard deviation of femoral neck and total hip BMD is greater in young men than young women, and therefore differences in T-scores at these sites using NHANES III female vs male norms becomes less as BMD decreases. In contrast, manufacturer-specific reference databases generally assume similar standard deviations of BMD in men and women. Using NHANES III reference data for the femoral neck and total hip, respectively we found that men with T-scores of −2.5 when young male norms are used have T-scores of −2.4 and −2.3 when young female norms are used. Using manufacturer-specific reference data, we found that men with T-scores of −2.5 when young male norms are used at the femoral neck, total hip, lumbar spine, or one-third of the forearm would have T-scores ranging from −2.4 to −0.4 when young female norms are used, depending on skeletal site and densitometer manufacturer. The change of proportions of men diagnosed with osteoporosis when young female norms are used instead of young male reference data differs substantially according to skeletal site and densitometer manufacturer.     

Distribution of Z-Scores in a University Cohort With an Emphasis on “High” Bone Mineral Density

High bone mineral density (BMD) is currently not defined by the International Society for Clinical Densitometry with a specific Z-score cutoff; however, it has been suggested that a Z-score greater than or equal to 2.5 is not normal. Institutional Review Board approval was obtained. We evaluated a University dual-energy X-ray absorptiometry database over the previous 24 mo to define Z-score distributions. A Z-score greater than or equal to 2.5 was selected as the outcome event of interest in a logistic regression for adjusted odds ratio. The covariates were height; weight; body mass index (BMI); gender; menopausal status; use of female hormones; presence of insufficiency fractures after 50 yr of age; previous fractures; previous surgeries (back surgeries, vertebroplasty, or kyphoplasty); transplant history; presence of long-term chronic conditions (asthma, lupus, rheumatoid arthritis, or cystic fibrosis); eating disorder; current use of glucocorticoids; smoking status; and current and past use of osteoporosis pharmacological therapies. The study included a total of 8216 patients; 7212 (87.8%) were females, and 1044 (12.2%) were males. In the total population, 13.6% had a Z-score greater than or equal to 2.5 at the lumbar spine, femoral neck, or total hip. Only 0.2% of the males and 0.8% of the females had a Z-score greater than or equal to 2.5 at all 3 sites. The 97.5th percentiles for Z-scores in our population for men and women, respectively, were 3.4 and 3.9 at the lumbar spine, 1.5 and 2.1 at the femoral neck, and 1.6 and 2.2 at the total hip. The 99th percentile for Z-scores for men and women, respectively, were 4.9 and 4.7 at the lumbar spine, 2.4 and 2.7 at the femoral neck, and 2.2 and 2.7 at the total hip. At the lumbar spine, female gender and weight were found to be risk factors for a high Z-score (≥2.5). The use of glucocorticoids, bone-active medications, BMI, and smoking were significantly less likely to predict a lumbar spine Z-score greater than or equal to 2.5. A high total-hip Z-score is predicted by increasing weight, whereas those patients using bone-active medications were less likely to have high BMD at the total hip. At the femoral neck, there were no significant risk factors related to a Z-score greater than or equal to 2.5; those taking bone-active medications were significantly less likely to have a high Z-score. These data suggest that a high Z-score is common at 1 or more sites. Further research about the criteria for the diagnosis of high BMD is warranted.     

