Monitoring of dual-energy X-ray absorptiometry measurement in clinical practice.

Bone densitometry has become the "gold standard" in osteoporosis diagnosis and treatment evaluation. It has also become more and more common to perform a second dual-energy X-ray absorptiometry (DXA) measurement to monitor bone mineral density (BMD) status or the effect of therapeutic intervention. When a second measurement is performed on a patient, the clinician needs to distinguish between a true change in BMD and a random fluctuation related to variability in the measurement procedure. The reproducibility of DXA measurements is claimed to be good. Such variability is due to multiple causes, such as device errors, technician variability, patients' movements, and variation due to other unpredictable sources. The precision error is usually expressed as the coefficient of variation (CV). However, several other statistics to express reproducibility exist such as the smallest detectable difference (SDD) or the least significant change (LSC). The SDD represents a cut-off that can be measured in an individual and is usually considered more useful than the CV in clinical practice. Indeed, the use of the SDD is preferable to the use of the CV and LSC because of its independence from BMD level and its expression in absolute units (g/cm2). At each measurement center, the SDD must be calculated from in vivo reproducibility data. The choice of the optimum time and site for performing follow-up scans depends on the ratio of the expected BMD treatment effect to the precision of the measurements.     

DXA测量骨密度的精密度评估及其应用

目的通过短期精密度实验,统计分析双能X线吸收测定法(dual energy X-ray absorptiometry,DXA)测量骨密度(bone mineral density,BMD)的最小显著性变化值(least significant change,LSC),并探讨其临床应用价值。方法 4名技术员(A、B、C和D)使用GE Lunar Prodigy型双能X线骨密度仪均分别测量31名受检者(共124名)的腰椎和髋部的BMD,每位受检者连续测量2次,计算其精密度误差(precision error,PE)和LSC。结果 (1)不同技术员测量各部位BMD的各指标水平有差异,同一技术员每个测量位点的PE和LSC也不同;腰椎的PE和LSC较双侧股骨的波动幅度小,本实验中4位技术员之间对于L1～4,左、右股骨颈和左、右全髋部测量的PE变异系数(coefficient of variation,CV)差异皆无统计学意义(P0.05);(2)本团队测量L1～4的PE为:RMS-SD=0.011 g/cm~2、RMS-CV=0.011,LSC为:LSC-SD=0.031 g/cm~2、LSC-CV=0.031;左全髋的PE为:RMS-SD=0.013 g/cm~2、RMS-CV=0.014,LSC为:LSC-SD=0.036 g/cm~2、LSC-CV=0.039,右全髋的PE为:RMS-SD=0.010 g/cm~2、RMS-CV=0.011,LSC为:LSC-SD=0.026 g/cm~2、LSC-CV=0.030。结论使用DXA测量骨密度的PE小、精密度高;预计随访间隔时间(monitoring time interval,MTI)应随着感兴趣区PE的增加而延长,随着预计BMD年变化的增加而缩短。     

Evaluation of dual-energy X-ray absorptiometry bone mineral measurement—comparison of a single-beam and fan-beam design: The effect of osteophytic calcification on spine bone mineral density

Dual energy X-ray absorptiometry (DXA) using a single-beam (SB) design is a well-established procedure for measuring bone mineral area density (BMD). Recently, fan beam (FB) techniques have become available to measure BMD. We evaluated the QDR1000 and QDR2000 densitometers with regard to precision and cross-compared values using single beam (SB) and FB techniques. To study the effect of osteoarthritic changes on bone measurement (BMC in g) and bone mineral area density (BMD in g/cm²), both parameters were measured in patients with and without osteophytic calcifications (OC) of the lumbar spine. Precision errors for BMD in vitro over 1 and 6 months using the QDR2000 were 0.4% and 0.6% for SB and 0.5% and 0.7% for the three FB modes. For QDR1000 only SB is available. Using this scan mode, the BMD difference (=0.1%) in vitro between QDR1000 and QDR2000 was not significant. The short-term (same day) reproducibility of BMD in vivo was 0.85% for SB mode and 1.1% for FB scan mode (n=33). The midterm (1 month) precision errors were 0.9% for SB and 1.5% for FB (n=11). The spine BMD of 751 patients from our outpatient clinic and department of rheumatology was 1.7% lower with FB than with SB (0.878±0.137 versus 0.888±0.146 g/cm²). Lower (1.8%) BMD values were also found in the hip with FB compared to SB (0.805±0.111 versus 0.821±0.111 g/cm²). There was a highly significant (P<0.00001) correlation between SB and FB on the spine (r =0.99) and hip (r=0.98) using the QDR2000. Correlations found QDR1000 and QDR2000 were lower on the spine (r=0.97) hip (r=0.93). In contrast to hip BMD, spine BMD was significantly higher in women (n=78) with OC (FB: 0.894±0.134 g/cm², SB: 0.900±0.140 g/cm²) than in normals (n=148) (FB: 0.844±0.130 g/cm², SB: 0.865±0.140 mals (n=148) (FB: 0.844±0.130 g/cm², SB: 0.865±0.140 g/cm²) (P<0.05). The FB mode provides reproducible data in vitro and in vivo, though not as precise as SB. FB results in vivo are 1–2% lower than FB results, even with identical results in vitro. Women with OC present with higher BMD values in spine scans than normals.     

