Apparent bone mineral density estimated from DXA in healthy men and women

The aim of this study was to measure bone mineral density (BMD) in healthy people and examine the influence of age, anthropometry, and postmenopause on calculated bone mineral apparent density (BMAD). The study included 541 healthy subjects (249 men and 292 women), aged 20 to 79 years. Anthropometric measurements included height, weight, and body mass index (BMI). Bone mineral content (BMC) and areal BMD were measured at the lumbar spine and proximal femur, using dual-energy X-ray absorptiometry (DXA). The calculation of volumetric density relied on the formula BMAD=BMD/BA (where BA = bone area). Association between densitometric parameters and age, height, weight, and postmenopause was analyzed with multiple regression. BMC and BMD decreased with age, especially in postmenopausal women. The average annual bone loss in spine was 0.2% in both sexes, whereas femur loss was 0.5% in men and 0.3% in women. Bone area slightly increased with age in both sexes, and BMD loss after the age of 50 could be attributed to bone area increase. To minimize the effect of bone size on bone density, volumetric density and areal density were regressed to age, anthropometry, and postmenopause. Age and postmenopause were significantly associated with BMD and BMAD in the spine and femur. Furthermore, BMD showed a stronger association with height and weight than BMAD, in both regions. Weaker association of body height and weight with BMAD than with BMD suggests that BMD depends on the bone size and body size and that the different BMDs could be the consequence of the difference in those parameters.     

Bone density interpretation and relevance in Caucasian children aged 9-17 years of age: insights from a population-based fracture study.

The interpretation of bone density measurement in children is difficult due to a number of factors including rapid change in body size and uncertain clinical significance of bone density in children. This study asked two questions. (1) Is there a preferred bone density measurement site or type for fracture risk in children? (2) What is the best way to interpret bone density in children? This population-based case control study included 321 upper limb fracture cases and 321 class- and sex- matched randomly selected controls. Bone density at the hip, spine, and total body (including the arm) was measured by a Hologic QDR2000 densitometer (Waltham, MA) and examined as bone area (BA), bone mineral content (BMC), bone mineral density (BMD), bone mineral apparent density (BMAD), and BMC/lean mass (BMCLM). The only dual-energy X-ray absorptiometry (DXA) variables that were consistently associated with fracture risk in both boys and girls were spine BMD and BMAD for total upper limb fractures, and spine and hip BMAD for wrist and forearm fractures. No significant associations were observed for BA and BMCLM and inconsistent associations for BMC and other BMD sites. Five-yr fracture risk varied from 15–24% depending on site and gender in a child with a Z-score of -3. In the controls, all DXA variables were associated with age, height, and weight, but the weakest associations were with BMAD. In conclusion, in this study the spine BMAD had the strongest and most consistent association with upper limb fracture risk in children. The associations with age and body size imply that age specific Z-scores will be the most convenient for interpretation of DXA measures in children. Five-yr wrist and forearm fracture risk has potential as a clinical endpoint of immediate relevance.     

DXA estimates of vertebral volumetric bone mineral density in children: potential advantages of paired posteroanterior and lateral scans.

Dual-energy X-ray absorptiometry (DXA) estimates of areal bone mineral density (BMD) are confounded by bone size in children. Two strategies have been proposed to estimate vertebral volumetric BMD: (1) bone mineral apparent density (BMAD) is based on the posteroanterior (PA) spine scan; (2) width-adjusted bone mineral density (WABMD) is based on paired PA lateral scans. The objective of this study was to compare DXA estimates of vertebral bone mineral content (BMC), volume and volumetric BMD obtained from Hologic PA scans (Hologic, Inc., Bedford, MA) alone, and paired PA lateral scans in 124 healthy children, ages 4 to 20 yr. The PA scans were used to estimate bone volume (PA Volume) as (PA Area)1.5 and BMAD as [(PA BMC)/(PA Volume)]. Paired PA lateral scans were used to estimate width-adjusted bone volume (WA Volume) as [(pi/4)(PA width)(lateral depth)(vertebral height)] and WABMD as [(lateral BMC)/(WA Volume)]. Generalized estimating equations were used to compare the relationship between scan type (PA vs. paired PA lateral) and bone outcomes, and the effects of height and maturation on this relationship. The estimates of BMC and volume derived from PA scans and paired PA lateral scans were highly correlated (r>0.97); WABMD and BMAD were less correlated (r=0.81). The increases in BMC, volume, and volumetric BMD with greater height and maturation were significantly larger (all p<0.001) when estimated from paired PA lateral scans, compared with PA scans alone. The proportion of spine BMC contained within the vertebral body, versus the cortical spinous processes, increased significantly with age (p<0.001) from 28% to 69%. The smaller increases in bone measures on PA scans may have been due to magnification error by the fan beam as posterior tissue thickness increased in taller, more mature subjects, and the distance of the vertebrae from the X-ray source increased. In conclusion, paired Hologic PA lateral scans may increase sensitivity to growth-related increases in trabecular BMC and density in the spine, with less bias due to magnification error.     

