Effect of femoral rotation on bone mineral density measurements with dual energy X-ray absorptiometry

Precision in femoral neck scans with dual energy X-ray absorptiometry (DXA) is affected by variability in positioning and subsequent repositioning of the femur for repeated scans. To study the in vitro effect of femoral rotation on the bone mineral density (BMD), four fresh-frozen cadaveric femurs were fixed in a specially designed jig which allows for rotation of the femurs. BMD measurements of the femurs were done in neutral position (0°) i.e., with the femoral neck axis parallel to the surface of the couch and at 15°, 30°, and 45° of internal and external rotation. In vivo precision of the femoral neck scan was determined in five normal male subjects. The scans were first done with the legs positioned using the manufacturer's foot block. Five scans were performed, with repositioning, on the left hip of each subject. The procedure was then repeated with the legs positioned using a custom-designed positioning jig to minimize the rotation of the hips during a scan. In the in vitro study, the femoral neck BMD value was minimum at neutral position (0°) and increased when the femur was rotated internally or externally. In vivo precision error of the femoral neck scan was reduced by almost 50% with the use of the positioning jig when compared with the manufacturer's foot block. Femoral rotation was shown to have a significant effect on BMD measurements, and proper positioning of the femur during a scan can improve precision significantly.     

Clinical reproducibility of dual energy X-ray absorptiometry

Dual energy x-ray absorptiometry is a technique advocated for the measurement of bone mass throughout the skeleton, and recently it has been used to measure changes in periprosthetic bone mass after joint replacement. The accuracy and precision of the method in clinical patient populations have not been firmly established. This study sought to establish the short-term reproductibility of measurements made with dual energy x-ray absorptiometry of multiple sites in a large sample of elderly patients with rheumatic disease. Reproductibility was assessed in the lumbar spine and in three femoral sites in 69 patients participating in a longitudinal clinical trial. In each patient, absorptiometry was performed twice in the same day at as many as five time points over a 2-year period. The mean (±SD) baseline bone density was 0.783 ± 0.128 g/cm² for the femoral neck and 1.015 ± 0.218 g/cm² for the lumbar spine. The correlations between the duplicate baseline measurements of the spine were excellent (r = 0.9936, p < 0.001) and were stable over the 2-year period; the mean difference between the duplicate baseline measurements was 1.82 ± 1.54% and the mean coefficient of variation was 1.29%. Measurements in the femur were much less precise: these values were 3.61 ± 3.14% and 2.55% in the femoral neck, 3.66 ± 4.35% and 2.59% in the greater trochanter, and 5.28 ± 5.61% and 3.73% in Ward's triangle. This study evaluated the short-term reproductibility of dual energy x-ray absorptiometry in a clinical population. The reproductibility of a technique must be taken into account when it is applied longitudinally to follow patients over time. The reproductibility of bone densitometry of the spine in large clinical populations with orthopaedic and rheumatic disease was similar to that reported for in vitro measurements and for very small sample studies of healthy normal subjects. However, the reproductibility of densitometry of femoral sites was much poorer than that for spinal sites. Reproducibility is a significant methodological issue for the use of dual energy x-ray absorptiometry to assess the effect of osteoporosis therapies on the hip as well as the change in periprosthetic bone mass around a hip prosthesis. The poorer reproductibility of the measurements in the femoral sites suggests that a much wider margin of error is required in the interpretation of within-patient change in bone mass over time.     

定量超声和双能X线骨密度测定诊断骨质疏松的比较

目的通过对同一个人的跟骨超声强度（STI）测量与双能X线吸收法（DEXA）测量腰2-4、股骨近端骨密度（BMD）的临床对比,评价定量超声骨质测量仪（QUS）跟骨STI的测量,对诊断骨质疏松（OP）的敏感性和与DEXA测量BMD的相关性.方法对3266名20～89岁健康人群同时采用DEXA测量L2-4、右股骨近端（Neck、Ward、Troch）BMD和QUS测量右跟骨STI值进行相关分析.结果峰值骨量男性STI与BMD均出现在20～29岁,女性STI出现在20～29岁,BMD则出现在30～39岁;随年龄的增加腰椎、股骨近端BMD及超声强度均下降,女性在50岁后,男性在70岁后有个显著下降过程;OP检出率两种仪器无明显差异.在健康人中BMD与STI的相关系数（R=0.21-0.26）,骨质疏松患者BMD与STI的相关系数（R=0.14-0.24）.结论DEXA测量的BMD与QUS测量的STI无相关关系.这表明QUS主要测量骨的结构,而DEXA则是测量骨量的变化,两者相辅相承,共同测量能更好地监测骨质疏松、预测OP性骨折的发生.     