Some Physical and Clinical Factors Influencing the Measurement of Precision Error,Least Significant Change,and Bone Mineral Density in Dual-Energy X-Ray Absorptiometry

Dual-energy X-ray absorptiometry (DXA) is the standard method of measuring bone mineral density (BMD) at highly trabecular bone, which can be statistically linked to the risk of fracture. For DXA, precision error (PE) and phantom-based accuracy studies are among the most important routine quality control procedures. A precision study was performed at our institution using International Society for Clinical Densitometry guidelines. Comparing our results with those reported by other investigators, we draw the following general conclusions: the PE was higher for the spine than the hip, which we attribute to the better geometric reproducibility at the hip. The hypothesis that the DXA calculates BMD relative to water was validated. Whether follow-up measurements are performed by the same technologist on the same day—or different technologists on subsequent days—does not appear to have a clinically significant impact on PE or least significant change (LSC). Mixing beam types (i.e., fan and pencil) may affect lumbar PE and LSC measurements more significantly than those of the hip. The use of a single technologist may reduce the PE for the lumbar spine but appears to increase it for the hip. Restricting the patient population to the female gender has the apparent effect of narrowing the gap between lumbar and hip PEs. Finally, the degree of BMD measurement accuracy can be affected by the type of phantom being used (e.g., European Spine Phantom vs Lunar phantom) and the faults in specific DXA edge detection algorithms.     

Cross-Calibration of Prodigy and Horizon A Densitometers and Precision of the Horizon A Densitometer

We performed this study to enable a reliable transition for clinical study participants and patients from a GE Lunar Prodigy to a Hologic Horizon A dual-energy X-ray absorptiometry (DXA) scanner and to assess the reproducibility of measurements made on the new DXA scanner. Forty-five older adults had one spine, hip, and total body scan on a Prodigy dual-energy X-ray absorptiometry (DXA) scanner and 2 spine, hip, and total body scans, with repositioning, on a new Hologic Horizon A DXA scanner. Linear regression models were used to derive cross calibration equations for each measure on the 2 scanners. Precision (group root-mean-square average coefficient of variation) of bone mineral density (BMD) of the total hip, femoral neck, and lumbar spine (L1-L4), and total body fat, bone, and lean mass, appendicular lean mass, and trabecular bone score (TBS) was assessed using the International Society of Clinical Densitometry's (ISCD's) Advanced Precision Calculation Tool. Correlation coefficients for the BMD and body composition measures on the 2 scanners ranged from 0.94 to 0.99 (p<0.001). When compared with values on the Prodigy, mean BMD on the Horizon A was lower at each skeletal site (0.136 g/cm² lower at the femoral neck and 0.169 g/cm² lower at the lumbar spine (L1-4)), fat mass was 0.47 kg lower, and lean mass was 4.50 kg higher. Precision of the Horizon A scans was 1.60% for total hip, 1.94% for femoral neck, and 1.25% for spine (L1-4) BMD. Precision of TBS was 1.67%. Precision of total body fat mass was 2.16%, total body lean mass was 1.26%, appendicular lean mass was 1.97%, and total body bone mass was 1.12%. The differences in BMD and body composition values on the 2 scanners illustrate the importance of cross-calibration to account for these differences when transitioning clinical study participants and patients from one scanner to another.     