Bone mineral density and prevalent vertebral fractures in men and women

To test the hypothesis that the association between bone mineral density (BMD) and estimated volumetric BMD and prevalent vertebral fractures differs in men and women, we studied 317 Caucasian men and 2,067 Caucasian women (average age 73 years). A total of 43 (14%) men and 386 (19%) women had a vertebral fracture identified on lateral spine radiographs using vertebral morphometry. Hip and spine areal BMD was about 1/3 standard deviation lower among men and women with a vertebral fracture. A 0.10 g/cm² decrease in areal BMD was associated with 30–40% increased odds of having a fracture in men and 60–70% increased likelihood in women. Low bone mineral apparent density (BMAD) was also associated with 40–50% increased odds of a vertebral fracture in both genders. The probability of a man having a fracture was observed at higher absolute areal BMD values than observed for women (P=values for interaction of BMD × gender: trochanter, P=0.05; femoral neck, P=0.10; total hip, P=0.09). In contrast, the probability of fracture was similar in men and women across the range of estimated volumetric BMD (BMAD). In conclusion, low BMD and low BMAD are associated with increased odds of vertebral fracture in both men and women. Measures of bone mass that partially correct for gender differences in bone size may yield universal estimates of fracture risk. Prospective studies are needed to confirm this observation.     

Interpretation of whole body dual energy X-ray absorptiometry measures in children: comparison with peripheral quantitative computed tomography

The assessment of bone health in children requires strategies to minimize the confounding effects of bone size on dual energy X-ray absorptiometry (DXA) areal bone mineral density (BMD) results. Cortical bone composes 80% of the total skeletal bone mass. The objective of this study was to develop analytic strategies for the assessment of whole body DXA that describe the biomechanical characteristics of cortical bone across a wide range of body sizes using peripheral quantitative computed tomography (pQCT) measures of cortical geometry, density (mg/mm³), and strength as the gold standard. Whole body DXA (Hologic QDR 4500) and pQCT (Stratec XCT-2000) of the tibia diaphysis were completed in 150 healthy children 6–21 years of age. To assess DXA and pQCT measures relative to age, body size, and bone size, gender-specific regression models were used to establish z scores for DXA bone mineral content (BMC) for age, areal BMD for age, bone area for height, bone area for lean mass, BMC for height, BMC for lean mass, and BMC for bone area; and for pQCT, bone cross-sectional area (CSA) for tibia length and bone strength (stress-strain index, SSI) for tibia length. DXA bone area for height and BMC for height were both strongly and positively associated with pQCT CSA for length and with SSI for length (all P < 0.0001), suggesting that decreases in DXA bone area for height or DXA BMC for height represent narrower bones with less resistance to bending. DXA BMC for age (P < 0.01) and areal BMD (P < 0.05) for age were moderately correlated with strength. Neither DXA bone area for lean mass nor BMC for lean mass correlated with pQCT CSA for length or SSI for length. DXA BMC for bone area was weakly associated with pQCT SSI for length, in females only. Therefore, normalizing whole body DXA bone area for height and BMC for height provided the best measures of bone dimensions and strength. DXA BMC normalized for bone area and lean mass were poor indicators of bone strength.     

Interpretation of calcaneus dual-energy X-ray absorptiometry measurements in the assessment of osteopenia and fracture risk.

