Which bone densitometry and which skeletal site are clinically useful for monitoring bone mass?

Long-term precision, as well as reproducibility, is important for monitoring bone mineral density (BMD) alteration in response to aging or therapy. In order to investigate which bone densitometry and which skeletal site are clinically useful for monitoring bone mass, we examined the standardized long-term precision of several bone density measurements in 83 healthy Japanese women. Annual BMD measurements were performed for 5 or 6 years using dual X-ray absorptiometry (DXA) on the lumbar spine, radius (EXP5000) and calcaneus (HeelScan); peripheral quantitative computed tomography (pQCT) on the radius (Densiscan1000); and quantitative ultrasound (QUS) on the calcaneus (Achilles+). The long-term precision error for the individual subject was given by the standard error of estimate (SEE), and the standardized long-term precision was defined as the percentage coefficient of variation (CV%) divided by the percentage ratio of the annual bone-loss rate. Based on the CV% of spinal DXA, speed of sound (SOS) and diaphyseal pQCT showed significantly higher precision than others, while radial ultradistal (UD) DXA and heel DXA showed significantly lower precision. The long-term precision errors of other measurements were statistically the same as that of the spinal DXA. The spinal DXA, the radial DXA, and pQCT at both the distal metaphysis and diaphysis showed high rates of annual bone loss. The radial trabecular BMD (pQCT) was significantly higher than that of spinal DXA. The annual rates of bone loss of QUS and of heel DXA were significantly lower than that of spinal DXA. Taken together, standardized long-term precision was obtained in the spinal DXA and radial pQCT. In conclusion, spinal DXA and radial pQCT were considered the most useful monitoring method for osteoporosis, while QUS was considered less useful.     

Estimation of distal radius failure load with micro-finite element analysis models based on three-dimensional peripheral quantitative computed tomography images

There is increasing evidence that, in addition to bone mass, bone microarchitecture and its mechanical load distribution are important factors for the determination of bone strength. Recently, it has been shown that new high-resolution imaging techniques in combination with new modeling algorithms based on the finite element (FE) method can account for these additional factors. Such models thus could provide more relevant information for the estimation of bone failure load. The purpose of the present study was to determine whether results of whole-bone micro-FE (μFE) analyses with models based on three-dimensional peripheral quantitative computer tomography (3D-pQCT) images (isotropic voxel resolution of 165 μm) could predict the failure load of the human radius more accurately than results with dual-energy X-ray absorptiometry (DXA) or bone morphology measurements. For this purpose, μFE models were created using 54 embalmed cadaver arms. It was assumed that bone failure would be initiated if a certain percentage of the bone tissue (varied from 1% to 7%) would be strained beyond the tissue yield strain. The external force that produced this tissue strain was calculated from the FE analyses. These predictions were correlated with results of real compression testing on the same cadaver arms. The results of these compression tests were also correlated with results of DXA and structural measurements of these arms. The compression tests produced Colles-type fractures in the distal 4 cm of the radius. The predicted failure loads calculated from the FE analysis agreed well with those measured in the experiments (R² = 0.75 p < 0.001). Lower correlations were found with bone mass (R² = 0.48, p < 0.001) and bone structural parameters (R² = 0.57 p < 0.001). We conclude that application of the techniques investigated here can lead to a better prediction of the bone failure load for bone in vivo than is possible from DXA measurements, structural parameters, or a combination thereof.     