Differential effects of estrogen treatment on bone mineral density of the spine,hip, wrist and total body in late postmenopausal women

It is commonly believed that estrogen is effective only in preventing menopause-related loss of bone mineral. However, recent studies found significant increases in bone mineral density (BMD) of the spine in response to estrogen, particularly in older women. The degree to which estrogen can restore BMD of the hip is uncertain. In the present study, changes in BMD of the lumber spine (L2–4), hip (neck, trochanter and Ward's triangle), wrist (ultradistal) and total body in response to 1 year of hormone replacement therapy (HRT) were evaluated by dual-energy X-ray absorptiometry (DXA) in women 10 or more years past menopause. Twelve women, aged 61–74 years, received conjugated estrogens 0.625 mg and cyclic medroxyprogesterone acetate 5 mg; 12 women who did not receive HRT were controls. Calcium intake was adjusted to approximately 1500 mg/day in all subjects. There were no differences between the groups in BMD prior to treatment. Increases in BMD of the lumbar spine (mean±SD, 0.041±0.030 g/cm²), hip (neck, 0.019±0.018 g/cm²; trochanter, 0.017±0.012 g/cm²; Ward's triangle, 0.026±0.029 g/cm²) and total body (0.013±0.016 g/cm²) occurred in response to HRT, and these changes were significantly different from those in controls (spine, 0.005±0.020 g/cm²; neck, –0.007±0.026 g/cm²; trochanter, 0.002±0.014 g/cm²; Ward's triangle, 0.003±0.019 g/cm²; total body, –0.001±0.017 g/cm²). HRT appears to be most effective at weight-bearing sites that have a high cancellous bone content. This study demonstrates that HRT significantly increases bone mass of the lumbar spine and proximal femur in osteopenic, late postmenopausal women, and may, therefore, be effective in preventing osteoporotic fractures at these sites in this population.     

In Vivo Precision of the GE Lunar iDXA for the Assessment of Lumbar Spine,Total Hip,Femoral Neck,and Total Body Bone Mineral Density in Severely Obese Patients

No study has evaluated the precision of the GE Lunar iDXATM (GE Healthcare) in measuring bone mineral density (BMD) among severely obese patients. The purpose of the study was to evaluate the precision of the GE Lunar iDXATM for assessing BMD, including the lumbar spine L1–L4, L2–L4, the total hip, femoral neck, and total body in a severely obese population (body mass index [BMI] > 40 kg/m²). Sixty-four severely obese participants with a mean age of 46 ± 11 yr, BMI of 49 ± 6 kg/m², and a mean body mass of 136.8 ± 20.4 kg took part in this investigation. Two consecutive iDXA scans (with repositioning) of the total body (total body BMD [TBBMD]), lumbar spine (L1–L4 and L2–L4), total hip (total hip BMD [THBMD]), and femoral neck (femoral neck BMD [FNBMD]) were conducted for each participant. The coefficient of variation (CV), the root mean square (RMS) averages of standard deviations of repeated measurements, the corresponding 95% least significant change, and intraclass correlations (ICCs) were calculated. In addition, analysis of bias and coefficients of repeatability were calculated. The results showed a high level of precision for total body (TBBMD), lumbar spine (L1–L4), and total hip (THBMD) with values of RMS: 0.013, 0.014, and 0.011 g/cm²; CV: 0.97%, 1.05%, and 0.99%, respectively. Precision error for the femoral neck was 2.34% (RMS: 0.025 g/cm²) but still represented high reproducibility. ICCs in all dual-energy X-ray absorptiometry measurements were 0.99 with FNBMD having the lowest at 0.98. Coefficients of repeatability for THBMD, FNBMD, L1–L4, L2–L4, and TBBMD were 0.0312, 0.0688, 0.0383, 0.0493, and 0.0312 g/cm², respectively. The Lunar iDXA demonstrated excellent precision for BMD measurements and is the first study to assess reproducibility of the GE Lunar iDXA with severely obese adults.     