Clinical Evaluation of a Phalangeal Bone Mineral Density Assessment System

Because osteoporosis is common and usually managed in primary care, there is a requirement for cheap and convenient methods of measuring bone mineral density (BMD). AccuDEXA (Lone Oak Medical Technologies, Doylestown, PA) is a tabletop dual-energy X-ray absorptiometry (DXA) device that performs BMD measurements of the hand in the middle phalanges of the third finger. The aims of this study were to (1) evaluate the use of AccuDEXA in UK women; (2) investigate the concordance between AccuDEXA T-scores and DXA T-scores for central (spine and hip) sites; (3) investigate the comparative response of AccuDEXA measurements to clinical risk factors for osteoporosis. Measurements of phalangeal and central BMD were performed in 620 women referred by their family doctors for bone densitometry (group 1) and 159 healthy female volunteers (group 2). For 65 women in group 2, aged 39 yr or younger, the mean Z-scores for AccuDEXA and the central sites calculated from US reference ranges were consistent with the expected value of 0, whereas for the 62 group 2 women, aged 50 yr or older, the mean Z-scores for AccuDEXA and the central sites were in the range 0.4–0.7 and were statistically significantly different from 0. In both group 1 and group 2, the AccuDEXA T-scores in older and younger women were systematically higher than those in the central sites by up to 1 unit. Of the 157 women aged 50 yr or older, with osteoporosis, based on their central DXA results, only 34 (22%) had an AccuDEXA T-score less than or equal to ?2.5, whereas 76 (48%) had osteopenia and 47 (30%) were normal based on their AccuDEXA T-scores. When assessed by the effect of clinical risk factors on Z-scores, both AccuDEXA and central BMD were affected to a similar extent. We conclude that the conventional World Health Organisation T-score criteria for the diagnosis of osteoporosis should not be applied to AccuDEXA measurements in UK women. Clinical risk factors for low BMD were found to affect AccuDEXA measurements to a similar extent as central BMD measurements. AccuDEXA measurements could, therefore, provide an alternative method for identifying individuals with low bone mass, provided care is taken in interpreting T-scores, perhaps, through the use of device-specific thresholds.     

Age-related decline in bone mass measured by dual-energy X-ray absorptiometry and quantitative ultrasound in a population-based sample of both sexes: identification of useful ultrasound thresholds for osteoporosis screening.

Quantitative ultrasound (QUS) can be used as a screening tool for low bone mineral density (BMD), but clinical guidelines have not been set. The aim of this population-based, cross-sectional study was to compare age-related changes in bone mass measured by QUS (Lunar, Achilles Plus) and dual-energy X-ray absorptiometry (DXA) in a random sample of 1630 individuals (1041 females, 589 males) 30-85 yr of age. Individuals with DXA T-scores < or =-2.5 at the femoral neck or total hip were identified and receiver operating curves (ROCs) were used to calculate cutoff points for QUS. Sensitivity, specificity, and kappa statistics were calculated. Age-related bone loss was significantly larger with QUS than DXA at all sites in women. For men, the curves were similar for QUS and DXA in the hip. Similar correlations were found between QUS and DXA in different age groups of both sexes (0.36-0.60). For women aged 50-65 yr, a QUS T-score >-1.0 was found to be the most applicable for identifying normal BMD. In the 70-85 yr age group, a T-score <-2.5 for women and a T-score <-0.5 for men seemed reasonable cutoffs for identifying normal BMD (sensitivity: 86-93%; specificity: 28-44%; discordance: 33-73%). Calcaneal QUS cannot be used for the diagnosis of osteoporosis according to WHO criteria, but it can be of use to exclude osteoporosis in 30-40% of our cases.     

In vivo Precision of the GE Lunar iDXA Densitometer for the Measurement of Total-Body, Lumbar Spine, and Femoral Bone Mineral Density in Adults

Knowledge of precision is integral to the monitoring of bone mineral density (BMD) changes using dual-energy X-ray absorptiometry (DXA). We evaluated the precision for bone measurements acquired using a GE Lunar iDXA (GE Healthcare, Waukesha, WI) in self-selected men and women, with mean age of 34.8 yr (standard deviation [SD]: 8.4; range: 20.1–50.5), heterogeneous in terms of body mass index (mean: 25.8 kg/m²; SD: 5.1; range: 16.7–42.7 kg/m²). Two consecutive iDXA scans (with repositioning) of the total body, lumbar spine, and femur were conducted within 1 h, for each subject. The coefficient of variation (CV), the root-mean-square (RMS) averages of SDs of repeated measurements, and the corresponding 95% least significant change were calculated. Linear regression analyses were also undertaken. We found a high level of precision for BMD measurements, particularly for scans of the total body, lumbar spine, and total hip (RMS: 0.007, 0.004, and 0.007 g/cm²; CV: 0.63%, 0.41%, and 0.53%, respectively). Precision error for the femoral neck was higher but still represented good reproducibility (RMS: 0.014 g/cm²; CV: 1.36%). There were associations between body size and total-body BMD and total-hip BMD SD precisions (r = 0.534–0.806, p < 0.05) in male subjects. Regression parameters showed good association between consecutive measurements for all body sites (r² = 0.98–0.99). The Lunar iDXA provided excellent precision for BMD measurements of the total body, lumbar spine, femoral neck, and total hip.     