Comparison of pQCT-Based Measures of Radial Bone Geometry and Apparent Trabecular Bone Structure Using Manufacturer and In-House-Developed Algorithms

Peripheral quantitative computed tomography (pQCT) provides noninvasive densitometric and morphometric measures of total, trabecular, and cortical bone compartments. Skeletal changes over time can be determined by repeated measurements. Image thickness of 2.5 mm is thought to be advantageous with respect to test-retest reliability through interrogation of a significant tissue volume. However, the error associated with slight shifts in image location is unknown. The primary purpose of this study was to determine the effects of positional variability around the 4% site on radial bone measures. The secondary objective was to compare different software algorithms for estimating the same bone characteristics. Eight left cadaveric forearms (aged 65–88 yr) were imaged at 0.5-mm intervals around the 4% site of the radial bone using pQCT (10 slices; in-plane resolution: 0.2 × 0.2 mm; thickness: 2.5 mm; Stratec XCT2000L. We used the manufacturer’s software (Stratec v6.0B) to determine the total bone mineral density (BD_tot), total bone mineral content (BMC_tot), total bone area (Area_tot), trabecular bone mineral density (BD_trab), trabecular bone mineral content (BMC_trab), and trabecular bone area (Area_trab) from each image. For comparison, in-house-developed software was also used to analyze Area_tot and Area_trab at the 4% site. The in-house software also produced measures of apparent trabecular structure, including number (App.Tb.N), thickness (App.Tb.Th), and spacing (App.Tb.Sp), quantified using 2 different stereological approaches: the parallel-plate method using trabecular perimeter lengths and mean intercept length analysis. The effect of slice position was assessed using a 1-way repeated-measures analysis of variance (ANOVA). Reliability of nonsignificant slice distances around the 4% site was determined using intraclass correlation coefficients (ICCs). One-way repeated-measures ANOVA was used to compare measures of similar bone characteristics at the 4% site. Bland-Altman plots were created to assess the level of agreement between pairs of algorithms quantifying comparable apparent trabecular structure. Area_tot and Area_trab differed significantly at greater than or equal to 1.0 mm proximal and greater than or equal to 0.5 mm distal to the 4% site. BMC_tot and BMC_trab differ significantly greater than or equal to 1.5 mm proximally (for both) and greater than or equal to 2.0 and 1.0 mm distally, respectively. BD_tot differed significantly at greater than or equal to 1 mm proximal and distal to the 4% site. BD_trab did not differ among the 10 slices. For images acquired at the 4% site, and 0.5 mm more proximally, reliability was excellent (ICC = 0.98 to 0.99). Although the in-house software yielded a higher value for Area_tot and Area_trab at the 4% site (p < 0.05), no systematic bias was observed. The parallel-plate method yielded higher values for App.Tb.N and lower values for App.Tb.Th (p < 0.05), with no systematic bias. App.Tb.Sp values were smaller using the parallel-plate method, and the difference in methods increased as App.Tb.Sp values increased. Statistically, tolerance for repositioning around the 4% site of the radial bone is least for measures of bone area and greatest for BD_trab. On repeated measures, a proximal shift of 0.5 mm will not influence the results.     

Bone mineral density in hemodialysis patients with parathyroid dysfunction

We have determined bone mineral density (BMD) in hemodialysis patients with various parathyroid function in an attempt to elucidate the pathology of bone abnormalities, and obtained the following results. It is desirable that BMD (DXA) in the dialysis patients is determined at the radius rather than at the lumber spine. A higher BMD value might be obtained because of osteosclerosis of the vertebra or abdominal vascular calcification. The correlation between the SPA and the DXA was favorable in determining BMD at the distal one-third of the radius. The correlation between Jensen's classification based on subperiosteal resorption, intact-PTH, and BMD(radius) was favorable. The annual decrease in BMD was 4.0% and 4.7% in the male patients within 8 years and the female within 6 years after starting dialysis, respectively, and thier BMD decreased to 70 at above mentioned year. The annual BMD decrease became larger in the patients with severe 2'HPT, i.e., 7.1% in the male patients and 10.0% in the female patients. BMD after PTX markedly increased in the patients showing BMD of less than 70 at PTX. The BMD in one male patient who showed aluminium induced osteomalacia in past history was maintained at a relatively favorable value. The biochemical examination of two female patients who became an aparathyroid state after PTX showed improved values, but their BMD gradually decreased without showing any increase.     