Establishing a Total Hip T-Score Threshold to Measure Contralateral Hip Bone Mineral Density: Avoiding Missed Diagnosis of Osteoporosis

Bone mineral density (BMD) of the hip is routinely measured unilaterally, but can differ between left and right. This study aimed to establish total hip T-score thresholds for measuring contralateral hip BMD, to avoid missing the diagnosis of osteoporosis. In 4914 participants (2709 females) in the Busselton Healthy Ageing Study, BMD of both hips and lumbar spine (L1–L4) was measured by dual-energy x-ray absorptiometry (DXA) using a GE Lunar Prodigy Pro densitometer. Least significant change (LSC) was calculated according to International Society for Clinical Densitometry recommendations. For participants whose left-right total hip BMD difference exceeded LSC, the 95th percentile of the difference in T-score was calculated, then added to ?2.5 (the cut-off for osteoporosis) to derive T-score thresholds for measuring contralateral hip to avoid a missed diagnosis in 95% of individuals. Participant mean age (±SD) was 57.4 ± 5.8 years; total hip T-score was 0.7 ± 0.1 in males and ?0.2 ± 1.1 in females. Left and right total hip BMD were highly correlated (r = 0.943 for males, 0.959 for females), but in 56.2% of males and 50.0% of females, the left-right difference exceeded the LSC of 0.026 g/cm². In these participants, the 95th percentile of difference in T-score between two hips was 0.872 in males and 0.742 in females. This gave T-score thresholds for measuring contralateral total hip BMD of ?1.6 (males) and ?1.8 (females). When total hip T-score is between ?1.6 and ?2.5 (males), or between ?1.8 and ?2.5 (females), measuring contralateral hip BMD could avoid a missed diagnosis of osteoporosis.     

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.     

Densitometry of the radius using single and dual energy absorptiometry

Though spinal and femoral measurements are typically preferred for evaluating skeletal density, an abundance of forearm data exists, primarily from single photon absorptiometry (SPA) devices. Most dual X-ray absorptiometry (DXA) scanners are capable of scanning the forearm and provide analysis tools to duplicate conventional SPA measurements. In this study, we have compared the radius density measurements from three commonly available densitometers: a Norland 278 SPA, a Lunar DPX-L, and a Hologic 1000/W. Radius bone mineral density (BMD) on the nondominant forearm was measured in 28 volunteers (21 women and 7 men) aged 24–78, with an average age of 51±17 years. Values were compared and regression relationships derived at corresponding measurement sites. SPA and DXA BMD values were found to be highly correlated (r=0.99) with small standard errors (0.014 g/cm²–0.021 g/cm²), though significant absolute differences were observed at most measurement regions. Correlation slopes ranged from 0.85 to 1.04, with intercepts from 0.01 to 0.08 g/cm². Using the resultant regression equations, SPA BMD values can be converted to DXA values with an expected error of roughly 3%. DXA BMD can also be interconverted between Lunar and Hologic with a similar expected error. In situations where this level of imprecision is acceptable, patient forearm measurements obtained on different systems can be interconverted.     

Follow-up of Individual Patients on Two DXA Scanners of the Same Manufacturer

Measuring and monitoring changes in bone mineral density (BMD) is usually done by dual-energy X-ray absorptiometry (DXA). Replacement of old devices is becoming increasingly frequent. To cross-calibrate two Hologic devices, a QDR 1000 and a QDR 4500A, we measured three phantoms – a Hologic spine phantom, a Hologic block phantom (without and with subregions analysis) and a European Spine Phantom – 20 times each without repositioning on both devices. The mean difference between BMD obtained on the two devices was 0.003, 0.033, 0.051 and −0.045 g/cm² respectively. We also measured the spine and hip of 60 women aged 19–78 years twice on the same day on both devices. Another group of 30 women aged 52–83 years were measured twice on the QDR 4500 A device (15 days apart). We analyzed the data using Pearson’s correlation coefficient, and Bland and Altman’s method, and calculated the smallest detectable difference (SDD). Results on the two devices were highly correlated: r ²= 0.99, 0.95, 0.96 for spine, femoral neck and total hip BMD respectively. SDD was higher for scans done on different devices than for those done twice on the same device: the SDDs were 0.048, 0.046 and 0.047 g/cm² for spine, femoral neck and total hip BMD respectively measured on two different devices, while the equivalent values were 0.034, 0.036 and 0.027 g/cm² using a single device. The difference in BMD results was not dependent on BMD. Our results suggest that, although devices are properly cross-calibrated, differences among them great enough to be clinically relevant can be observed in vivo. Received: 30 June 1999 / Accepted: 7 February 2000     