Effect of Leg Rotation on Hip Bone Mineral Density Measurements

Bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) is widely used in the management of patients with osteoporosis. Factors, which are specific to machine or to operator, can influence the accuracy and precision of BMD estimations. We studied the effect of leg rotation by 10 degrees either internally or externally from the standard position in a group of 50 women (average age 54.9, SD = 11.1 yr) who were free of bone active diseases or medications. External rotation of leg by 10 degrees from the customary position increased the average BMD by 0.005, 0.003, and 0.036 g/cm2 in the femoral neck, trochanter, and Ward's area (p = 0.119, 0.309, and <0.001), respectively. Internal rotation of leg by 10 degrees from the customary position decreased the average BMD by 0.009, 0.005, and 0.006 g/cm2 in the femoral neck, trochanter, and Ward's area (p = <0.001, 0.008, and <0.001), respectively. The number of subjects qualified for the diagnosis of osteoporosis based on the T-scores (equal to or below -2.5) of the femoral neck and trochanter did not change significantly in three different positions (18% in the customary position and after the external rotation and 14% after the internal rotation). A significant change in the femoral neck BMD (defined as 2.77 x precision error) was seen in 12% of subjects after the internal rotation and 8% after the external rotation. Our data emphasize the need for proper positioning of the hip during DXA scanning. Malrotation of the hip can be an important confounding factor when interpreting serial BMD values.     

What is the Number of Older Canadians Needed to Screen by Measurement of Bone Density to Detect an Undiagnosed Case of Osteoporosis? A Population-Based Study From CaMos

Routine bone mineral densitometry (BMD) screening has been recommended for women aged ≥ 65 yr (Osteoporosis Canada [OC], International Society for Clinical Densitometry [ISCD], Canadian and United States Task Forces on Preventative Healthcare, and National Osteoporosis Foundation) and for men ≥ 65 yr (OC) or ≥ 70 yr (ISCD). We estimated the number of older Canadians needed to screen (NNS) by BMD to detect an undiagnosed case of osteoporosis, using prospective, multicenter, population-based data from the Canadian Multicentre Osteoporosis Study (CaMos). We included participants aged ≥ 65 yr with baseline dual-energy X-ray absorptiometry (DXA) BMDs at the femoral neck and lumbar spine (L1–L4). Osteoporosis was defined by a T-score ≤ 2.5 at either site. Patients were questioned about a prior diagnosis of osteoporosis. We studied 2699 women and 1032 men aged ≥ 65 yr. The percentage prevalence and 95% confidence intervals were determined. In individuals aged ≥ 65 yr, the prevalence of osteoporosis was 25.6% in women (95% confidence interval, 24.0%, 27.3%) and 8.9% in men (7.3%, 10.8%). In 652 men aged ≥ 70 yr, the prevalence of osteoporosis was 11.3% (9.1%, 14.0%). Of the participants with BMD-defined osteoporosis, 76.6% of woman aged ≥ 65 yr (73.2%, 79.6%; 516 of 674 women), 93.4% of men aged ≥ 65 yr (86.4%, 96.9%; 85 of 91), and 93.2% of men ≥ 70 yr (84.9%, 97.0%; 68 of 73) were not aware of it. Thus, the minimum NNS by BMD testing to detect one previously undiagnosed case of osteoporosis in Canada is: 6 women aged ≥ 65 yr, 13 men aged ≥ 65 yr, and 10 men aged ≥ 70 yr.     

Discordance in lumbar spine T-scores and nonstandardization of standard deviations.

Previous studies have demonstrated differences in proximal femur bone mineral density T-scores depending on the reference range used. This subsequently was addressed by the recommended adoption of the National Health and Nutrition Examination Survey III reference range. There is, however, no accepted reference range for interpretation of lumbar spine bone mineral density (BMD), and the use of different reference populations by different manufacturers could result in inconsistencies in diagnosis of osteopenia or osteoporosis. We compared lumbar spine BMD, as well as T- and Z-scores, in 59 women measured using Lunar DPXL and Norland Excel densitometers. BMD measured by the instruments was highly correlated (r = 0.98, p < 0.0001). The instruments however assigned significantly different values when BMD was expressed as T-scores. There were also significant differences in BMD assignments between instruments, when expressed as Z-scores. The observed differences relate to the different young normal mean, and SD employed in calculating the T- and Z scores. To conclude, in the lumbar spine, two commonly used DXA instruments provide comparable absolute values but there are significant differences in derived T-scores due to differences in manufacturer- specific reference ranges. There is a need for standardization of the reference ranges used in the lumbar spine.     