Can bisphosphonate treatment be stopped in a growing child with skeletal fragility?

Summary

Cyclical pamidronate therapy in a 2-year-old child with skeletal fragility resulted in remodelling of vertebral fractures and improvement in bone mineral density (BMD) at distal radial and spinal sites. The BMD at both sites decreased precipitously within 24 months of stopping treatment, raising the question as to whether bisphosphonates can be stopped in a growing child with skeletal fragility.

Introduction

At age 23 months, a male toddler sustained a low trauma fracture of his right femur. Skeletal radiographs revealed generalised osteopenia with multiple vertebral body fractures. He was diagnosed with type IV osteogenesis imperfecta; however, no mutations were found in COL1A1 or COL1A2 genes.

Methods

This case report presents bone densitometry data before, during and after bisphosphonate treatment. Axial QCT was main outcome from 2 years of age; DXA and pQCT were taken after age 5.

Results

QCT confirmed that he had low spinal trabecular volumetric BMD (Z-score ?2.4). After 4 years of treatment his vertebral fractures had been remodelled and all bone densitometry values (QCT, DXA and pQCT) were within normal range and therefore treatment was discontinued. Shortly after this he suffered stress fractures of his left mid tibia and at the sclerotic metaphyseal line corresponding to his first APD treatment. He had marked reduction in spinal trabecular and distal radial vBMD; change in BMAD was less marked.

Conclusion

The patient has been restarted on IV APD therapy. This case has led us to consider whether bisphosphonate therapy can be discontinued in a child with fragility fractures before his/her linear growth has ceased?

     

pQCT bone strength index may serve as a better predictor than bone mineral density for long bone breaking strength

Bone mineral density (BMD) is commonly used to predict osteoporotic fracture risk without considering the geometry of the bone. However, geometric parameters are also important in determination of bone strength. An index including both material and geometric properties may be therefore more relevant in prediction of fracture risk. We studied the correlation between parameters measured by noninvasive peripheral quantitative computed tomography (pQCT) and bone bending strength of the diaphysis of 45 fresh goat humeri and 27 femora. Multislice pQCT was used for measuring volumetric diaphyseal cortical BMD, total BMD, diaphyseal and cortical cross-sectional area (CSA), and cross-sectional moment of inertia (CSMI) and their derived bone strength indices (BSIs), including BSI_CSMI (cortical BMD × CSMI) and BSI_CSA (cortical BMD × cortical CSA). Conventional dual-energy absorptiometry (DXA) was also conducted to measure areal BMD of diaphysis for comparison. Ultimate fracture load was obtained via three-point bending test. Results showed that for femora, fracture load was correlated better with BSI_CSA (r = 0.697, P 0.001) than cortical BMD (r = 0.304, P 0.05) and total BMD (r = 0.387, P 0.05) measured using pQCT and areal BMD (r = 0.612, P 0.001) measured using DXA. For humeri, fracture load was also correlated with BSI_CSA (r = 0.579, P 0.001) but not with other pQCT parameters including cortical BMD and total BMD (r = 0.282 and 0.305, respectively; P 0.05, both). The best correlation was found with areal BMD measured by DXA (r = 0.760, P 0.001). In conclusion, pQCT noninvasive BSI_CSA derived from cortical BMD (material) and its cortical CSA (bone geometry or distribution) may serve as an important noninvasive index for predicting long bone bending strength. The bending strength was also predicted by bone mass (areal BMD) measured by DXA, an integration of bone mineral and geometry. Further clinical studies are needed to validate the predictive value of BSI in long bone osteoporotic fracture.     

