Disorders of bone metabolism

Bone remodelling is critical to bone health. Alterations in the normal processes and regulation of remodelling may impact on bone mass and bone strength. Changes may be generalized or focal and underlie many of the common disorders of bone metabolism. This article focuses on the changes in bone remodelling which underlie both the development and treatment of osteoporosis. Osteomalacia, as an example of a mineralization disorder and Paget's disease as an example of a focal disorder of bone remodelling, are also briefly reviewed.     

晋城地区健康人群前臂骨峰值骨量的建立

目的：建立晋城地区健康人群前臂骨密度（ BMD）的峰值骨量和标准差值,为开展周围型双能X线骨密度仪测定及骨质疏松症研究提供基础数据。方法采用韩国产双能X线骨矿测量仪（ EXA－3000）对晋城地区1400例21～55岁的健康体检人群进行左侧前臂骨密度测定,进行非优势侧（左侧）前臂远端尺桡骨的BMD值测定,并分析其年龄分布,建立晋城地区健康人群前臂远端骨密度的峰值骨量和标准差值。骨质疏松的骨量诊断以骨量峰值的均数±标准差的形式建立,均数的计算采用三次方回归方程模型进行拟合。结果男、女性前臂骨的BMD值均符合正态分布,可采用均数±标准差（ xˉ±s）的形式表示。40岁以前男、女性前臂骨的BMD值均随年龄增加而逐步上升,且各年龄段BMD值的差异有统计学意义（P＜0．05）。45岁以后男、女性前臂骨的BMD值开始下降,且50岁以后下降明显（ P＜0．05）。男、女性前臂骨的骨量峰值均出现在41～45岁年龄段。男、女性前臂远端尺桡骨的骨量峰值及标准差分别为（0．5682±0．0647）g／cm2、（0．4209±0．0689）g／cm2。结论建立了晋城地区健康人群男、女性前臂骨的骨量峰值和标准差,为周围型双能X线骨密度仪测定并开展骨质疏松症的研究提供基础数据,尤其是用于高危人群筛查,以便确定是否需要进一步开展中轴骨测量或进行药物治疗。     

Regional Variation in the Denial of Reimbursement for Bone Mineral Density Testing Among US Medicare Beneficiaries

Although the Bone Mass Measurement Act outlines the indications for central dual-energy X-ray absorptiometry (DXA) testing for US Medicare beneficiaries, the specifics regarding the appropriate ICD-9 codes to use for covered indications have not been specified by Medicare and are sometimes ambiguous. We describe the extent to which DXA reimbursement was denied by gender and age of beneficiary, ICD-9 code submitted, time since previous DXA, whether the scan was performed in the physician's office and local Medicare carrier. Using Medicare administrative claims data from 1999 to 2005, we studied a 5% national sample of beneficiaries age ≥65 yr with part A + B coverage who were not health maintenance organization enrollees. We identified central DXA claims and evaluated the relationship between the factors listed above and reimbursement for central DXA (CPT code 76075). Multivariable logistic regression was used to evaluate the independent relationship between DXA reimbursement, ICD-9 diagnosis code, and Medicare carrier. For persons who had no DXA in 1999 or 2000 and who had 1 in 2001 or 2002, the proportion of DXA claims denied was 5.3% for women and 9.1% for men. For repeat DXAs performed within 23 mo, the proportion denied was approximately 19% and did not differ by sex. Reimbursement varied by more than 6-fold according to the ICD-9 diagnosis code submitted. For repeat DXAs performed at <23 mo, the proportion of claims denied ranged from 2% to 43%, depending on Medicare carrier. Denial of Medicare reimbursement for DXA varies significantly by sex, time since previous DXA, ICD-9 diagnosis code submitted, place of service (office vs facility), and local Medicare carrier. Greater guidance and transparency in coding policies are needed to ensure that DXA as a covered service is reimbursed for Medicare beneficiaries with the appropriate indications.     