Osteodensitometry measurements of periprosthetic bone using dual energy X-ray absorptiometry following total knee arthroplasty

Introduction

The present study investigates the reaction of bone density as well as the possible factors influencing this reaction following a cement-free total knee arthroplasty (TKA).

Materials and methods

Osteodensitometry scan data from 50 prospective patients with TKA was evaluated. The patients were split into two groups according to the number of follow-up investigations undertaken. No patient included in the study had received medication to increase bone density. To identify the changes in periprosthetic bone density, dual energy X-ray absorptiometry (DXA) bone density measurements in defined regions of interest (ROI) were performed over a period of 24?months postoperative. The test parameters included gender, severity of arthrosis, as well as the metric parameters T-score, body mass index, cortical bone marrow index, and the varus alignment for the respective patient.

Results

The most significant changes in bone density were recorded within the first 3?months postoperative, in particular, the highest bone density loss was found in the region of the proximal medial tibia. Moreover, significant gender-specific associations regarding changes in bone density were established.

Conclusion

Finally, results achieved in the present study demonstrate that the fundamental classification in defined ROI proved to be functional and effective.     

Bone mineral and soft tissue measurements by dual-energy X-ray absorptiometry during growth

There have been several previous compilations of reference ranges of total body bone mineral measured by dual-energy X-ray absorptiometry (DXA) in children and young adults during growth, but little attempt to compare the results or to consider differences arising from the use of instruments from different manufacturers. We measured bone mineral and soft tissue in 216 girls, aged 11-17 years, using a Hologic scanner. Our results were compared with those from four other studies, all performed on white subjects, but in different countries, and including measurements performed with Hologic, Lunar, and Norland scanners. The general pattern of bone growth with age was very similar in all the studies. Quantitative differences could largely be accounted for by known differences of calibration of DXA scanners from the different manufacturers. When bone mass was plotted against lean or total mass instead of age there were also close similarities. An apparent difference between boys and girls in one study was shown to be due to differences in soft tissue composition, rather than different patterns of bone growth. Conclusions from this apparent difference concerning the effect of estrogen at puberty were shown to be unwarranted.     

Role of dual energy X-ray absorptiometry in monitoring fracture healing in a rat femoral fracture model

Earlymobilizationandweightbearingplayimportantrolesinminimizingtheamountofbonelosstoachievegoodhealingafterbonefracture.1Areliableandnoninvasivemethodforevaluatingfracturehealingcannotonlyhelpdecidewhentostarweightbearing, butalsohelpdetecttheimpairedboneunionearlytopreventdelayedunionsornonunions.However, objectivequantitativemethodsforearlyevaluationoffracturehealinghavenotbeendevelopedyet. DualenergyX rayabsorptiometry(DEXA)isoneofthemostaccuratemethodsformeasuringbonemassinvivo. Itismain…     

The usefulness of dual energy X-ray and laser absorptiometry of the calcaneus versus dual energy X-ray absorptiometry of hip and spine in diagnosing manifest osteoporosis