Dual-energy X-ray absorptiometry (DXA) of the calcaneus is useful in assessing bone mass and fracture risk at other skeletal sites. However, DXA yields an areal bone mineral density (BMD) that depends on both bone apparent density and bone size, potentially complicating interpretation of the DXA results. Information that is more complete may be obtained from DXA exams by using a volumetric density in addition to BMD in clinical applications. In this paper, we develop a simple methodology for determining a volumetric bone mineral apparent density (BMAD) of the calcaneus. For the whole calcaneus, BMAD = (BMC)/ADXA3/2, where BMC and ADXA are, respectively, the bone mineral content and projected area measured by DXA. We found that ADXA3/2 was proportional to the calcaneus volume with a proportionality constant of 1.82 +/- 0.02 (mean +/- SE). Consequently, consistent with theoretical predictions, BMAD was proportional to the true volumetric apparent density (rho) of the bone according to the relationship rho = 1.82 BMAD. Also consistent with theoretical predictions, we found that BMD varied in proportion to rho V1/3, where V is the bone volume. We propose that the volumetric apparent density, estimated at the calcaneus, provides additional information that may aid in the diagnosis of osteopenia. Areal BMD or BMD2 may allow estimation of the load required to fracture a bone. Fracture risk depends on the loading applied to a bone in relation to the bone's failure load. When DXA is used to assess osteopenia and fracture risk in patients, it may be useful to recognize the separate and combined effects of applied loading, bone apparent density, and bone size.     

Differences in bone mineral density,bone mineral content,and bone areal size in fracturing and non-fracturing women,and their interrelationships at the spine and hip

Osteoporotic fractures are a major public health problem, particularly in women. Bone mineral density (BMD), bone mineral content (BMC), and bone size have been regarded as important determinants of osteoporotic fractures. In 1449 women over age 30 years, we studied the detailed relationship, at the spine and hip, between BMD, BMC, and bone areal size (all measured by dual-energy X-ray absorptiometry) and compared their relative magnitudes in fracturing and non-fracturing individuals. We find that, (1) BMD and BMC are significantly higher at the spine and hip in non-fracturing women. Bone areal size is significantly larger at the spine in non-fracturing women; however, the significance disappears when adjustment is made for the significant difference of height (stature) between fracturing and non-fracturing women. In contrast to the spine, bone areal size is always significantly largerin fracturing women at the hip. (2) The relationship among BMD, BMC, and bone areal size is different at the spine and hip. Specifically, at the spine, BMD increases with bone areal size linearly. At the hip, BMD has a quadratic relationship with bone areal size, so that BMD increases at lower bone areal sizes, then (after an intermediate zone of values) decreases with increasing bone areal size. However, BMD adjusted for BMC always decreases with increasing bone areal size, as expected by the definition of BMD. With no adjustment for BMC, the increase in BMD with bone areal size is due to a more rapid increase of BMC than increasing bone areal size, thus explaining the observations of association of both larger BMD and larger bone areal size with stronger bone. (3) At the spine, 86.2% of BMD variation is attributable to BMC and 12.6% to bone areal size. At the hip, 98.0% of BMD variation is due to BMC and 1.1% due to bone areal size. The current study may be important in understanding the relationship among BMD, BMC, and bone size as risk determinants of osteoporotic fractures.     

Birth weight is an independent determinant of whole body bone mineral content and bone mineral density in a group of Lebanese adolescent girls

The aim of this study was to explore the relation between birth weight and bone mass in a group of adolescent girls. This study included 40 post-menarchal adolescent (aged 13–20 years) girls. Anthropometric characteristics (height and weight) were measured and birth weights were obtained from the obstetric records. Body composition, bone mineral content (BMC) and bone mineral density (BMD) of the whole body (WB) were assessed by dual-energy X-ray absorptiometry (DXA). Calculations of the ratio BMC/height and of the bone mineral apparent density (BMAD) were completed for the WB. Birth weight was positively correlated to BMC and to the ratio BMC/height even after adjusting for weight and maturation index (years since menarche). Finally, birth weight was correlated to BMD even after adjusting for weight. In conclusion, this study suggests that birth weight is an independent determinant of whole body BMC and BMD in adolescent girls.     

Diagnostic evaluation of bone densitometric size adjustment techniques in children with and without low trauma fractures

Summary

Several established methods are used to size adjust dual-energy X-ray absorptiometry (DXA) measurements in children. However, there is no consensus as to which method is most diagnostically accurate. All size-adjusted bone mineral density (BMD) values were more diagnostically accurate than non-size-adjusted values. The greatest odds ratio was estimated volumetric BMD for vertebral fracture.

Introduction

The size dependence of areal bone density (BMD_a) complicates the use of DXA in children with abnormal stature. Despite several size adjustment techniques being proposed, there is no consensus as to the most appropriate size adjustment technique for estimating fracture risk in children. The aim of this study was to establish whether size adjustment techniques improve the diagnostic ability of DXA in a cohort of children with chronic diseases.

