Broadband ultrasound attenuation and dual energy X-ray absorptiometry in patients with hip fractures: Which technique discriminates fracture risk

There is considerable interest in predicting risk of hip fracture in order to allow targeting of preventive care. This study aimed to determine which of two methods best discriminates a hip fracture population from controls. Fifty women with fractured neck of femur, and 50 control subjects were scanned using dual energy X-ray absorptiometry (DXA) of the spine and hip and broadband ultrasound attenuation (BUA) of the os calcis. Significant differences between the two populations could be found for both DXA and BUA, with BUA showing the largest percentage difference (27%). The mean z-scores showed that BUA had the lowest, with the exception of DXA trochanter. However, no significant difference between BUA and DXA trochanter Z-scores was found. A receiver operator characteristic (ROC) analysis showed that BUA has a superior sensitivity and specificity compared with DXA measurements, with DXA of the hip being better than the spine. This retrospective study shows that BUA is a better discriminator of hip fracture than DXA lumbar spine of DXA hip, which may have important implications for predicting those at risk of future hip fracture.     

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.     

Ultrasound attenuation of the Os calcis in women with osteoporosis and hip fractures

Summary Bone ultrasound attenuation of the calcaneus, and vertebral and femoral bone density measured by dual photon absorption were determined in 22 women with osteoporosis, 10 women with hip fractures, and 29 normal, age-matched controls to determine the utility of the ultrasound technique as an indicator of axial osteopenia. Vertebral and femoral neck density and bone ultrasound attenuation were significantly decreased (P<0.01) in the women with osteoporosis and those with hip fractures. The sensitivity and specificity of bone ultrasound attenuation was 80% at a value of 50 dB/MHz. At 90% specificity the sensitivity of bone ultrasound attenuation was 65%. The results of this pilot study suggest that ultrasound attenuation, a safe, simple, and radiation-free procedure, may be utilized as an indicator of decreased axial bone mass.     

DXA 髋结构分析参数预测髋部脆性骨折的价值

目的探讨双能X线吸收测量法(DXA)髋几何力学参数在预测髋部脆性骨折风险中的应用价值。方法髋部骨折女性患者41例(年龄52.3~89.4岁)及正常对照组259例(年龄28.2~88.3岁)行DXA扫描获取股骨颈骨密度(femur neck BMD,FN_BMD)及髋几何力学分析参数,包括股骨颈横截面惯性矩(CSMI)、股骨颈横截面面积(CSA)、截面模数(SM)、曲率比率(BR)、颈宽度(FNW)、髋轴长(HAL)、股骨颈干角(NSA),并计算股骨近端强度指数(FSI)。利用受试者工作特征曲线(ROC)分析相关变量判定髋部骨折的效能。结果校正年龄、身高、体重、BMI混杂因素,髋部骨折组与非骨折组间FN_BMD差异有显著性意义(P0.01),髋部骨折组FSI、SM、CSMI、CSA较非骨折组低(P均0.05),而BR、FNW、NSA、HAL较非骨折组高(P均0.05);当校正FN_BMD时,只有FSI、NSA及HAL在两组间差异仍有统计学意义(P均0.05)。控制混杂因素,FN_BMD与FSI(r=0.339)、BR(r=-0.291)、SM(r=0.644)、CSMI(r=0.425)、NSA(r=-0.291)呈轻-中度相关性,FN_BMD与CSA相关密切性最好(r=0.908,P0.001)。FN_BMD、FSI、HAL、NSA判定髋部骨折的ROC曲线下面积(AUC)分别为0.794±0.031、0.790±0.032、0.652±0.049、0.684±0.049。FN_BMD及FSI判定髋部骨折的效能相仿(P=0.9128)。FN_BMD联合FSI判定髋部骨折的AUC为0.844±0.039,较FN_BMD大(P0.05)。结论 FSI独立于FN_BMD起作用,可作为判断骨质疏松性髋部骨折的有用因子。FN_BMD联合FSI可以提高预测髋部骨折风险的能力。     