Effects of skeletal size of the lumbar spine on areal bone density,volumetric bone density,and the diagnosis of osteoporosis in postmenopausal women in China

To understand the effects of skeletal size of the lumbar spine on areal bone mineral density (aBMD), volumetric bone mineral density (vBMD), and the diagnosis of osteoporosis in postmenopausal women, we measured the projected bone area, bone mineral content (BMC), aBMD, and vBMD at the anteroposterior and lateral lumbar spines in a population of 1081 postmenopausal Chinese women, 42 to 86 years of age. The results indicated that, at the anteroposterior and lateral lumbar spine, there were significant positive correlations between bone area and both BMC (r = 0.606; P = 0.000 and r = 0.610; P = 0.000) and aBMD (r = 0.270; P = 0.000 and r = 0.182; P = 0.000), but not vBMD (r = –0.055; P = 0.000 and r = 0.000; P = 0.929). When bone area at the anteroposterior spine changed by ±1 SD, the BMC, aBMD, and vBMD correspondingly changed by 28.2%, 10.1%, and 1.69% on the basis of their respective means. When a variation of ±1 SD was observed in bone area at the lateral spine, BMC and aBMD, correspondingly changed by 25.9% and 6.18% on the basis of their respective means, while vBMD indicated no change. Through comparisons among large-, intermediate-, and small-bone area groups, significant differences were found in the means of subjects heights, weights, BMC, and vBMD at the anteroposterior and lateral lumbar spines, as well as in the detection rates of osteoporosis by aBMD (P = 0.000). Detection rates of osteoporosis by aBMD at the anteroposterior spine and by aBMD at the lateral spine, and by vBMD were 44.1%, 55.5%, and 49.7%, respectively, in the total population; 31.4%, 41.7%, and 53.7%, respectively, in the large-bone area group; 43.3%, 55.9%, and 50.5%, respectively, in the intermediate-bone area group; and 61.7%, 70.0%, and 42.5%, respectively, in the small-bone area group. No significant differences were found in the detection rates of osteoporosis by vBMD among the groups. The results of multiple linear regression revealed that the major factors influencing skeletal size and aBMD of the lumbar spine were height and weight. Therefore, in menopausal women of the same ethnic group and age, the skeletal size of the lumbar spine would have significant influence upon aBMD and the diagnosis of osteoporosis, i.e., the larger the spinal size, the greater the aBMD and the lower the osteoporosis detection rate, while, conversely, the smaller the skeletal size, the smaller the aBMD and the higher the osteoporosis detection rate. When we use aBMD of the lumbar spine to diagnose osteoporosis in a population with different body sizes, we need to take this body size difference into account. When we use vBMD to diagnose osteoporosis, the effect of body size on BMD will diminish.     

Fracture Burden in Relation to Low Bone Mineral Density and FRAX Probability

Although the risk of fracture increases exponentially with declining bone mineral density, most fragility fractures have been shown to occur in individuals who do not meet the conventional densitometric definition for osteoporosis. The World Health Organization fracture risk assessment tool (FRAX^®) estimates individual 10-yr major osteoporotic and hip fracture probabilities. Intervention criteria based on risk assessment have been proposed by several groups, including the National Osteoporosis Foundation (NOF). We determined the relationship between 10-yr fracture probability and subsequent fracture burden in 36,730 women and 2873 men aged 50 yr and older. Using a major fracture probability cutoff of 20%, 29.4% of major osteoporotic fractures were identified in women and 4.9% in men. Based on a hip fracture probability cutoff of 3%, 54.1% of major osteoporotic fractures were detected in women and 53.4% in men. Using all NOF criteria, 65.9% of major osteoporotic fractures were detected in women and 69.3% in men. We conclude that men and women with FRAX probabilities below the high-risk NOF cutoffs have a high burden of major osteoporotic fractures. Strategies to enhance risk stratification in this group should be developed through international collaborations.     