Quantitative Bone Mineral Assessment at the Forearm: A Review

Bone mineral density and geometric properties of the human forearm can be measured to determine the amount of bone or bone loss at the scanning site and to predict the risk of forearm fractures. These forearm mesurements are also used to estimate bone mass at remote anatomical locations and thereby estimate the risk for spine, hip and other fractures. The peripheral location of the human forearm, with its relatively small amount of surrounding soft tissue, improves the accuracy and the precision of bone mass measurement and has made this site an early choice for the assessment of a subject's bone mineral status. Furthermore, the anatomy of the human radius enables the examination of both cortical and cancellous bone. This review describes the procedures for non-invasive bone assessment at peripheral sites including some of the more recently developed systems dedicated to assessment of the distal radius. The accuracy, precision and normative values they provide are presented. Responses to different forms of therapies as well as the ability to discriminate or predict osteoporotic fractures are also assessed. Low radiation dose, comfortable and fast handling, moderate cost, and a strong association with the risk of non-spine fractures, promote the use of forearm scanning as a widely applied screening procedure for the detection of generalised osteoporotic bone loss. However, a higher accuracy of fracture risk prediction at the spine or at the hip can be achieved by a direct bone density measurement at these sites. The monitoring of treatment at the distal forearm appears to require a longer follow-up time due to its decreased responsiveness compared with such highly trabecular load-bearing sites as the spine and the proximal femur. Received: 4 August 1997 / Accepted: 13 November 1997     

Bone mineral density in children after renal transplantation

A successful kidney transplantation (Tx) offers good quality of life for children suffering from chronic renal failure. However, some metabolic abnormalities may not be corrected and may persist after Tx despite good graft function. Post-Tx bone disease seems to be a universal finding in adult Tx recipients, and is most probably related to steroids. Reports on bone mineral density (BMD) in children after renal Tx are not uniform. Recent studies suggest that BMD is normal when corrected for height. However, longitudinal studies show a transient decrease in BMD in the early post-Tx period. These controversial results raise the issue of the correct interpretation of dual-energy X-ray absorptiometry in children with stunted growth. Etiopathogenetic factors of the decreased BMD, preventive and thera- peutic measures are discussed. In conclusion, the results of dual energy X-ray absorptiometry should be interpreted with caution, especially in children with disturbed growth. Received: 3 May 1999 / Revised: 16 January 2000 / Accepted: 23 January 2000     

European semi-anthropomorphic spine phantom for the calibration of bone densitometers: Assessment of precision,stability and accuracy the European quantitation of osteoporosis study group

Up to now it has not been possible to reliably cross-calibrate dual-energy X-ray absorptiometry (DXA) densitometry equipment made by different manufacturers so that a measurement made on an individual subject can be expressed in the units used with a different type of machine. Manufacturers have adopted various procedures for edge detection and calibration, producing various normal ranges which are specific to each individual manufacturer's brand of machine. In this study we have used the recently described European Spine Phantom (ESP, prototype version), which contains three semi-anthropomorphic vertebrae of different densities made of simulated cortical and trabecular bone, to calibrate a range of DXA densitometers and quantitative computed tomography (QCT) equipment used in the measurement of trabecular bone density of the lumbar vertebrae. Three brands of QCT equipment and three brands of DXA equipment were assessed. Repeat measurements were made to assess machine stability. With the large majority of machines which proved stable, mean values were obtained for the measured low, medium and high density vertebrae respectively. In the case of the QCT equipment these means were for the trabecular bone density, and in the case of the DXA equipment for vertebral body bone density in the posteroanterior projection. All DXA machines overestimated the projected area of the vertebral bodies by incorporating variable amounts of transverse process. In general, the QCT equipment gave measured values which were close to the specified values for trabecular density, but there were substantial differences from the specified values in the results provided by the three DXA brands. For the QCT and Norland DXA machines (posteroanterior view), the relationships between specified densities and observed densities were found to be linear, whereas for the other DXA equipment (posteroanterior view), slightly curvilinear, exponential fits were found to be necessary to fit the plots of observed versus specified densities. From these plots, individual calibration equations were derived for each machine studied. For optimal cross-calibration, it was found to be necessary to use an individual calibration equation for each machine. This study has shown that it is possible to cross-calibrate DXA as well as QCT equipment for the measurement of axial bone density. This will be of considerable benefit for large-scale epidemiological studies as well as for multi-site clinical studies depending on bone densitometry.A Concerted Action of the European Community's COMAC-BME programme 1989–92. For further details of the Study Group see Appendix.     