Minimum sample size requirements for bone density precision assessment produce inconsistency in clinical monitoring

Introduction Detection of change during bone mineral density (BMD) monitoring is affected by test precision. The International Society of Clinical Densitometry (ISCD) recommends that each center determine precision error using repeat measurements in 30 subjects (or an equivalent method providing 30 degrees of freedom).Methods We hypothesized that this sample size may be too small for a robust precision estimate, which could affect the performance of BMD monitoring in clinical practice. Replicate measurements of the spine and total hip (198 spine and 193 hip scan pairs) were obtained (interval 6±5 days). The sample was randomly divided into six groups of 30 patients each. Root mean square standard deviation (RMS-SD in g/cm²) and coefficient of variation (RMS-CV in %) precision errors and corresponding 95% least significant change (LSC) were calculated for each group and the pooled sample. LSC cutoffs were applied to 1,420 individuals from the Manitoba Bone Density Program who had follow-up measurements on the same instrument (interval 21±9 months). While the pooled spine RMS-SD was 0.017 and pooled hip RMS-SD was 0.009 g/cm², sample sizes of 30 gave a range of RMS-SD point estimates from 0.012 to 0.021 for the spine and from 0.008 to 0.012 for the hip.Results When the respective LSC cutoffs were applied to the 1,420 follow-up scan pairs, the fraction of patients categorized with significant change in the spine varied from 20.7% to 46.0%; four of the six LSCs based upon 30 subjects gave fractions significantly different from the pooled LSC of 30.7%. Significant change fractions for the hip varied from 31.1% to 51.1%; two of the six LSCs based upon 30 subjects gave fractions significantly different from the pooled LSC of 40.1%. Similar results were obtained using relative precision errors.Conclusion BMD precision studies using a sample size of 30 are insufficient to reliably characterize precision error or change during clinical monitoring.     

Factors Affecting Short‐Term Bone Density Precision Assessment and the Effect on Patient Monitoring

The most widely used procedure for performing a BMD reproducibility assessment (same‐technologist with simple repositioning on the same day) systematically underestimates precision error and will lead to over categorization of change in a large fraction of monitored patients. Introduction: The most common procedure for establishing the least significant change (LSC) to monitor bone mineral density (BMD) with DXA is for the same technologist to perform repeat subject scans on the same day with simple repositioning. The objective of the current report is to determine how the reproducibility scanning procedure impacts on the precision assessment and categorization of change in routine clinical practice. Materials and Methods: The study population was drawn from the database of the Manitoba Bone Density Program which includes all clinical DXA test results for the Province of Manitoba, Canada. All patients who had baseline and follow up total spine (L1–4) and the total hip BMD measurements on the same instrument up to March 31, 2007 were included as the ‘clinical monitoring population’ (N = 5048 scan‐pairs). BMD precision was assessed in a convenience sample of patients who were agreeable to undergoing a repeat assessment (50% performed on the same day with repositioning, 68% by different technologists) (N = 331 spine and 328 hip scan‐pairs). Results: Precision error was greater when the scan‐pairs were acquired on different days than on the same day for both the total spine (p < .001) and total hip (p < .01). No other factor was consistently associated with precision error. The reference LSC (different days and different technologists) categorized the smallest fraction of the monitored population with change, whereas other combinations gave a significant rate of over categorization (up to 19.3% for the lumbar spine and up to 18.3% for the total hip). Conclusions: The most widely procedure for performing a BMD reproducibility assessment (same‐technologist with simple repositioning on the same day) systematically underestimates precision error and will lead to over categorization of change in a large fraction of monitored patients.     