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

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

Measurement of bone mineral density of lumbar spine and whole body in low-birth-weight infants: comparison of two methods

In the present study, we compared lumbar spinal and whole-body bone mineral density (BMD) measurements to determine which is more suitable for evaluating the bone mineral status of low-birth-weight (LBW) infants. Lumbar spinal and whole-body BMD were assessed simultaneously in a prospective series including 152 Japanese LBW infants (birth weight 453–2400 g, gestational age 24–38 weeks) from the age of 40 weeks post-conception to 2 years of age. Lumbar spinal BMD at 40 weeks post-conception was significantly correlated with birth weight (r = 0.74; P < 0.0001), but whole-body BMD was not correlated with birth weight. No correlation was found between lumbar spinal and whole-body BMD at 40 weeks post-conception. However, after 40 weeks post-conception, a significant correlation was found between lumbar spinal and whole-body BMD (r = 0.65; P < 0.0001). For infants with a body weight of 4 kg or less at the time of measurement, no correlation was found between lumbar spinal and whole-body BMD. However, for infants with a body weight above 4 kg, a significant correlation was found between lumbar spinal and whole-body BMD (r = 0.65; P < 0.0001). Thus, lumbar spinal BMD is more suitable than whole-body BMD for evaluation of the bone mineral status of LBW in early infancy. Therefore, lumbar spinal BMD should be used for serial evaluation of changes in the bone mineral status of LBW infants. Received: April 6, 2000 / Accepted: June 16, 2000     

Consistency of low bone density across bone sites in SAMP6 laboratory mice

The development of bone densitometry has made it clear that there are discrepancies in bone density at various measurement sites in a given individual. This study examined the consistency of bone density measurements across various sites in a strain of laboratory mouse (senescence-accelerated mouse; SAM). A systemic evaluation of the bone density was performed by dual-energy X-ray absorptiometry (DXA) on SAMP6 (P6) mice, a strain with low peak bone density, as measured by microphotodensitometry of the femoral bones, whereas the SAMP2 (P2) and SAMR1 (R1) strains have high peak bone density. We modified Jilkas method to more comprehensively measure the whole body and additional regions of interest (ROIs; head, right foreleg, left foreleg, right hindleg, left hindleg, spine, and tail). The age-related changes in the total (whole-body) BMD showed a common pattern among the strains studied, and the peak value was seen at 4 months old. P6 showed the lowest peak BMD. A detailed comparison of the bone density between P6 and P2 at the age of 4 months revealed significantly lower regional BMD values for P6 in all seven ROIs. The strain difference in BMD could not be attributed to a difference in size. In conclusion, P6 mice showed low bone density not only in their femurs but also in the subregions and over their entire body. This strain can be potentially useful in the investigation of the genetic basis of senile osteoporosis.     

Bone loss after kidney transplantation: a longitudinal study in 115 graft recipients

BACKGROUND.: Bone loss is an important problem in renal transplant recipientsimmediately after surgery. No data are available about the boneloss beyond the first post-transplantation year. METHODS.: In a longitudinal, uncontrolled observational study bone mineraldensity (BMD) was measured by dual X-ray absorptiometry in 115renal graft recipients starting at different times after transplantation(0–20 years after transplantation) with a follow-up timeof 12 months. RESULTS.: A total of 56 patients showed a reduction of BMD during theobservation period. Bone loss depended on the time after transplantation.Mean reduction of BMD at lumbar spine was 7±10%, 1±9%during the first and second postoperative year. Beyond the thirdyear bone mineral density did not change or even increased slightly(0±4% during 3–5th year, 1±6% during 6–10thyear and 2±4% during 11–20th year after transplantation).Decrease of BMD correlated with a higher mean daily prednisonedosage (P<0.001), a higher cumulative prednisone dose (P<0.01),a more frequent and more steroid-resistant rejection (P<0.001)and a higher initial parathyroid hormone level (P<0.001).Patients with 25-OH-cholecalciferol therapy (P<0.05) or morephysical activity (P<0.05) had a smaller bone loss. CONCLUSIONS.: Reduction of BMD after transplantation is highest within thefirst post-transplant year. The effects of acute graft rejection,prednisone dosage and initial parathyroid hormone level arepredominant among the multiple factors associated with pronouncedbone loss.     