Bone mineral density in chinese elderly women with hip fracture

In order to examine the status of osteoporosis of the patients with hip fracture, we assessed the bone mineral density (BMD) of the contralateral hip of 81 elderly females with hip fracture and compared those with 77 normal Chinese women. The age of fracture subjects was 73.5±6.6 years (mean±SD), and 69.2±6.9 years for the controls. All of these fractures were caused by minor trauma, such as falls from a standing position or slipping to the ground. The Norland 2600 dual-photon absorptiometer (DPA) was used to evaluated the BMD in the femoral neck, trochanter, and Ward's triangle areas. The BMD for the fracture subjects was significantly lower than those of the controls. By linear regression, the probability of fracture increased exponentially with age and low BMD. The mean BMD for femoral neck of the fracture subjects versus controls was 0.556 versus 0.624 g/cm²; for trochanter: 0.505 versus 0.566 g/cm²; for Ward's triangle: 0.432 versus 0.485 g/cm². Both negative predictive value (NPV) and positive predictive value (PPV) were acceptable at the prevalence of hip fracture of 5% or 20% and at a cutoff point of 0.65 g/cm². These data revealed that the degree of relative osteoporosis in the patients with hip fractures was more severe than that of controls.     

Ultrasound bone densitometry of Os calcis in elderly Japanese women with hip fracture

We evaluated 138 elderly patients (mean age 79 years) within 2 weeks after hip fracture (67 cervical and 71 trochanteric) using an Achilles ultrasound bone densitometer (Lunar Corporation, Madison, WI). The ultrasound variables of speed of sound (SOS in m/second), broadband ultrasound attenuation (BUA in dB/MHz), and stiffness (%) index were measured on the os calcis. Ultrasound densitometry also was done on 563 normal postmenopausal women to assess normal age changes. An elderly subgroup (n = 138) served as age-matched controls for the hip fracture group. Further subgroups of 33 patients and 33 controls were compared for lumbar spine and femoral neck BMD. There were no statistically significant differences between the hip fracture group and age-matched controls in height and weight, but each ultrasound variable was significantly lower for the hip fracture group (P < 0.0001). For the hip fracture group, SOS was 1470 ± 19 m/second, BUA was 84.3 ± 8.4 dB/MHz, and the stiffness index was 47.8 ± 9.2%, whereas for the age-matched controls, SOS was 1486 ± 27 m/second, BUA was 94.0 ± 11.4 dB/MHz, and the stiffness index was 59.1 ± 12.5%. There were no significant differences between cervical and trochanteric hip fracture groups. Logistic regression analysis showed that a change of the ultrasound values by 1 standard deviation (SD) changed the odds ratio for SOS, BUA, and stiffness index by 2.51, 3.24, and 3.60, respectively. Ultrasound variables, particularly stiffness, were good indicators of hip fracture risk. Received: 7 June 1995 / Accepted: 14 June 1996     

Ultrasound and dual X-ray absorptiometry measurement of the calcaneus: Influence of region of interest location

Ultrasound measurements of the calcaneus are related to incidence of osteoporotic fracture. Such measurements are generally made at fixed coordinates relative to a footplate. This study compares measurements at an anatomically located region of interest (ROI_anat) and at fixed coordinates (ROI_fixed), with bone mineral density measurements, in 84 postmenopausal women. Bone mineral density (BMD) was assessed using dual energy X-ray absorptiometry at both ROIs as well as at lumbar spine and femoral neck. Broadband ultrasound attenuation and velocity of sound were measured using a CUBA system at ROI_anat and ROI_fixed. Additionally, broadband ultrasound attenuation at ROI_fixed was measured using a Walker Sonix instrument. Mean bone mineral density, broadband ultrasound attenuation and velocity of sound did not differ significantly between ROI_fixed and ROI_anat, although broadband ultrasound attenuation by Walker Sonix (81.4±14.6 dBMHz^-1) was significantly (P<0.001) greater than that by CUBA (63.7±14.2 dBMHz^-1). The relationship between broadband ultrasound attenuation and BMD differed significantly between the 2 ROIs and the correlation of this relationship was significantly greater at ROI_fixed than at ROI_anat (r=0.74 versus 0.46, P<0.01). The differing relationship may reflect structural variation at different regions. ROI selection may thus be a possible confounding factor in ultrasound measurement.     

Broadband ultrasound attentuation compared with dual-energy X-ray absorptiometry in screening for postmenopausal low bone density

Broadband ultrasound attenuation (BUA) was investigated as an inexpensive, simple and radiation-free method of screening for low perimenopausal bone density. A total of 587 women (50–54 years), invited for screening had bone mineral density (BMD) measured at the femoral neck and the lumbar spine by dual-energy X-ray absorptiometry (DXA). At the same visit the BUA of the calcaneus was measured. The correlation between BUA and BMD was approximately 0.4 compared with 0.67 between femoral neck and spinal BMD. Receiver operating characteristic (ROC) curve analysis demonstrated BUA to have the same ability for discriminating between low BMD at either the femoral neck or lumbar spine. BUA with a cut-off for normality at the median (BUA=80) had a sensitivity of 68% and specificity of 67% for low bone density identified by a BMD less than the 25th centile at the femoral neck or lumbar spine. The correlation between BUA and BMD was insufficient to allow identification of the same groups as having low bone density.     