Normative Bone Mineral Density Z-Scores for Canadians Aged 16 to 24 Years: The Canadian Multicenter Osteoporosis Study

The objectives of the study were to develop bone mineral density (BMD) reference norms and BMD Z-scores at various skeletal sites, to determine whether prior fracture and/or asthma were related to BMD, and to assess possible geographic variation of BMD among Canadian youth aged 16–24 yr. Z-Scores were defined as the number of standard deviations from the mean BMD of a healthy population of the same age, race, and sex. Z-Scores were calculated using the reference sample defined as Canadian Caucasian participants without asthma or prior fracture. Reference standards were created for lumbar spine (L1–L4), femoral neck, total hip, and greater trochanter, by each year of age (16–24 yr), and by sex. The Z-score norms were developed for groups noted earlier. Mean Z-scores between the asthma or fracture subgroups compared with the mean Z-scores in the reference sample were not different. There were minor differences in mean BMD across different Canadian geographic regions. This study provides age, sex, and skeletal site-specific Caucasian reference norms and formulae for the calculation of BMD Z-scores for Canadian youth aged 16–24 yr. This information will be valuable to help to identify individuals with clinically meaningful low BMD.     

Geographical variation in DXA bone mineral density in young European men and women. Results from the Network in Europe on Male Osteoporosis (NEMO) study

We collected population-based young normal hip and spine BMD data from 17 centres across Europe to assess between centre differences and to compare reference values with the US NHANES-III data. There was strong evidence of between country heterogeneity, but not between centres within countries. Hip BMD mean values were lower in European women, but SD's differed little from the NHANES-III USA results in both sexes. It may be necessary to adjust NHANES-III based T-scores by adding/subtracting a country-specific adjustment factor. INTRODUCTION: It remains unclear whether young normal BMD reference values specific to an American population can be validly used for T-score calculation in Europeans. METHODS: We collected population based BMD data from 1163 men and 329 women aged 19-29 years from 17 centres across Europe to compare mean and SD values with the NHANES-III study USA results. BMD(g/cm2) was measured at the hip and spine using DXA densitometers cross-calibrated with the European Spine Phantom (ESP). The only exclusions were for technically inadequate scans. A linear regression model was used to derive reference values. To allow for direct comparison with published NHANES III study data, the cross-calibrated BMD values were converted using the ESP equations to Hologic QDR 1000 units. RESULTS: In men, the overall mean(SD) BMD values expressed in Hologic-QDR1000 units of measurement, were: femoral neck 0.912(0.132); trochanter 0.793(0.124); and L2-L4 spine 1.027(0.123). The respective estimates in women were: 0.826(0.115); 0.670(0.093); and 0.983(0.107). However the I2 statistic for heterogeneity indicated moderate to strong evidence of between-centre heterogeneity. There was, however, no significant heterogeneity observed between centres within countries, suggesting that this variation arose from national differences. Compared to the NHANES III population-based US data, the mean values in women were significantly lower at both sites due to some lower national European means. However, at all sites and in both sexes the SD's were very similar between the US and Europe. There was some evidence that recruiting volunteers resulted in biased values in women. CONCLUSION: Our T-score normal values for the lumbar spine (L2-L4) should be more reliable for spine-specific risk assessment than some non-representative normal ranges, and should be evaluated for that purpose in Europe. If T-scores are to be used to compare individual data with ranges seen in normal young subjects of the same nationality, it may be necessary to adjust femoral NHANES III-based T-scores by adding (or subtracting) a country-specific adjustment factor. In risk assessment it is probably sufficient to use NHANES III-based hip T-scores, as supplied for the hip by densitometer manufacturers, interpreting them in light of recent international meta-analysis data on the relationship between BMD and fracture risk.     