上海地区女性前臂骨峰值骨量的建立及其影响因素研究

目的 建立女性前臂骨不同测量部位的峰值骨量和标准差值,并探讨其可能影响因素,为周围型DEXA测定开展OP研究提供基础数据.方法 对上海市区365例21～59岁社区女性健康志愿者,采用美国NORLAND-Stratec周围型双能X线骨矿测量仪(pDEXA)测量了非优势侧(左侧)前臂远端桡骨和尺骨(Distal radius and ulna, Dist. R+U)、近端桡骨和尺骨(Proximal radius and ulna, Prox. R+U)和近端桡骨(Proximal radius, Prox. R)的BMD值,并分析了其年龄分布,建立了女性前臂骨不同测量部位的峰值骨量和标准差值.同时,以问卷调查了可能影响因素.结果 前臂骨各部位的BMD值均符合正态分布,可以采用均数±标准差(x±s)的形式表示,OP的骨量诊断标准也可以用骨量峰值的算术均数降低标准差的形式建立.45岁以前女性前臂骨不同测量部位的BMD值均随年龄增加而逐步上升,但不同年龄段BMD值的差异并不显著(P>0.05),45岁以后BMD值明显下降.前臂骨不同测量部位的骨量峰值均出现在40～44岁年龄段,前臂远端桡+尺骨(Dist. R+U)、近端桡+尺骨(Prox. R+U)和近端桡骨(Prox. R)的骨量峰值及标准差分别为(0.3717±0.0423) g/cm~2、(0.7958±0.0771) g/cm~2和(0.7802±0.0671) g/cm~2.此外,体重和怀孕次数对峰值骨量的形成有较大影响,体重过轻和怀孕次数过多均不利于峰值骨量的形成.结论 建立女性前臂骨不同部位的骨量峰值和标准差,可为周围型DEXA测定开展OP研究提供基础数据,尤其是用于高危人群筛查以确定是否需进一步开展中轴骨测量或进行药物干预.     

Assessment of Bone Mineral Density at the Distal Femur and the Proximal Tibia by Dual-Energy X-ray Absorptiometry in Individuals With Spinal Cord Injury: Precision of Protocol and Relation to Injury Duration

Spinal cord injury (SCI) is characterized by marked bone loss at the knee, and there is a need for established dual-energy X-ray absorptiometry (DXA) protocols to examine bone mineral density (BMD) at this location to track therapeutic progress and to monitor fracture risk. The purpose of this study was to quantify the precision and reliability of a DXA protocol for BMD assessment at the distal femur and the proximal tibia in individuals with SCI. The protocol was subsequently used to investigate the relationship between BMD and duration of SCI. Nine individuals with complete SCI and 9 able-bodied controls underwent 3 repeat DXA scans in accordance with the short-term precision methodology recommended by the International Society of Clinical Densitometry. The DXA protocol demonstrated a high degree of precision with the root-mean-square standard deviation ranging from 0.004 to 0.052?g/cm² and the root-mean-square coefficient of variation ranging from 0.6% to 4.4%, depending on the bone, the region of interest, and the rater. All measurements of intra- and inter-rater reliability were excellent with an intraclass correlation of ≥0.950. The relationship between the BMD and the duration of SCI was well described by a logarithmic trend (r²?=?0.68–0.92). Depending on the region of interest, the logarithmic trends would predict that, after 3?yr of SCI, BMD at the knee would be 43%–19% lower than that in the able-bodied reference group. We believe the DXA protocol has the level of precision and reliability required for short-term assessments of BMD at the distal femur and the proximal tibia in people with SCI. However, further work is required to determine the degree to which this protocol may be used to assess longitudinal changes in BMD after SCI to examine clinical interventions and to monitor fracture risk.     