跟骨超声骨质测量与双能量X线吸收骨密度测量的比较

我们试图通过对跟骨超声骨质测量仪与双能量Ｘ线吸收骨密度测量仪的临床对比，来评价跟骨超声骨质测量仪的敏感性。本文对５６名健康女性同时接受了超声骨质测量仪和双能量Ｘ线吸收骨密度仪的检测。３７例（年龄２６～７６岁）进行了跟骨超声和腰椎骨密度测量，１９例（年龄２６～７０岁）进行了跟骨超声和股骨颈骨密度测量。结果用ＳＹＳＴＡＴ统计软件包进行处理。结果表明：随着年龄的增加，腰椎、股骨颈骨密度及跟骨强度（Ｓｔｉｆｆｎｅｓｓ）均显著下降（Ｐ＜０．０５），两种仪器的阳性检出率无明显差异（Ｐ＜０．０５）。但腰椎和股骨颈ＢＭＤ与跟骨强度（Ｓｔｉｆｆｎｅｓｓ）的相关性适中ｒ＝０．４６５～０．５１３左右。通过逐步多元回归分析显示超声强度（Ｓｔｉｆｆｎｅｓｓ）与ＢＭＤ无关。这表明超声波测量仪主要测量骨的结构变化，而骨密度测量仪则是测量骨量的变化。两种方法相辅相承，共同测量，将更好地预测骨质疏松性骨折的发生。同时超声波具有无放射线损害、价格低廉及良好的敏感性，将越来越受到临床重视。     

骨质疏松与老年髋部骨折

目的观察60岁以上的老年人与同性别年轻人骨密度峰值的差别,老年髋部骨折患者与同年龄组健康老年人骨密度的差异,及近11年来老年髋部骨折发生的一般规律。探索老年髋部骨折与骨质疏松的关系。方法测量20~35岁年龄组正常男性和女性的腰椎、股骨颈、Ward三角及大转子区的骨密度值;测量60岁以上健康老年男性及女性各年龄组的骨密度值;测量60岁以上新入院髋部骨折男、女性患者的骨密度值。所有结果均进行统计学处理。统计近11年来收治的445例60岁以上髋部骨折患者的年龄、性别分布规律。结果60岁以上的男、女性老年人与同性别年轻人骨密度比较,差异有显著性意义(P<0.01);健康老年男性骨密度明显高于同年龄组女性(P<0.01);健康老年男、女性骨密度明显高于同年龄组髋部骨折患者(P<0.01);对近11年来收治的445例老年髋部骨折患者的性别、年龄进行比较,差异无显著性意义。结论虽然老年骨折常由外伤引起,但骨质疏松是老年人骨折的重要内在因素;尽管老年男性比女性骨密度高,但两者的骨折机会及骨折发生率基本相同。     

Fundamentals and pitfalls of bone densitometry using dual-energy X-ray absorptiometry (DXA)

Measurement of bone mineral density (BMD) with central dual-energy X-ray absorptiometry (DXA) is the current gold standard for diagnosing osteoporosis and for monitoring patients. Errors in demographic information, improper patient positioning, incorrect scan analysis, and mistakes in interpretation can all lead to a wrong clinical decision or action. This paper reviews the fundamentals of positioning, scan analysis, and interpretation for central DXA and highlights some of the common pitfalls that may lead to erroneous results.     

Dual-energy X-ray absorptiometry of the calcaneus: Comparison with vertebral dual-energy X-ray absorptiometry and quantitative computed tomography

The purpose of this study was to determine the efficacy of using bone mineral measurements of the calcaneus to evaluate osteoporosis. Dual energy X-ray absorptiometry (DXA) of the calcaneus was compared with posteroanterior lumbar absorptiometry (DXA) and vertebral quantitative computed tomography (QCT) measurements in 171 white women (78 normal and 93 osteoporotic). DXA measurement of os calcis mineralization decreased significantly in osteoporosis, but to a lesser extent than in vertebral sites. In normal subjects, good correlations were observed between calcaneal and lumbar DXA (0.69) and QCT (0.56). In subjects with vertebral fractures, there was also good correlation between calcaneal DXA and QCT (0.59–0.69). This suggests that trabecular bone in calcaneus and vertebrae have related involution in cases of vertebral osteoporosis. However, the extent of bone loss is less marked in the calcaneus than in the vertebrae and is not sufficient to be accurately measured over time. We conclude, therefore, that although the global densitometric measurement at this site is not sufficiently sensitive for general use, it can be useful as a epidemiological research tool.     