Heterogeneity of Bone Mineral Density Across Skeletal Sites and Its Clinical Implications

Low trauma fractures in the elderly are highly predictable by measurement of bone mineral density (BMD). Preventive measures for low BMD, such as hormone replace therapy (HRT), have potential risks. Thus, a rational decision on HRT or other therapy critically depends on an accurate diagnosis of osteopenia/osteoporosis. We assessed the degree of diagnostic heterogeneity based on spine and hip BMD for 2313 women. We found: 1. In ~30.0% of cases, the difference between spine and hip Z- and T-scores was >1.0, and in 20.8% (Z-scores) and 15.2% (T-scores) the difference was >2.0. 2. With increasing age, the proportions of women with Z- or T-scores greater at the hip than the spine generally decreased. 3. The correlation between hip and spine and Z- and T-scores ranged from 0.50 to 0.72, and generally decreased with increasing age. 4. If screened only at the hip or spine, 17.9/27.3% with osteopenia and 1.3/2.9% with osteoporosis at either site would be diagnosed as normal. Corresponding analyses of 143 men yielded similar results. Therefore, if possible, dual X-ray absorptiometry (DXA) of both the spine and hip should be performed for an accurate assessment of osteoporosis at these two most frequently fractured sites. If only one site is chosen, measurement of the hip is preferred to measurement of the spine.     

Diagnostic agreement at the total hip using different DXA systems and the NHANES III database.

In 1997, the National Health and Nutrition Examination Survey III (NHANES III) total hip reference database was adopted for T-score derivation in an effort to optimize diagnostic agreement among densitometers from different manufacturers. Our study was undertaken to evaluate the effectiveness of the NHANES III standardized database at achieving agreement in diagnostic classification (normal, osteopenia, or osteoporosis) based on total hip T-scores comparing 2 different dual-energy X-ray absorptiometry (DXA) systems. This was a retrospective analysis of standard bilateral hip and lumbar spine scans done in duplicate for 60 women scanned on both a GE Lunar Prodigy and Hologic Delphi DXA system. Classification based on lumbar spine T-scores using manufacturer-specific databases was also compared as no standardized lumbar spine reference database exists. Subject's mean age was 62 yr (range: 47-83 yr). There was no statistically significant difference in diagnostic classification between DXA systems (Prodigy vs Delphi), with agreement (same women classified same way) of 92% at the left total hip. Agreement was 100% when T-scores were greater than or equal to -0.8 and less than or equal to -1.2. There was 90% agreement between DXA systems at the lumbar spine. For both hip and spine, all diagnostic discrepancies occurred when the T-scores were at or near transition thresholds between normal and osteopenia or osteopenia and osteoporosis. The difference in mean T-scores between DXA systems at left total hip was 0.11 vs 0.32 for lumbar spine (p less than 0.001). Use of the NHANES III standardized database results in good diagnostic agreement at total hip between Prodigy and Delphi.     

Identification of rheumatoid arthritis patients with vertebral fractures using bone mineral density and trabecular bone score

The aim of this study was to test bone mineral density (BMD), trabecular bone score (TBS), and their combination, for detection of rheumatoid arthritis (RA) patients with vertebral fractures (VFs). One hundred eighty-five women aged 56.0 ± 13.5 yr, with RA since 15.5 ± 9.9 yr were studied. Lumbar spine, total hip, and femoral neck BMD were assessed by dual-energy X-ray absorptiometry (DXA). TBS was calculated from anteroposterior image of lumbar spine BMD. VFs from T4 to L4 were evaluated using Vertebral Fracture Assessment software on DXA device. The proportions of patients with VF and T-scores ≤-2.5 were only 24.2%, 21.2%, and 33.3% at lumbar spine, total hip, and femoral neck, respectively. T-scores were significantly lower in patients with VF than in patients without VF, the largest difference being observed at femoral neck (p=0.0001). TBS was significantly lower in patients with VF vs without VF (p=0.0001). The areas under the curves were 0.621, 0.704, 0.703, 0.719, and 0.727 for lumbar spine BMD, TBS, lumbar spine BMD+TBS, total hip BMD, and femoral neck BMD, respectively. The threshold of 1.173 for TBS had the best sensitivity (63%) and specificity (74%). TBS measured at the lumbar spine has a better discrimination value than lumbar spine BMD, and similar to femoral neck BMD, for prediction of presence of VF in patients with RA. In RA subjects with osteopenia, the proportion of patients with VF was higher in the lowest tertile of TBS when compared with the highest tertile. In this population, at low risk according to BMD, TBS could help to detect patients with VF.     