Simulated increases in body fat and errors in bone mineral density measurements by DXA and QCT

Major alterations in body composition, such as with obesity and weight loss, have complex effects on the measurement of bone mineral density (BMD) by dual‐energy X‐ray absorptiometry (DXA). The effects of altered body fat on quantitative computed tomography (QCT) measurements are unknown. We scanned a spine phantom by DXA and QCT before and after surrounding with sequential fat layers (up to 12 kg). In addition, we measured lumbar spine and proximal femur BMD by DXA and trabecular spine BMD by QCT in 13 adult volunteers before and after a simulated 7.5 kg increase in body fat. With the spine phantom, DXA BMD increased linearly with sequential fat layering at the normal (p < 0.01) and osteopenic (p < 0.01) levels, but QCT BMD did not change significantly. In humans, fat layering significantly reduced DXA spine BMD values (mean ± SD: ?2.2 ± 3.7%, p = 0.05) and increased the variability of measurements. In contrast, fat layering increased QCT spine BMD in humans (mean ± SD: 1.5 ± 2.5%, p = 0.05). Fat layering did not change mean DXA BMD of the femoral neck or total hip in humans significantly, but measurements became less precise. Associations between baseline and fat‐simulation scans were stronger for QCT of the spine (r² = 0.97) than for DXA of the spine (r² = 0.87), total hip (r² = 0.80), or femoral neck (r² = 0.75). Bland‐Altman plots revealed that fat‐associated errors were greater for DXA spine and hip BMD than for QCT trabecular spine BMD. Fat layering introduces error and decreases the reproducibility of DXA spine and hip BMD measurements in human volunteers. Although overlying fat also affects QCT BMD measurements, the error is smaller and more uniform than with DXA BMD. Caution must be used when interpreting BMD changes in humans whose body composition is changing. © 2012 American Society for Bone and Mineral Research     

Dual X-ray Absorptiometry

The DMS Lexxos is the first cone-beam dual X-ray absorptiometry (DXA) system capable of performing bone mineral density (BMD) measurements of the spine and hip. By using a two-dimensional (2-D) detector array rather than the linear array used with conventional fan-beam DXA systems, image acquisition time on Lexxos is only 1.5 s. However, the need to correct for the large signal from scattered radiation reaching the detector is a potential source of error in cone-beam DXA. The aim of this clinical evaluation of the Lexxos bone densitometer was to investigate the relative accuracy of cone-beam BMD measurements compared with conventional DXA by performing an in vivo cross-calibration study with an established fan-beam system, the Hologic QDR-4500. Spine (L1–L4) and hip BMD measurements were performed in 135 patients (111 women, 24 men) referred for a bone densitometry examination. Duplicate Lexxos measurements were performed in 27 female patients to evaluate precision. On average, Lexxos spine and femoral neck BMD measurements were 2% lower than those on the QDR-4500, whereas total hip BMD was 5% higher. Larger differences were found for the trochanter and Wards triangle regions. For all sites, Lexxos BMD measurements showed a strong linear relationship with those measured on the QDR-4500 with correlation coefficients in the range r = 0.95 to 0.97 for the clinically important spine, femoral neck, and total hip regions. The root mean standard error (RMSE) between Lexxos and QDR-4500 BMDs ranged from 0.037 g/cm² for the femoral neck to 0.060 g/cm² for the spine, whereas Lexxos precision was 1.3% for total hip, 2.0% for femoral neck, and 2.3% for spine BMD. Although for the hip BMD sites the RMSE and precision of Lexxos measurements were similar to studies of pencil-beam and fan-beam DXA systems, the results for the spine were poorer than expected. The findings of this study suggest that Lexxos corrects accurately for the effects of scattered radiation at the detector, but that the precision of spine BMD measurements may be limited by involuntary patient movement between the high and low energy X-ray exposures.     

Is a Fixed Value for the Least Significant Change Appropriate?

The least significant change (LSC) represents the smallest difference between successive measurements of bone mineral density (BMD) that can be considered to be a real change and not attributable to chance. The LSC is derived from same-day in vivo BMD precision measurements. Our first objective was to determine if the LSC differs between technologists. Our second objective was to determine if patient body size influenced the LSC. Each of 8 technologists measured same-day precision in groups of 30 patients for the lumbar spine and the total trochanter and neck regions of the proximal femur. At the spine, precision ranged from 0.008 to 0.011 g/cm² and did not differ between technologists. Precision for the total region of the left proximal femur ranged from 0.006 to 0.016 g/cm² and did differ between technologists. For the trochanter and neck regions, precision ranged from 0.008 to 0.013 g/cm² for the former and from 0.010 to 0.020 g/cm² for the latter, again, with inter-technologist differences. The LSC for the lumbar spine increased linearly from 0.022 to 0.031 g/cm² when body mass index (BMI) increased from 19.5 to 31.3 kg/m². In contrast, there was no discernable impact of BMI on the LSC for any of the proximal femur regions. The LSC at the spine is determined by the patient, whereas the LSC at the femur is determined by the technologist. Use of a single value for the LSC will lead to misinterpretations of the significance of BMD changes at both the spine and the proximal femur.     