Introduction  Osteoporosis is a major health problem. Dual energy X-ray absorptiometry (DXA) of the hip and spine is the worldwide standard in diagnosing osteoporosis. Measurement of bone mineral density (BMD) with dual energy X-ray and laser absorptiometry of the calcaneus (Calscan) might be a good alternative. Advantages of the Calscan are that it is quick, widely available and manageable. In this study we compared BMD expressed in T-scores measured by DXA and Calscan. The aim of this study was to define threshold T-scores on the Calscan that could exclude or predict osteoporosis correctly in comparison with DXA. Materials and methods  Patients ≥50 years attending our emergency department with a fracture were offered osteoporosis screening at our fracture and osteoporosis outpatient clinic (FO-Clinic) and enrolled in this study. BMD was measured at the hip and spine using DXA and at the calcaneus using Calscan. A T-score measured by DXA ≤−2 standard deviations (SD) below the reference population was defined as manifest osteoporosis and was the treatment threshold. Results  During a 10-month study period, 182 patients were screened with both devices. The mean DXA-T-score was −1.63 SD (range −4.9 to 2.1) and Calscan T-score −1.91 SD (range −5.3 to 1.4). There was a significant correlation between both devices (r = 0.47, P < 0.01). Using an upper threshold for the Calscan T-score of −1.3 SD, 47 patients could be classified as non-osteoporotic with 89.3% sensitivity (95% CI 80.0–95.3%). Using a lower threshold for the Calscan T-score of −2.9 SD, 34 patients could be classified by the Calscan as osteoporotic with 90.7% specificity (95% CI 83.5–95.4). The remaining 101 patients could only be correctly classified by DXA-T-scores. Conclusion  Although DXA is the established modality worldwide in measuring BMD it is restricted to specialized centres. Peripheral bone densitometers like the Calscan are widely available. When BMD measurements with DXA were compared to Calscan measurements it was possible to correctly classify 81 of 182 patients based on the Calscan T-score. Of these 81 patients 34 could be classified as manifest osteoporotic and 47 as non-osteoporotic. Therefore the Calscan seems to be a promising technique which might be used as a screening device at a FO-Clinic, especially when DXA is not easily available.     

Quantitative assessment of callus distraction using dual energy X-ray absorptiometry

Summary. Bone mineralisation during and after limb lengthening procedures on the femur or tibia using unilateral fixators has been monitored quantitatively using dual energy X-ray absorptiometry (DEXA). We measured the bone mineral density (BMD) prospectively in the newly formed callus, in the bone adjacent to the callus and in the proximal femur. In twenty-one patients we showed a typical course with a peak value at 4 – 6 weeks after beginning distraction and a minimum value at maximum distraction. In the consolidation period the BMD in the distraction gap increased until the fixator was removed. The BMD in the regenerated bone increased faster in the regions of interest (ROI) opposite the fixator compared to those near it. Dynamisation caused more homogeneous regeneration equalising V _BMD in the different ROIs. The BMD in the proximal femur of the leg which was operated on decreased to 67% and in the opposite leg to 87% of the preoperative value. DEXA provides a precise and quantitative assessment of callus and bone mineralisation during limb lengthening and helps in understanding what is happening during these procedures.

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Résumé. Le processus de la minéralisation peut précisément être étudié d’une manière quantitative pendant et après la distraction du cal au moyen de l’absorptiométrie en énergie-binaire (DEXA) en créant une petite radioexposition. Des patients (n = 21) avec une distraction du cal, auxquels nous avons mesuré prospectivement la densité minérale de l’os (bone mineral density = BMD) dans et autour du cal nouvellement formé, étaient traités avec des fixateurs externes unilatéraux. La minéralisation a montré une courbe typique avec une première pointe de valeur [0,365 +/– 0,196 g/cm ² (30,9% de la première valeur)] à 4 – 6 semaines après le début de la distraction. Une valeur minimale apparut à la distraction maximale. Dans la période de consolidation la BMD est montèe jusqu’au moment de l’enlèvement du fixateur à 1,020 +/– 0,234 g/cm² (87%). La minéralisation du cal, mésurée grace à la technique des ?regions of interest (ROIs)?, augmenté plus vite aux ROIs éloignées qu’aux ROIs très proches du fixateur. De la dynamisation du fixateur résulte une vitesse de minéralisation plus homogène. Nous considérons la DEXA comme une méthode précise pour étudier les processus de la minéralisation et du développement du cal pendant la distraction avec un fixateur unilatéral. En tenant compte des limites de la technique, la DEXA – qui nous livre des valeurs quantitatives – nous aide à comprendre ce qui se passe pendant la distraction.