The Ability of Hand Digital X-Ray Radiogrammetry to Identify Middle-Aged and Elderly Women With Reduced Bone Density, as Assessed by Femoral Neck Dual-Energy X-Ray Absorptiometry

In this study, we evaluate the ability of digitized digital X-ray radiogrammetry (DXR) bone mineral density (BMD) to identify women with reduced BMD at femoral neck, assessed by dual-energy X-ray absorptiometry (DXA). The study population contained women with recent low-energy distal radius fracture and women recruited from the general population, all aged 50 yr or older. The correlation between hand BMD and femoral neck BMD was r = 0.65 (p < 0.001). We used a triage approach where 2 cutoffs for DXR T-score were defined at which patients with 90% sensitivity and 90% specificity could be identified to have or not have reduced BMD at femoral neck, defined as T-score ≤ ?2.5 standard deviation (SD). The upper and lower DXR T-score cutoffs were ?1.2 and ?2.7, respectively. Applying the triage approach in the whole cohort, 32% would require a central DXA assessment to determine the presence or absence of femoral neck T-score ≤ ?2.5 SD. Our data suggest that DXR can be used to reduce the numbers of patients in need of DXA femoral neck and may, thus, be of clinical value where access to DXA is limited.     

Biomechanical indices of the femoral neck estimated from the standard DXA output: age- and sex-related differences.

We explored the feasibility of using routine dual-energy X-ray absorptiometry (DXA) to estimate several parameters of femoral neck geometry related to bone strength and to analyze their changes with age. Bone mineral density (BMD) was measured in 871 control men and women and in 19 women with hip fracture. Volumetric BMD (volBMD) and geometrical parameters were estimated from the DXA output with previously published formulas. In young subjects, areal BMD was higher in men than in women, but volBMD was similar in both sexes. However, it showed a more rapid decline with age in women. The femoral neck width and cortical thickness were also higher in young men than in women. Neck width increased and cortical thickness decreased with age in both sexes. The buckling ratio, an index of local cortical instability, increased more rapidly in women. The compressive strength decreased progressively with age in women, whereas it did not change in men after 50 yr of age. Compressive strength and the buckling ratio showed the largest difference between control and hip fracture women (Z=-1.3). This cross-sectional study suggests that data available in the standard DXA output can easily be used to estimate several geometrical parameters of the femoral neck that evolve in a sex- and age-specific manner. Further studies are needed to elucidate whether they add significant information to BMD in the prediction of fracture risk.     

Sex Differences in the Association Between Adiponectin and BMD,Bone Loss,and Fractures: The Rancho Bernardo Study

We evaluated sex differences in the prospective association between adiponectin with BMD, bone loss, and fractures. Adiponectin, an adipose‐derived protein with insulin‐sensitizing properties, is also expressed in bone‐forming cells. Conflicting results and sex differences in the adiponectin‐BMD association have been reported in cross‐sectional studies. Serum adiponectin was measured in fasting blood samples obtained in 1984–1987 in 447 postmenopausal women (mean age: 76 yr) and 484 men (mean age: 75 yr). Four years later, BMD was measured at the midshaft radius by single photon absorptiometry and at the femoral neck, total hip, and lumbar spine by DXA. In 1992–1996, axial BMD was remeasured in 261 women and 264 men. Multivariable analysis adjusted for age, weight, calcium intake, type 2 diabetes, alcohol intake, and exercise. Among women, adiponectin was inversely associated with BMD at the femoral neck (β = ?0.002, p = 0.007), total hip (β = ?0.002, p = 0.009), lumbar spine (β = ?0.003, p = 0.008), and midshaft radius (β = ?0.002, p = 0.01) after 4.4 yr and at the femoral neck and total hip 8.6 yr later. Among men, adiponectin was inversely associated with BMD at the femoral neck, (β = ?0.002, p = 0.03), total hip (β = ?0.004, p < 0.001), and midshaft radius (β = ?0.003, p < 0.001) after 4.4 yr and at the hip 8.6 yr later. Adiponectin was not associated with 4‐yr bone loss in either sex but was associated with vertebral fractures (adjusted OR: 1.13; 95% CI: 1.08–1.23; p = 0.009) among men only. Adiponectin was inversely associated with BMD; however, sex differences were observed by anatomical site and with regards to vertebral fractures.     