Radiolucent Casting Tape Allows for Accurate Measurement of Forearm Bone Mineral Density Using Dual-Energy X-ray Absorptiometry

The ability to perform dual-energy X-ray absorptiometry (DXA) while a patient is in a cast would give investigators the opportunity to follow early changes in bone mineral density (BMD, g/cm2) during fracture healing or to evaluate bone changes related to immobilization. The objective of this study was to determine if accurate and precise DXA scans could be obtained through polyester-based radiolucent casting tape (Delta-Cast Elite [DCE], Johnson & Johnson, Inc., Raynham, MA) and standard fiberglass casting tape (Delta Lite [DL], Johnson & Johnson, Inc.). DXA scans were performed using a Lunar DPXL densitometer. Standard forearm regions of interest were analyzed. Ten normal volunteers had three consecutive scans of their dominant arm with no cast, with a radiolucent (DCE) cast, and with a fiberglass (DL) cast. Precision was calculated using data from three volunteers (three scans each; no cast, DCE, DL). Results of DCE and DL were compared with results with no cast. In a second series, a spine phantom was placed inside rice-filled forearm casts and repetitively scanned; results with DCE and DL were compared with the mean BMD values for the phantom alone. Analyses of the scans through the DL casts were difficult because the radiodensity of the fiberglass interfered with edge detection. This problem was exacerbated by low BMD (i.e., scans for women). Edge detection was not a problem with the DCE scans. Although the group mean BMD values with in vivo no cast, DCE, or DL scans were similar for all regions of interest, the data obtained for ultradistal regions of interest with DL scans were less precise. BMD values for the fiberglass-encased phantom were significantly lower compared with no cast or DCE scans (p = 0.0002). This study demonstrates that it is possible to perform accurate and precise forearm DXA scans through polyester-based radiolucent DCE casting tape.     

Prevalence of osteoporosis and reference data for lumbar spine and hip bone mineral density in a Korean population

The aims of this study were to establish reference data for bone mineral density (BMD) at central skeletal sites using Lunar dual-energy X-ray absorptiometry (DXA), and to estimate the age-and sex-specific prevalence of osteoporosis in a Korean population. We performed a population-based, cross-sectional study. The subjects were 4148 (1810 men and 2338 women) Korean adults, aged 20–79 years. The BMD for central sites (lumbar spine, femoral neck, trochanter, and Ward’s triangle) were measured by DXA. The standardized prevalence of osteoporosis among individual aged 50–79 years in lumbar spine, femoral neck, Ward’s triangle, and trochanter was 40.1%, 12.4%, 28.4%, and 4.4% in women and 6.5%, 5.9%, 3.7%, and 1.6% in men, respectively. In women, peak BMD occurred in the age range 40–49 years for the femoral neck and trochanter, 30–39 years for the lumbar spine, and 20–29 years for Ward’s triangle. In men, peak BMD values were observed at 20–29 years for all measured sites. This study establishes a normative database for BMD at central skeletal sites using dualenergy X-ray absorptiometry and provides more reliable information on the prevalence of osteoporosis in Korea.     