骨密度结合股骨近端几何参数预测老年髋部骨折

目的研究老年人骨密度(Bone mineral density,BMD)值结合股骨近端几何参数是否能提高骨质疏松性髋部骨折危险性的预测。方法将85例绝经后妇女髋部骨折患者按骨折类型分组, 其中52例股骨颈骨折,33例转子间骨折。对照组100例老年女性。在骨盆片上测量股骨近端几何参数,在股骨颈、Ward’s三角和转子处测量BMD值,对结果进行统计学处理分析。结果骨折组的BMD值均低于对照组(P<0．01);股骨干皮质厚度与股骨颈BMD值有相关性(r=0．45,P< 0．01);逐步线性回归分析结果显示股骨距内侧皮质厚度、转子处BMD值、颈干角和Ward’s三角 BMD值相结合是预测髋部骨折最好方法(r=0．74,r2=0．53,P<0．01)。结论骨密度值结合放射学测量股骨近端几何参数能提高对骨质疏松性髋部骨折及骨折类型的预测。     

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.     

Low serum concentrations of Irisin are associated with increased risk of hip fracture in Chinese older women

Objective

Irisin derived from muscle in response to exercise may be the molecular entity responsible for muscle wasting-osteoporosis connectivity in the elderly. The objective of the study was to determine whether serum Irisin (sIrisin) provides information on hip fracture prediction which were independent of bone mineral density (BMD) and the fracture risk assessment tool (FRAX) algorithm.

Ultrasound attenuation of the calcaneus: A sensitive and specific discriminator of osteopenia in postmenopausal women

Summary Recent studies have evaluated techniques for estimating bone mass without radiation. The present study compares broadband ultrasound attenuation of the calcaneus and bone densities of the femoral neck and the lumbar spine in 17 normal women and 41 women with osteoporosis. Twenty of the osteoporotic women had spine (n=16) or femoral neck (n=4) fractures. There was a significant decrease in the broadband ultrasound attenuation (P<0.001) in women with osteoporosis compared with normal women. The osteoporotic women also showed a decrease in vertebral (P<0.0001) and femoral neck (P<0.0001) densities compared with normal women. At 63 dB/MHz, the sensitivity and specificity of broadband ultrasound attenuation for decreased bone mineral density with or without fractures were 76%. All women with fractures had a broadband ultrasound attenuation less than 72 dB/MHz. This corresponded to a specificity of 41%. To determine whether broadband ultrasound attenuation correlated with trabecular bone volume, samples of cadaver calcaneus were analyzed. The histologic determination showed a significant correlation between broadband ultrasound attenuation and trabecular bone volume (r=0.992,P=0.008). These results suggest broadband ultrasound attenuation of the calcaneus reflects bone mass and can be used as a safe and sensitive indicator for decreased axial bone density.     

Bone densitometry of the forearm: Comparison of single-photon and dual-energy X-ray absorptiometry

Forearm bone mineral densitometry was performed initially by single-photon absorptiometry (SPA), but is now achievable by dual-energy X-ray absorptiometry (DXA) as well, with a good correlation between both measurements. However, it is still unknown whether: (1) short-term precision of DXA is superior to SPA and (2) identical regions of interest (ROT) are mandatory to correlate SPA with DXA. The aim of this study was to answer these questions using a commercial system for DXA (DXA-FAS) and to test an in-house system using spine DXA and a soft-tissue compensator (DXA-STC). In ten subjects, four measurements on the same day showed significantly lower (p < 0.05) coefficients of variation (CV) for bone mineral density (BMD) by DXA-FAS (proximal site: 0.74%; ultradistal site: 1.20%) than by SPA (1.26% and 2.25%). However, the CV for bone mineral content (BMC) were similar for DXA-FAS (0.73% and 1.58%) and SPA (0.79% and 1.34%). The significant difference (p < 0.05) for surface calculation by DXA-FAS (1.24% and 0.93%) compared with SPA (2.36% and 1.28%) explains all the advantages of DXA-FAS for short-term precision. The measurements taken on the same day on the ulna and the radius or on the radius alone by SPA, DXA-FAS, and DXA-STC on 108 subjects aged 18–80 years were highly correlated [r ranging from 0.925 to 0.995 (p < 0.0001) and standard error of the estimate from 3.15% to 8.89%]. The need for a manual adjustment of the ROT was found to be mandatory for BMC but not BMD assessment. The use of DXA-STC is a fast method for forearm bone densitometry and its correlation with SPA is very high. However, its short-term precision for BMC (3.00% and 1.54%), BMD (2.15% and 1.12%), and surfaces (1.99% and 1.12%) is significantly higher (p < 0.05) than that of DXA-FAS. We conclude that short-term precision of DXA is better than that of SPA only for BMD and surface measurement but not for BMC. ROT should be adjusted manually for the assessment of BMC but not for that of BMD.     