唑来膦酸对骨质疏松性股骨转子间骨折作用效果分析

 目的 比较应用唑来膦酸与降钙素对老年骨质疏松性股骨转子间骨折疗效的影响。方法 回顾性分析 2009年6月到2012年11月,采用闭合复位髓内钉固定术治疗610例骨质疏松性转子间骨折患者资料,按照入院顺序及是否获得完整随访资料将543例患者分为两组。其中降钙素组325例,2009年6月至2011年4月手术,男107例,女218例; 年龄(75.02±5.65)岁;Evans?Jensen分型：Ⅰ型87例,Ⅱ型136例,Ⅲ型102例;腰椎骨密度平均(0.737±0.08) g/cm²,髋部平均 (0.725±0.05)g/cm²;应用降钙素等治疗。唑来膦酸组218例,2011年5月至2012年11月手术,男82例,女136例; 年龄(74.71±5.32)岁;Evans?Jensen分型：Ⅰ型62例,Ⅱ型91例,Ⅲ型65例;腰椎骨密度平均为(0.738±0.05)g/cm²,髋部平均为(0.722±0.06)g/cm²;术后7d内使用唑来膦酸治疗。两组患者分别比较住院期间及术后1年骨密度值。采用Harris评分、视觉模拟评分(visual analogue score, VAS)评价髋关节功能和疼痛程度。结果 降钙素组随访时间为5～22个月,平均 12.8个月;唑来膦酸组随访时间为4～19个月,平均12.5个月。患者影像学骨折愈合时间、Harris评分、VAS评分,唑来膦酸组分别为(14.25±1.38)周、(68.88±5.71)分、(0.36±0.55)分;降钙素组分别为(14.39±1.12)周、(69.47±4.60)分、(0.33± 0.48)分;两组各指标比较,差异无统计学意义。术后1年唑来膦酸组腰椎骨密度平均为(0.76±0.06)g/cm²,髋部平均为 (0.75±0.04)g/cm²,降钙素组腰椎骨密度平均为(0.75±0.07)g/cm²,髋部平均为(0.74±0.07) g/cm²。唑来膦酸组患者术后1 年与术前骨密度比较差异有统计学意义。术后1年,两组骨密度比较,差异有统计学意义。结论 老年骨质疏松性股骨 转子间骨折内固定术后应用唑来膦酸未对骨折愈合和髋关节功能恢复造成影响,术后1年骨密度明显升高。     

Variations in diagnostic performances of dual-energy X-ray absorptiometry in the northwest of The Netherlands

Between-center variation in bone densitometry may influence the frequency of the diagnosis of osteoporosis. To evaluate this problem, dual-energy X-ray absorptiometry (DXA) machines of the medical centers in the northwest of The Netherlands were evaluated. Four phantoms were used to test the 17 DXA machines of 16 participating centers. Each phantom was measured 10 times and the data were analyzed on the corresponding DXA machine using the software delivered by the manufacturer. The analyses were done with the reference population as used in daily practice. There were DXA devices of seven different brands and types, using four different reference populations for the lumbar spine and seven for the hip. The observed differences in bone mineral densities (BMD) were up to 0.20 g/cm² for the lumbar spine, 0.15 g/cm² for the femoral neck, and 0.12 g/cm² for the total hip. The coefficients of variation (CV) of the repeated phantom measurements ranged between 0.3% and 1.3% for the lumbar spine, 1.6% and 4.6% for the femoral neck, and 0.3% and 0.9% for the total hip. The mean female T-scores of 10 phantom measurements differed up to 0.6 SD between the DXA machines for the lumbar spine and up to 0.8 SD for the total hip. Mathematically, replacing a Hologic 2000 DXA machine with a newer type of the same brand (a Hologic 4500) caused a shift in diagnosis from osteoporosis to osteopenia of +1.1% for the lumbar spine and –4.5% for the total hip. When the Hologic 2000 was replaced by a Hologic 4500 with NHANES reference values, the shift from osteoporosis to osteopenia was also +1.1% for the lumbar spine, and –13.4% for the total hip. The clinical impact of the observed differences is difficult to estimate. One may conclude that the differences of the tested DXA devices are partly based on differences in DXA machines, but for the most part on the use of different reference populations. It is recommended to standardize the reference population, although the consequent shift in diagnosis will be confusing for physicians and patients, and adaptation of the reference values on the DXA devices of different brands with different technical qualities and measurement specifications will be difficult.     