北京地区3859名体检人群骨密度调查及骨量异常患病率分析

目的调查北京地区健康体检人群骨密度的情况以及骨量减少和骨质疏松的患病率,为骨质疏松症的防治提供参考。方法选择2017年1月至2018年12月在中日友好医院健康体检中心进行健康体检的人群,排除继发性骨质疏松症及其他影响骨代谢的因素,共3859名。其中男性2067名,女性1792名。年龄20~83岁,平均年龄(51.29±11.18)岁,按性别及年龄每10年一组。采用美国GE公司的LUNAR Prodigy双能X线骨密度仪测量受试者腰椎1~4正位及股骨颈和全髋的骨密度。分析各组不同部位骨密度情况及骨量异常(包括骨量减少和骨质疏松)的患病率。采用SPSS 22.0统计软件进行分析,以P<0.05为差异有统计学意义。结果①男性腰椎1~4骨密度峰值在20~29岁,股骨颈和全髋骨密度峰值在30~39岁。女性各部位骨密度峰值均在30~39岁。②随年龄增长,男性和女性骨量异常患病率均呈上升趋势,50岁以上女性骨量异常患病率显著上升,明显高于同年龄组男性。③30~59岁男性和女性腰椎骨量异常患病率均明显高于髋部;70岁以上男性和60岁以上女性髋部骨量异常患病率明显高于腰椎。结论中老年人群尤其是绝经后女性是骨质疏松症的高危人群;老年人群的骨质疏松筛查可以考虑选择髋部骨密度为主。     

Dual-Energy X-Ray Absorptiometry Interpretation and Reporting in Children and Adolescents: The Revised 2013 ISCD Pediatric Official Positions

The International Society for Clinical Densitometry Official Revised Positions on reporting of densitometry results in children represent current expert recommendations to assist health care providers determine which skeletal sites should be measured, which, if any, adjustments should be made, reference databases to be used, and the elements to include in a dual-energy X-ray absorptiometry report. The recommended scanning sites remain the total body less head and the posterior-anterior spine. Other sites such as the proximal femur, lateral distal femur, lateral vertebral assessment, and forearm are discussed but are only recommended for specific pediatric populations. Different methods of interpreting bone density scans in children with short stature or growth delay are presented. The use of bone mineral apparent density and height-adjusted Z-scores are recommended as suitable size adjustment techniques. The validity of appropriate reference databases and technical considerations to consider when upgrading software and hardware remain unchanged. Updated reference data sets for all contemporary bone densitometers are listed. The inclusion of relevant demographic and health information, technical details of the scan, Z-scores, and the wording “low bone mass or bone density” for Z-scores less than or equal to −2.0 standard deviation are still recommended for clinical practice. The rationale and evidence for the development of the Official Positions are provided. Changes in the grading of quality of evidence, strength of recommendation, and worldwide applicability represent a change in current evidence and/or differences in opinion of the expert panelists used to validate the position statements for the 2013 Position Development Conference.     

Reduction of bone mineral density in rheumatoid arthritis: A longitudinal study

In the last decade, more accurate quantitative methods to assess bone mass in vivo have become available. We have applied these techniques to assess periodic changes of bone loss in rheumatoid arthritis (RA) patients. In this longitudinal study, 132 female RA patients were divided into two groups. The first group of 90 patients were postmenopausal, with a mean age of 60.2 years (PM group), whereas the second group of 42 patients were premenopausal, with a mean age of 42.7 years (M group). The clinical courses of these patients were followed for an average of 3 years. Bone mineral density (BMD) in the lumbar spine (L2–L4), and the femoral neck were measured by dual-energy X-ray absorptiometry (DXA), and second metacarpal bone mineral density was measured by using densitometric techniques periodically. Reduction of BMD in the lumbar spine was significant in both groups (P<0.01–0.05), but there was no statistical difference between the two groups. The BMD of the femoral neck had a tendency to decrease but this was not significant. The predictors for periodic bone loss in the PM group were aging and nutritional factors, whereas for the M group they were indices of rheumatoid arthritis disease activity.     