Ultrasound and densitometry of the calcaneus correlate with the failure loads of cadaveric femurs

We assessed the bone mineral density (BMD) of 16 matched sets of cadaveric proximal femurs and feet using dual-energy x-ray absorptiometry (DXA). We also estimated the femoral neck length from the DXA scans. Quantitative ultrasound densitometry was used to measure the velocity of sound and broadband ultrasound attenuation (BUA) in the calcaneus of each foot. The proximal femurs were then tested to failure in a loading configuration designed to simulate a fall with impact to the greater trochanter. Femoral neck BMD and trochanteric BMD were strongly associated with the femoral failure load (r²=0.79 and 0.81, respectively; P<0.001), whereas femoral neck length was modestly correlated with femoral failure load (r²=0.27, P=0.04). Calcaneal BMD (r²=0.63, P<0.001) and BUA (r²=0.51, P=0.002) were also significantly associated with femoral failure load. Given the small sample size, we were unable to detect differences in the strength of the correlations between the independent parameters and femoral failure load. Using linear multiple regression analyses, the strongest predictor of femoral failure load was a combination of femoral neck BMD and femoral neck length (R²=0.85, P<0.001). Thus, it appears that both femoral and calcaneal bone mineral properties may be useful for identifying those persons at greatest risk for hip fracture.     

The association of patellar ultrasound transmissions and forearm densitometry with vertebral fracture,number and severity: The saunders county bone quality study

Ultrasonic measures of bone have been available for clinical research purposes for nearly 10 years, yet there still seems to be a need to compare ultrasound with the accepted gold standard of densitometry. Recently there have been published reports showing that ultrasound measures are associated with both appendicular and hip fracture, in particular after adjustment for densitometry measures. We present here a comparison between speed of sound through the patella and forearm bone densitometry, using their association with prevalent vertebral fractures in a population-based study of women and men. The prospective phase of the Saunders Bone Quality Study includes 1401 women and men who had baseline spine radiographs, patellar ultrasound, and forearm densitometry measurements. Multivariate forward logistic regression was used to determine the age-adjusted odds of vertebral fracture, the number of fractures, and the severity of these fractures, when patellar ultrasound and each of four forearm densitometry measures were entered into the model. Age is the most important factor associated with vertebral fractures, their number, and severity for women, while age is not significantly related to vertebral fractures for men. Of the bone status measures, patellar ultrasound entered the logistic regression models more consistently than any other measure except ulnar bone mineral density for women. The ultrasound measure entered every model for men. We conclude that patellar ultrasound velocity is more consistently associated with the odds of vertebral fractures than radius bone mineral content.     

A comparison of spinal quantitative computed tomography with dual energy X-ray absorptiometry in European women with vertebral and nonvertebral fractures

Quantitative computed tomography (QCT) was compared to dual X-ray absorptiometry (DXA) measured in the lumbar spine of 508 European women defined as normal without fracture (NoF), or osteoporotic (OP), with either vertebral fracture (VF), or peripheral fracture (PF). The correlations between QCT and DXA BMD measurements were significantly different in normal and in osteoporotic patients, indicating that the two exams do not measure the same bone aspects. According to ROC curves results, QCT Z-scores separate OP from NoF with better sensitivity than all other measurements. A threshold to differentiate OP from NoF was chosen at Z-score=−1 for DXA-BMD and −1.5 for QCT-BMD. VF patients showed a highly significant decrease in BMD by DXA or QCT. PF patients revealed measurements lower than those of normal subjects but greater than those of VF, calling into question the idea of a diffuse osteoporosis causing nonvertebral fractures that is measurable by spinal DXA or QCT. DXA is weakly dependent upon age, and T-score or Z-score are equivalent for evaluating osteoporosis. QCT depends greatly upon age, and Z-score appears to be more efficient.