Prediction of incident osteoporotic fractures in elderly women using the free estradiol index

A decline in postmenopausal estrogen concentration accelerates postmenopausal bone loss. We have examined the predictive power of endogenous estrogen production, DXA hip bone density (BMD), and heel quantitative ultrasound (QUS) on incident clinical fracture in a prospective 3-year population based, randomised controlled trial of calcium supplementation. Baseline blood testing on 1499 women mean (SD) age 75 (3) years for estradiol and sex hormone binding globulin measurements and ankle QUS measurements (Lunar Achilles) was undertaken. Bone density was measured using DXA (Hologic 4500A) at 1 year. Incident clinical fractures were confirmed by X-ray. At 3 years, 10% had sustained more than one incident fracture. The fracture group had significantly lower levels of free estradiol index (FEI) (0.40±0.44 versus 0.49±0.54 pmol/nmol), hip BMD (0.776±0.129 versus 0.815±0.124 g/cm²) and measures of QUS (BUA 98±8 versus 101±8 db/Hz, SOS 1504±22 versus 1514 ±26 m/s; stiffness 67±11 versus 71±11 % mean young adult), respectively, than the non-fracture group. After adjustment for age, weight, use of topical estrogen, calcium supplementation and prevalent fracture, incident fracture was predicted by free estradiol index (HR per SD: 1.43:95%CI: 1.08–1.91, P=0.013). After adjustment for BMD, SOS or stiffness, the free estradiol index no longer predicted fracture. When examined separately, the presence of a vertebral or an appendicular fracture was associated with an 18% lower free estradiol index compared with no fracture. The risk of vertebral fracture increased with decreased free estradiol index (HR per SD reduction: 1.63:95% CI: 0.91–2.92); the risk of appendicular fracture also increased with decreased free estradiol index (HR per SD reduction: 1.45:95% CI: 1.05–2.01) after adjustment for age, weight, use of topical estrogen, calcium supplementation and prevalent fracture. After further adjustment for hip BMD or QUS measures, the effect of free estradiol index was no longer significant for vertebral or appendicular fractures. Therefore, a low free estradiol index increases the probability of having an incident fracture as a result of decreased BMD. These data confirm the importance of postmenopausal estrogen concentration in the pathogenesis of osteoporosis in elderly women.     

Dual-energy X-ray absorptiometry of human metatarsals: Precision,least significant change and association to ex vivo fracture force

BackgroundFractures are common in foot bones, but clinicians lack adequate indices of bone strength.ObjectivesWe used dual-energy X-ray absorptiometry (DXA) to measure bone mineral density (BMD) and content (BMC) of excised human metatarsals, determined intra- and inter-rater measurement precision, and assessed associations between BMD/BMC and ex vivo bone fracture strength.MethodsTwo raters each made two measurements of whole-bone and sub-regional BMD and BMC in both second and third metatarsals from 10 cadavers. Variance components analysis was used to assess variability attributable to repeat measurements, raters, sub-regions, bones, sides, and cadavers. Root-mean-square standard deviation (RMS-SD) and least-significant change (LSC) were used to assess rater precision and ultimate forces during 3-point bending were tested for correlations with BMD and BMC.ResultsVariation due to repeat measurements and rater was low (<1% combined) for BMD and BMC. RMS-SD for whole metatarsal BMD of both metatarsals ranged from 0.004 to 0.010 g/cm² and 0.062 to 0.086 g for BMC. Whole metatarsal and sub-region BMD and BMC were strongly correlated to ex vivo fracture force (r² = 0.67–0.93).ConclusionsDXA measurements of BMD and BMC have high intra- and inter-rater precision and are strongly correlated to ex vivo bone strength.