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Accepted: 11 July 1996     

Reproducibility of lateral spine scans using dual energy X-ray absorptiometry

Summary Reproducibility of lateral spine dual energy X-ray absorptiometry (LAT DEXA) scans using a Lunar DPX-L scanner was assessed in a cadaveric phantom and in patients. One hundred phantom measurements over 7 months demonstrated a longitudinal stability of 1.7% (coefficient of variation, CV). Additional scans were performed with the phantom rotated by up to 20° in each of the three orthogonal planes to assess the effects of variable patient positioning. Horizontal and vertical rotation of the spine had little effect on the estimated bone mineral density (BMD), however, axial rotation of greater than 8° led to errors in the BMD measurement. One hundred consecutive patients had two lateral scans performed within 1 month. BMD (range 0.10–1.6 g/cm²) was determined for each scan by one operator. Significant overlap from ribs and pelvis was often seen with L2 and L4 vertebrae but one vertebra (L3) could be measured in every case. Intraoperator and interoperator variability was assessed by three experienced operators, each analyzing 10 patients' scans on five separate occasions, and was found to be less than 1.1% for a single vertebra. BMD estimation of vertebral bodies and midslices by lateral DEXA scans (CV% of 3.8% and 4.6%) have a 95% confidence interval of 0.074 g/cm² and 0.096 g/cm², respectively for two vertebrae. This variability is due mainly to axial rotation, with operator variability, horizontal rotation, and vertical rotation having little effect on BMD estimation.     

The accuracy of volumetric bone density measurements in dual X-ray absorptiometry

New developments in dual x-ray absorptiometry (DXA) allow the performance of high precision anteroposterior (AP) and lateral scans of spinal bone mineral density (BMD, units: g/cm²) without the patient moving from the supine position. Data from both projections may be combined to give an estimate of the true volumetric bone mineral density (VBMD, units: g/cm³) of the lumbar vertebral bodies. This report presents a cadaver study designed to validate DXA measurements of volumetric bone density. Sections of whole lumbar spine were scanned in AP and lateral projections in a water tank to simulate soft tissue. Individual vertebrae were then divided to separate the vertebral body from the neural arch, and vertebral body volume was measured using the displacement of sand. The bone mineral content (BMC) of vertebral bodies and neural arches was measured by ashing at 250°C for 60 hours followed by 500°C for a further 24 hours. The results showed that DXA scanning systematically underestimated ashing data by 14% for AP BMC, 33% for vertebral body BMC, 23% for vertebral body volume, and 12% for VBMD. Despite these significant systematic errors, the DXA measurements and ashing values were highly correlated (r=0.979-0.992). The results suggested that after allowing for the systematic errors, lateral DXA parameters related closely to true BMC, volume, and VBMD.     

Patient variables impact lumbar spine dual energy X-ray absorptiometry precision

Introduction Changes in bone mineral density are used to monitor osteoporosis therapy. To determine whether a change in bone mass is clinically significant, the precision of bone mineral density measurements must be known. Methods We therefore measured the impact of vertebral body exclusion on dual energy X-ray absorptiometry (DXA) precision. At one university and one Veterans Affairs DXA center, three radiology technologists each scanned 30 participants twice, with repositioning between scans, to estimate DXA precision. Three International Society for Clinical Densitometry-certified physicians reviewed all lumbar spinal scans to note the presence of focal structural defects. We calculated precision for subsets of vertebrae, and for virtual samples of patients with and without physician-identified vertebral focal structural defects. We graphed the reciprocal of least significant change versus bone area to determine the dependence of precision on interpreted scan area. Results Within each sample, greater interpretable bone area improved precision. The contribution of interpreted bone area to precision differed among the samples, ranging from 57 to 94%. Greater population bone mineral density heterogeneity and presence of focal structural defects each decreased precision. Conclusion All bone densitometry centers must determine precision using a sample representative of their served populations. Failure to do so may lead to incorrect determination of least significant change. Population heterogeneity, vertebral body exclusion and presence of focal structural defects each decreases precision.     