Accuracy of peripheral quantitative computed tomography (pQCT) for assessing area and density of mouse cortical bone

Peripheral quantitative computed tomography (pQCT) is increasingly used for measurement of cortical bone geometry and density in mice. We evaluated the accuracy of pQCT for area and density measurements of thin-walled aluminum phantoms and mouse femora. Aluminum tubes with varying wall thicknesses and femora from 1- to 6-month-old C3H/HeJ (C3H) and C57B1/6J (B6) mice (average cortical thickness 0.14–0.29 mm) were scanned at 70- or 90-µm resolution. pQCT values of area were compared to optical values determined after sectioning, while pQCT density (vBMD) was compared to solid aluminum density or correlated to bone ash content. For the aluminum phantoms, the error in pQCT area and density depended strongly on wall thickness, and density was consistently underestimated. For mouse femora, threshold values were found that produced zero error in bone area for each strain and age group, although the optimal threshold differed between groups. pQCT vBMD correlated strongly with ash content (r² = 0.7), although the regression equations differed between strains and the magnitude of the inter-strain difference in vBMD was fourfold greater than the difference in ash content. This finding suggests that pQCT can overestimate the differences in volumetric mineral density between inbred mouse strains whose bones are of different thickness (e.g., C3H vs. B6). In conclusion, both area and density values obtained by pQCT depend strongly on specimen thickness, consistent with a partial volume averaging artifact. Investigators using pQCT to assess cortical bones in mice should be aware of the potential for cortical thickness-dependent errors.     

容积性定量CT测量股骨近端骨密度准确性研究

目的通过分别对比容积性定量CT(vQCT)、双能X射线吸收法(DXA)与灰化法测量股骨近端骨密度结果,确定并对比相关性,进行指导临床骨质疏松诊断及治疗。方法选取20个尸体股骨近端标本,先使用DXA骨密度仪扫描,测得骨矿含量(BMC)及骨密度(BMD)。再对标本相同部位行64层螺旋CT扫描,数据导入OsteoCAD软件自动分析得出骨密度值。应用灰化法得出标本灰质量密度。所有资料进行统计分析分别确定并对比vQCT及DXA测量的骨密度值与灰密度之间的相关性。结果vQCT测量股骨颈骨密度与灰质量密度线性相关性较好(r=0.852,P0.01),DXA与灰质量密度的相关性略差(r=0.807,P0.01)。结论vQCT测得的骨密度较DXA与灰质量密度线性相关性更好,可靠性高,对于诊断骨质疏松,预测骨质疏松性骨折,评价、指导骨质疏松骨折手术更有应用价值。     

Forearm BMD as measured by peripheral quantitative computed tomography (pQCT) in a German reference population

Low bone mass as estimated by decreased bone mineral density (BMD) is an established predictor of osteoporotic fractures. One of the latest developments in bone densitometry is peripheral quantitative computed tomography (pQCT) of the forearm. In Germany, the CT bone scanner XCT 900 has already been widely used; however, interpretation of measurements with respect to osteoporosis risk assessment can be improved by better defined and validated reference data. In the present study, this device was used to measure BMD at the distal radius in a well-defined healthy population of 179 German adults (91 men, 88 women) aged 20–79 years. In vivo precision was 1.67% for trabecular and 0.81% for total BMD measurements. Peak values of trabecular and total BMD were observed at the ages 40–50 years in women and 30–40 years in men. Beyond these ages, both trabecular and total BMD showed a linear decline with age, decreasing by 0.85% and 1.08% per year in women and by 0.59% and 0.54% in men, respectively. Measures of BMD were not influenced by weight, height or body mass index (BMI). In both sexes, trabecular and total radial BMD showed a positive and significant correlation with femoral BMD measures obtained by dual X-ray absorptiometry (DXA). Weaker correlations were observed with DXA measures of the lumbar spine. Compared with the 95% reference range provided by the manufacturer, the distribution of age- and sex-specific values of trabecular BMD of the distal radius was shifted to lower values by up to 1 standard deviation. Thus, 17% (30 of 179) of our apparently healthy population had BMD values falling short of the suggested lower reference limit. On the other hand, the distribution of total BMD values was shifted to higher values by up to 2 standard deviations in the younger age groups. We conclude that pQCT of the radius is a precise method for measuring BMD, but that its use for osteoporosis risk assessment crucially depends on both well-defined reference data and the results of prospective studies.     