An evaluation of the United Kingdom National Osteoporosis Society position statement on the use of peripheral dual-energy X-ray absorptiometry

A recent position statement issued by the UK National Osteoporosis Society recommends a triage approach to the use of peripheral dual-energy X-ray absorptiometry (pDXA) devices. Patients with a forearm T-score greater than –1 or less than –2.5 are regarded as normal or osteoporotic, respectively, while those with a T-score between –1 and –2.5 are sent for further assessment with spine and hip DXA. We have evaluated the NOS pDXA algorithm by comparing it with the alternative strategies of relying on forearm BMD alone, or performing spine and hip DXA in every patient. The evaluation was carried out using a mathematical model, and the predictions were compared with in vivo data obtained in patients referred for investigation by their general practitioner. In the model the population distribution of spine, hip, and forearm BMD was described by a trivariant Gaussian function. Relative risks of fracture were taken from a meta-analysis. The three strategies were compared using receiver operating characteristic (ROC) curves in which the percentage of future fracture cases identified was plotted against the percentage of the whole population found to have osteoporosis. ROC curves plotted for the discrimination of hip, vertebral, and Colles fracture risk and the risk of a fracture at any skeletal site were similar for all three strategies, with the curves for the NOS pDXA algorithm nearly identical to those for spine and hip DXA. For the case of hip fracture, vertebral fracture, or a fracture at any site, forearm BMD was slightly inferior to the NOS algorithm, but the reverse was true for Colles fracture. The small difference between the ROC curves suggests that forearm BMD used alone can reproduce clinical decision-making with the NOS pDXA algorithm provided that a T-score threshold of T=–2.1 is used for the diagnosis of osteoporosis, instead of the conventional figure of T=–2.5. Results from the in vivo study were in good agreement with the predictions of the model, although some differences were observed that were explained by inaccuracies in the forearm reference data. We conclude that use of forearm BMD alone with a modified T-score threshold of –2.1 would save the need for spine and hip DXA scans and identify only slightly fewer fracture cases for treatment.     

Spine-Hip T-Score Difference Predicts Major Osteoporotic Fracture Risk Independent of FRAX: A Population-Based Report From CAMOS

The WHO fracture risk assessment tool (FRAX^®) estimates an individual’s 10-yr major osteoporotic and hip fracture probabilities. When bone mineral density (BMD) is included in the FRAX calculation, only the femoral neck measurement can be used. Recently, a procedure was reported for adjusting major osteoporotic fracture probability from FRAX with femoral neck BMD based on the difference (offset) between the lumbar spine and the femoral neck T-score values. The objective of the current analysis was to independently evaluate this algorithm in a population-based cohort of 4575 women and 1813 men aged 50 yr and older from the Canadian Multicentre Osteoporosis Study. For women and men combined, there was a 15% (95% confidence interval 7–24%) increase in major osteoporotic fracture risk for each offset T-score after adjusting for FRAX probability calculated with femoral neck BMD. The effect was stronger in women than men, but a significant sex interaction was not detected. Among the full cohort, 5.5% had their risk category reclassified after using the offset adjustment. Sex- and age-dependent offsets (equivalent to an offset based on Z-scores) showed improved risk classification among individuals designated to be at moderate risk with the conventional FRAX probability measurement. In summary, the T-score difference between the lumbar spine and femoral neck is an independent risk factor for major osteoporotic fractures that is independent of the FRAX probability calculated with femoral neck BMD.     

BMD Reference Standards Among South Asians in the United States

The relationship between bone mineral density (BMD) and fracture risk is not well established for non-white populations. There is no established BMD reference standard for South Asians. Dual-energy X-ray absorptiometry (DXA) was used to measure BMD at total hip and lumbar spine in 150 US-based South-Asian Indians. For each subject, T-scores were calculated using BMD reference values based on US white, North Indian, and South Indian populations, and the resulting WHO BMD category assignments were compared. Reference standards derived from Indian populations classified a larger proportion of US-based Indians as normal than did US white-based standards. The percentage of individuals reclassified when changing between reference standards varied by skeletal site and reference population origin, ranging from 13% (95% confidence interval [CI]: 7–18%), when switching from US white- to North Indian-based standard for total hip, to 40% (95% CI: 32–48%), when switching from US white to South Indian reference values for lumbar spine. These findings illustrate that choice of reference standard has a significant effect on the diagnosis of osteoporosis in South Asians, and underscore the importance of future research to quantify the relationship between BMD and fracture risk in this population.