The prevalence of significant left-right differences in hip bone mineral density

Introduction We determined the prevalence of left-right differences in hip bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA) and the resultant consequence, namely: the frequency at which patients would be classified differently if lumbar spine and only one hip (rather than both hips) were measured.Methods This was a retrospective DXA scan reanalysis of 3012 white women ≥50 yrs who had scans of both hips using Hologic DXA systems. The difference between left and right hips was considered significant if it exceeded the least significant change (LSC) for any of three hip subregions (total hip, femoral neck, trochanter). The number of women with osteoporosis in both hips, the left hip only, or the right hip only was determined by lowest T-score from total hip, femoral neck, or trochanter.Results Despite high left-right correlations of subregion BMD, significant left-right differences in BMD were common: the difference exceeded the LSC for 47% of women at total hip, 31% at femoral neck, and 56% at trochanter. Left-right differences in BMD that exceeded the LSC affected the percent agreement of left-right hip classification: for all women irrespective of spine status, there was 77% classification (diagnostic) agreement in hip pairs in which the left-right hip BMD difference exceeded the LSC versus 87% agreement in which LSC was not exceeded (significant difference in proportions, P<0.0001). The greatest risk of different classification would occur in women with normal spines as the diagnosis might be determined by hip T-scores. Using L1-4 lumbar spine T-scores, 1229 women were normal at the spine. Twenty-four (2%) were osteoporotic at both hips. However, 12 women (1%) were osteoporotic only in the left hip (significantly different from zero, P<0.001) and 11 (1%) only in the right hip (P<0.001); of these 23 women, the difference in BMD between the osteoporotic hip and the contralateral hip exceeded the LSC in 16 (70% of those with osteoporosis in only one hip). Using L1-4 lumbar spine T-scores, 1159 women were osteopenic at the spine. Of these, 126 (11%) were osteoporotic at both hips, 54 (5%) only in the left hip (P<0.001), and 42 (4%) only in the right hip (P<0.001); of these 96 women, the difference in BMD between the osteoporotic hip and the contralateral hip exceeded the LSC in 56 (58% of those with osteoporosis in only one hip).Conclusions A statistically significant number of women with osteoporosis are potentially classified differently when scanning only one hip as a result of the high prevalence of left-right differences in BMD. Although the percentages are low, the total number of women affected may be large. From a public health perspective, the practice of scanning both hips could potentially identify more women with osteoporosis and may help prevent future hip fractures.     

The Prevalence of Osteoporosis: Gender and Racial Comparison

Osteoporosis is common among the growing population of older men: almost 20% of men > or = 50 years old have osteoporosis of the hip, spine, or wrist. However, the exact estimate depends on the approach taken to normalize for bone size, the specific skeletal site assessed, and the diagnostic criteria used. Bone mineral density (BMD, g/cm2) by DXA is 12-25% greater in men than women, but bone mineral apparent density (g/cm3) is similar in the two sexes. This correction for skeletal size largely eliminates apparent differences in areal BMD between the races and also reduces the apparent effects on BMD of age. The particular skeletal site that is assessed has an important influence on the prevalence of osteoporosis (sex-specific BMD T-score less than -2.5) in men which varies from 0 to 36%, depending on the site, and from 2% to 45% in postmenopausal women. The discrepancies relate mainly to different patterns of bone loss at the various sites, but estimates are also affected by the specific young normal means and standard deviations (SD) used to calculate the T-scores. A greater mean and smaller SD among normal young men in Rochester, MN produced a higher prevalence of osteoporosis at the femoral neck (22% vs 7%) compared with estimates for white men from the Third National Health and Nutritional Examination Survey; use of female normal values further reduced osteoporosis prevalence at the hip in white, Hispanic, and African-American men to 4%, 2%, and 3%, respectively, compared with 20% for white women in the United States. By contrast, fracture risk is similar for men and women at any given level of BMD. These observations reinforce current efforts to move away from osteoporosis prevalence and toward absolute fracture risk as the main basis for clinical treatment decisions.