Bone measures in HIV-1 infected children and adolescents: disparity between quantitative computed tomography and dual-energy X-ray absorptiometry measurements

Investigators have found that dual-energy X-ray absorptiometry (DXA) of areal bone mineral density (BMD) values in HIV-1 infected children and adolescents are reduced. Volumetric bone density (BD) measured by quantitative computed tomography (CT) in this population has not been studied. This study was designed to evaluate bone measurements in HIV-1 infected children and adolescents using DXA and CT. Fifty-eight children and adolescents (32 females and 26 males with a mean age ± SD of 12.0±3.9 years, age range 5.0–19.4 years) with perinatally acquired HIV-1 infection underwent simultaneous bone area and density evaluation by DXA and CT. Height and weight measurements as well as pubertal assessment were performed on the same day. All but four subjects were receiving highly active antiretroviral therapy (HAART). Subjects were matched with healthy children and adolescents for age, gender, and ethnicity. HIV-1 infected children were significantly shorter ( P <0.001), lighter ( P <0.005), and had delayed puberty ( P <0.001) compared to controls. Using DXA, HIV-1 infected subjects had significantly less bone area ( P <0.001), bone mineral content (BMC) ( P <0.005), and BMD ( P <0.05) at the vertebral level compared to controls. In addition, bone area ( P <0.001), BMC ( P <0.001), and BMD ( P <0.005) of the whole body were also reduced relative to controls. In contrast, using CT, HIV-1 infected subjects had similar vertebral BD compared to controls, but smaller vertebral height and cross-sectional area (CSA) ( P =0.01 and P <0.005, respectively). DXA Z-scores provided values significantly lower than CT Z-scores in the HIV-1 infected population ( P <0.01). After accounting for weight and vertebral height, stepwise multiple regression demonstrated that the prediction of CT BD values of L1 to L3 from DXA values of these vertebrae was significantly improved. HIV-1 infected children and adolescents have lower vertebral and whole body BMC and BMD DXA measures. In contrast, vertebral BD measurements by CT are normal. The lower bone measurements were primarily due to the decreased bone and body size of the HIV-1 subjects.This work was presented in part at the Pediatric Academic Society Annual Meeting, San Francisco, California, 1–4 May 2004.     

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.     

The effects of high potassium consumption on bone mineral density in a prospective cohort study of elderly postmenopausal women

Summary  Few studies have investigated the long-term effects of potassium intake on BMD. In a cohort of 266 elderly women, we found that baseline potassium intake as reflected by 24-hour urine potassium excretion had positive association with BMD measured at 1 and/or 5 years later, suggesting a role of dietary potassium on osteoporosis prevention. Introduction  High dietary potassium intake has been suggested to be beneficial for bone structure, but few studies have investigated the long-term effects of potassium intake on BMD in elderly women. We examined the relationship between potassium intake as reflected by 24-hour urine potassium excretion and bone density in a cohort of elderly women. Methods  The study subjects were 266 elderly postmenopausal women aged 70–80 years. Twenty-four-hour urinary potassium excretion was determined at baseline. At one year hip DXA BMD was measured, at 5 years hip and total body DXA BMD and distal radius and tibia pQCT vBMD were measured. The effects of potassium were evaluated by ANCOVA according to the quartile of baseline urinary potassium excretion. Results  After adjustment for confounding factors, subjects in the highest quartile of urinary potassium excretion had significantly higher total hip BMD at 1 (5%) and 5 years (6%), and significantly higher total body BMD (4%) and 4% distal tibia total (7%) and trabecular vBMD (11%) at 5 years than those in the lowest quartile. Conclusions  Potassium intake shows positive association with bone density in elderly women, suggesting that increasing consumption of food rich in potassium may play a role in osteoporosis prevention.     