Measurement of periprosthetic bone mineral density after cementless hip arthroplasty by dual energy X-ray absorptiometry: Longitudinal and cross-sectional evaluation

To clarify changes in bone mass around a femoral prosthesis, periprosthetic bone mineral density (BMD) was measured by dual energy X-ray absorptiometry (DXA) in 60 patients after unilateral cementless hip arthroplasty. Changes in BMD were evaluated by cross-sectional analysis in all patients and by longitudinal analysis in 26 patients who were available for measurement from 1 month to 2 years after surgery. The mean reproducibility of BMD measurements was within 1.74% in vivo. Periprosthetic BMD began to decrease early after surgery, and although it recovered temporarily within 1 year, it did not return to the level of the 1st month even after 2 years. BMD was reduced by 30.4% in the whole periprosthetic region compared with the contralateral untreated femora 4–7 years after surgery. The reduction in BMD was remarkable around the proximal part of the stem, especially in zone 7 (44.7% reduction 4–7 years after surgery). Significant positive correlations were observed between the low level of the preoperative cortical remodelling index and the reduction in BMD and between the preoperative femoral BMD and the reduction in BMD, indicating that the postoperative bone loss was greater in patients who preoperatively showed quantitative and qualitative deterioration of the femur. Abstracts of this paper were presented at the 66th and 67th Annual Meeting of the Japanese Orthopaedic Association, the 19th Conference of Société Internationale de Chirurgie Orthopédique et de Traumatologie (SICOT), and the 20th Conference of the Japanese Hip Society     

双能X线和单光子吸收法及定量超声诊断骨质疏松症的比较

了解三种方法诊断骨质疏松症（ＯＰ）之间的关系。方法应用双能Ｘ线吸收法（ＤＸＡ）和单光子吸收法（ＳＰＡ）及定量超声（ＱＵＳ），同时随机测量２９４例受试者腰椎后前位和侧位、左侧髓部和前臂骨矿密度（ＢＭＤ）及右侧胫骨超声速度（ＳＯＳ）。结果ＤＸＡ和ＳＰＡ测量桡骨ＯＰ的检出率分别为２５．９％和２１．４％，ＤＸＡ测量腰椎后前位、侧位、侧位兴趣区、Ｗａｒｄ’ｓ区和股骨颈ＯＰ检出率分别为１６．０％、２２．８％、２６．２％、１９．４％和４．４２％，ＱＵＳ的ＯＰ检出率为１７．７％。三种方法及不同部位之间的测量结果呈显著相关（ｒ＝０．４９４～０．９６７，Ｐ＜０．０１）。ＤＸＡ测量前臂１／３处ＢＭＤ显著高于ＳＰＡ。诊断ＯＰ的齐同率ＤＸＡ各部位相互之间平均为４０．１％±１５．５％，ＤＸＡ与ＳＰＡ平均为４８．４％±１９．０％，ＱＵＳ与ＤＸＡ和ＳＰＡ平均为３８．８％±１０．２％，各平均值之间无显著差异。结论ＯＰ的检出率取决于受检部位，腰椎侧位兴趣区和挠骨是检出率最高的部位，股骨颈和尺骨是最低的部位。ＳＰＡ与ＤＸＡ测量前臂ＢＭＤ高度相关，诊断结果无显著性差别。     

First all-solid pediatric phantom for dual X-ray absorptiometry measurements in infants.

Manufacturer-supplied lumbar spine phantoms are normally used for quality control of dual X-ray absorptiometry (DXA) instruments. Presently, there is no pediatric phantom for whole-body mineralization and softtissue composition DXA measurements. We designed blocks of acrylic (for fat mass), polyvinyl chloride (for lean mass), and aluminum (for bone mass) whose combination provides five whole-body phantoms ("Inphants") that mimic body weight and composition during the first year of life and help solve problems that require repeated scans in stable conditions. Inphants were scanned using an Hologic QDR 2000. Comparisons were made between values obtained with and without the table pad, using infant software. Then we compared data obtained using infant and adult softwares successively in the same phantoms. The table pad significantly influenced DXA measurements. We observed significant differences in fat mass (p = 0.04) and lean mass (p = 0.03) with the smaller Inphant (3 kg) and in bone mineral content (BMC) (p = 0.02) with the larger Inphant (13 kg). BMC was three to five times lower with adult than with infant software. Adult software yielded systematically significantly lower fat masses but higher lean masses than infant software. Because there was no overlap with larger Inphants, we calculated conversion formulae between values of infant and adult software. The results suggest guidelines for scan acquisition and analysis in young subjects.     