Spinal bone mineral assessment in postmenopausal women: A comparison between dual X-ray absorptiometry and quantitative computed tomography

We compared quantitative computed tomography (QCT) and dual X-ray absorptiometry (DXA) with respect to their ability to discriminate subjects with and without prevalent vertebral fractures. In 240 post-menopausal women (mean age 63.7±6.9 years) lateral spine radiographs (T4-L4) were reviewed for the presence of vertebral fracture. Using a semiquantitative technique to grade the severity of vertebral deformities, we classified fractures as mild, moderate or severe (grade 1 to 3, respectively). Postero-anterior DXA (PA-DXA) and lateral DXA (L-DXA) measurements (L2–4) as well as QCT measurements of the lumbar spine (T12-L3 or L1–14) were obtained in all women. Seventy-two women were diagnosed with at least one fracture, and of these 40 were graded as mild. Comparing normal women with fractured women, we found the area under the receiver operating characteristics (ROC) curves to be greatest for QCT (0.81), followed by L-DXA (0.72) and PA-DXA (0.65). The differences among all three techniques were significant. Comparing the normal women with women having only mild fractures, the areas under the ROC curves were 0.79, 0.73 and 0.63 for QCT, L-DXA and PA-DXA, respectively. Significant differences existed between QCT and PA-DXA as well as between L-DXA and PA-DXA. Logistic regression analysis also revealed the highest age-adjusted odds ratios for QCT (3.67; 2.25–5.97) while L-DXA and PA-DXA showed substantially lower odds ratios (2.00; 1.39–2.87, and 1.54; 1.11–2.15, respectively). We conclude that low bone density as measured by QCT, PA-DXA or L-DXA is significantly associated with the prevalence of vertebral fractures. Of the methods studied, QCT of trabecular bone offered the best discriminatory capability. L-DXA proved to be superior to PA-DXA in its diagnostic sensitivity, particularly in women with mild fracture. Mild vertebral fractures are associated with decreased spinal bone density and may be regarded as osteoporotic deformities.     

Reproducibility of bone mineral density measurements using dual X-ray absorptiometry in daily clinical practice

Bone mineral density (BMD) measurements are frequently performed repeatedly for each patient. Subsequent BMD measurements allow reproducibility to be assessed. Previous studies have suggested that reproducibility may be influenced by age and clinical status. The purpose of the study was to examine the reproducibility of BMD by dual energy X-ray absorptiometry (DXA) and to investigate the practical value of different measures of reproducibility in three distinct groups of subjects: healthy young volunteers, postmenopausal women and patients with chronic rheumatic diseases. Two hundred twenty-two subjects underwent two subsequent BMD measurements of the spine and hip. There were 60 young healthy subjects, 102 postmenopausal women and 60 patients with chronic rheumatic diseases (33 rheumatoid arthritis, 10 ankylosing spondylitis and 10 other systemic diseases). Forty-five patients (75%) among the third group were receiving corticosteroids. Reproducibility was expressed as the smallest detectable difference (SDD), coefficient of variation (CV), least significant change (LSC) and intraclass correlation coefficient (ICC). Sources of variation were investigated by linear regression analysis. The median interval between measurements was 0 days (range 0–7). The mean difference (SD) between the measurements (g/cm²) was –0.0001 (±0.003) and –0.0004 (±0.002) at L1-L4 and the total hip, respectively. At L1-L4 and the total hip, SDD (g/cm²) was ±0.04 and ±0.02, CV (%) was 2.02 and 1.29, and LSC (%) 5.60 and 3.56, respectively. The ICC at the spine and hip was 0.99 and 0.99, respectively. Only a minimal difference existed between the groups. Reproducibility in the three groups studied was good. In a repeated DXA scan, a BMD change, the least significant change (LSC) or the SDD should be regarded as significant. Use of the SDD is preferable to use of the CV and LSC because of its independence from BMD and its expression in absolute units. Expressed as SDD, a BMD change of at least ±0.04 g/cm² at L1-L4 and ±0.02 g/cm² at the total hip should be considered significant. This reproducibility seems independent from age and clinical status and improved in the hips by measuring the dual femur.     

Bone density in white Brazilian women: Rapid loss at the time around the menopause

Dual energy x-ray absorptiometry (DXA) was used to measure bone mineral density (BMD) of the lumbar spine and proximal femur (neck, Ward's triangle, and trochanter) in 417 normal women (aged 20–79) living in São Paulo, Brazil. Bone density decreased with age at all sites. At the spine, the greatest decrease occurred during the sixth decade, with an average 11.4% bone loss compared with the previous decade. Stratifying the subjects according to menopausal status revealed that the fastest bone occurred at the time around the menopause (ages 45–60) when the rate of bone loss (-0.66%/year) was almost twice as rapid as in postmenopausal women (-0.39%/year). Although significant linear rates of bone loss were detected in all proximal femur sites before the menopause, a menopause-dependent pattern was less evident that at the spine. Lifetime rates of bone loss at the appendicular skeleton were-0.43,-0.62, and-0.35%/year at the femoral neck, Ward's triangle, and trochanteric area, respectively. After the menopause, BMD declined with menopausal age at all sites, although the rate of bone loss was faster at the femoral neck (-0.62%/year) and Ward's triangle (-0.84%/year) than at the spine-0.49%/year). The results are consistent with the notion that in women, the fastest bone loss occurs at the time round the menopause, most likely consequent to ovarian failure; and that faster rates of bone loss are detected at the proximal femur than at the lumbar spine in late postmenopausal women.     

Bone mineral density and turnover in patients with acromegaly in relation to sex, disease activity, and gonadal function

Acromegaly is a rare disease caused by growth hormone (GH) hypersecretion. GH and insulin-like growth factor-I (IGF-I) exert anabolic activity in bones. Nevertheless, bone mineral density (BMD) loss is not uncommon in patients with acromegaly. It is assumed to be due to hypogonadism associated with the acromegaly. The aim of the study was to examine BMD at various skeletal sites and bone turnover and to assess the influence of impaired gonadal function and disease activity on BMD and turnover changes in acromegaly. A total of 62 patients were studied (40 women, 22 men). Among the women, 22 had active disease and 18 were cured; 16 women had normal gonadal function, and 24 were hypogonadal. Altogether, 12 men presented with active acromegaly, and 10 were cured; normal gonadal function was found in 10 men, and hypogonadism was diagnosed in 12 men. Controls were 30 healthy subjects. Densitometry using dual-energy X-ray absorptiometry of the lumbar spine, proximal femur, forearm, and total body was carried out. Bone turnover was studied based on serum osteocalcin, C-terminal collagen type 1 crosslinks, and bone alkaline phosphatase concentration. A disadvantageous effect of acromegaly on bone density was associated with hypogonadism in the distal radius (in women), the proximal femur (in men), and the total body (both sexes). An anabolic effect of GH during active acromegaly was present in the proximal femur only in men. We confirmed increased bone turnover in the presence of acromegaly, and these changes were similar regarding the activity of the disease and the gonadal status.