单能与双能X线吸收法测量骨密度的比较

应用单能Ｘ线测量（ＳＸＡ）及双能Ｘ线测量（ＤＥＸＡ）法测量北京地区正常妇女骨密度，对两种方法进行比较，以选择反映骨丢失敏感的部位。共测量３００名，年龄为２０～７９岁，每岁５名，测量部位分别为ＳＸＡ法的非优势前臂远端（８ｍｍ－Ｄ）、１／４远端（１／４－Ｄ）、超远端（Ｕｌｔｒａ－Ｄ），ＤＥＸＡ法的腰椎正位（Ｌ２－４）、右股骨颈（Ｎｅｃｋ）、Ｗａｒｄ＇ｓ三角（Ｗａｒｄ）及粗隆区（Ｔｒｏｃｈ），两种方法各有１０名妇女进行了仪器重复性检验。Ｎｅｃｋ、Ｗａｒｄ骨密度峰值分布在２０～２９岁，Ｕｌｔｒａ－Ｄ、Ｌ２－４ＢＭＤ分布在３０～３９岁，８ｍｍ－Ｄ、１／４－Ｄ、Ｔｒｏｃｈ分布于４０～４９岁年龄组。所有部位ＢＭＤ在峰值后随年龄增长逐渐降低，８ｍｍ－Ｄ年下降率最高（１．１６％）。两种方法测得７个部位ＢＭＤ值之间均有显著相关。与绝经前相比，绝经后妇女各部位ＢＭＤ值下降迅速，尤以绝经后１１～１５年内显著，其中Ｗａｒｄ三角下降率最高为４２．９％。     

DXA在体成分测定方面的应用进展

在代谢综合征等疾病状态下,体成分测定比体重更有意义。体成分包括体内脂肪组织和瘦组织分布及百分组成,其测定方法有二分法和三分法等。双能X线骨密度测定(DXA)属于三分法,精确度高完全可以替代CT测量腹部和内脏脂肪。     

DXA在诊断主动脉钙化中的应用进展

双能X线骨密度吸收仪(DXA)通常被用于测定骨密度(BMD)以诊断骨质疏松,近年研究发现,DXA同时应仔细观察主动脉有无钙化,而主动脉钙化是冠心病的重要危险因素,发现异常者应结合被检者的年龄、冠心病风险因素等情况提出进一步检查的建议。这样,在检测骨密度的同时检测主动脉的钙化,无论是对骨质疏松还是冠心病的发生均可以起到早期诊断、早期治疗的目的 。     

Regional bone mass measurement from whole-body dual energy X-ray absorptiometry scan.

There are no data on the relative accuracy and precision of regional bone mass measurement from whole-body dual energy X-ray absorptiometry (DXA) scans in small young subjects. Twelve domestic swine piglets (2550-17,660 g) were scanned on a single-beam and on a fan beam densitometer using each humerus and femur as the region of interest to determine the validity of five different scan modes: two infant whole body (IWB), two spine, and one rat whole body (RWB) scan mode in the determination of regional bone mass measurements. DXA bone mineral content (BMC( measurements from RWB and IWB fan beam and IWB single-beam scans were highly predictive of ash weight (adjusted r2 = 0.98, 0.94, 0.94, respectively). Correlation between left and right limbs was highly significant (p < 0.001 for all comparisons) for ash weight (r = 0.99) and for DXA measurements of BMC (r = 0.92-0.99), area (r = 0.92-0.99), and bone mineral density (r = 0.87-0.99) for all modes of DXA scan. Repeatability (as standard deviation of differences of repeated scans) varied with scan mode and DXA parameters and ranged from 1.5 to 7.6%and from 1.8 to 14.7% for intra-and interoperator, respectively. We conclude that regional DXA measurements from IWB and RWB scans can be assessed accurately and with adequate precision for clinical use in subjects with low bone mass comparable with infants and young children. The RWB scan is useful for research studies. However, appropriate training and documentation of precision errors is needed to minimize repeatability errors.     

DXA诊断椎体压缩性骨折的应用进展

椎体压缩性骨折不仅是骨质疏松的主要临床表现之一,而且在预测骨折风险中具有重要意义,双能X线骨密度吸收仪(DXA)从最初的一种定量测量仪器发展到可以进行成像,目前已经可以用椎体侧位DXA成像来诊断椎体骨折并进行椎体骨折评估,可以更好的了解骨骼状态,而且放射暴露比普通X片低得多,本文就DXA在椎体压缩性骨折诊断方面的进展综述如下.