Methods

DXA measurements were performed on 450 children, 181 of whom had sustained at least one low trauma fracture. Lumbar spine (L₂–L₄) and total body less head (TBLH) Z-scores were calculated using different size adjustment techniques, namely BMD_a and volumetric BMD for age (bone mineral apparent density (BMAD)); bone mineral content (BMC) and bone area for height; BMC for bone area; BMC for lean mass (adjusted for height); and BMC for bone and body size.

Results

Unadjusted L₂–L₄ and TBLH BMD_a were most sensitive but least specific at distinguishing children with fracture. All size adjustments reduced sensitivity but increased post-test probabilities, from a pre-test probability of 40 % to between 58 and 77 %. The greatest odds ratio for fracture was L₂–L₄ BMAD for a vertebral fracture and TBLH for lean body mass (LBM) (adjusted for height) for a long bone fracture with diagnostic odds ratios of 9.3 (5.8–14.9) and 6.5 (4.1–10.2), respectively.

Conclusion

All size adjustment techniques improved the predictive ability of DXA. The most accurate method for assessing vertebral fracture was BMAD for age. The most accurate method for assessing long bone fracture was TBLH for LBM adjusted for height.     

Bone geometry, density, and strength indices of the distal radius reflect loading via childhood gymnastic activity.

The distal radius bears unique forces during gymnastic activity. Its relatively simple anatomy, minimal soft tissue envelope, and varied composition make the distal radius ideal for evaluating the effects of loading on bone properties. For 56 premenarcheal gymnasts and nongymnasts, ultradistal and 1/3 distal radius DXA scans measured bone mineral content (BMC), areal bone mineral density, and projected area. Simplified geometric models were used to generate bone mineral apparent density (BMAD), geometric indices, strength indices, and fall strength ratios. Ratios of regional BMC vs total body fat-free mass (FFM) were calculated. Separate Tanner I and II analyses of covariance adjusted bone parameters for age and height. Ratios were compared using maturity-matched analyses of variance. At the 1/3 region, periosteal width, BMC, cortical cross-sectional area, and section modulus were greater in gymnasts than nongymnasts (p<0.05); 1/3 BMAD means were equivalent. Ultradistal BMAD, BMC, and index for structural strength in axial compression were higher in gymnasts than nongymnasts; ultradistal periosteal width was only larger in Tanner I gymnasts. Fall strength ratios and BMC/FFM ratios were greater in gymnasts (p<0.05). Geometric and volumetric responses to mechanical loading are site specific during late childhood and early adolescence.     

Age trends of bone mineral density and percentile curves in healthy Chinese children and adolescents

The clinical utility of dual-energy X-ray absorptiometry (DXA) measurement requires appropriate normative values, designed to be diverse with respect to age, gender and ethnic background. The purpose of this study was to generate age-related trends for bone density in Chinese children and adolescents, and to establish a gender-specific reference database. A total of 1,541 Chinese children and adolescents aged from 5 to 19-years were recruited from southern China. Bone mineral density (BMD), bone mineral content (BMC), and bone area (BA) were measured for the total body (TB) and total body less head (TBLH). The height-for-age, height-for-BA, and BMC-for-BA percentile curves were developed using the least mean square method. TB BMD and TBLH BMD were highly correlated. After 18 years, TB BMD was significantly higher in boys than girls. For TB BMC and TBLH BMC, gender differences were found in age groups 12 years and 16–19 years; however, the TBLH BMD was significantly different between genders >16 years. The head region accounted for 13–52 and 16–49 % of the TB BMC in boys and girls, respectively. Furthermore, the percentages were negatively correlated with age and height. This study describes a gender-specific reference database for Chinese children and adolescents aged 5–19 years. These normative values could be used for clinical assessment in this population.     

Pubertal bone growth in the femoral neck is predominantly characterized by increased bone size and not by increased bone density—a 4-year longitudinal study

Fragility fractures are correlated to reduced bone size and/or reduced volumetric bone density (vBMD). These region-specific deficits may originate from reduced mineral accrual and/or reduced skeletal growth during the first 2 decades of life. Before pathological development can be defined, normal skeletal growth must be described. To evaluate growth of bone size, accrual of bone mineral content (BMC), areal bone mineral density (aBMD) and vBMD in a population-based cohort, 44 boys and 42 girls were followed by annual measurements from the age of 12 to 16 (attendance rates 90-100%). Segmental bone length, bone width, BMC, aBMD and vBMD were measured by dual-energy X-ray absorptiometry (DXA). Data were compared with predicted adult peak, as determined in 36 men aged 27.7+/-4.6 years and 44 women aged 26.8+/-4.9 years. Growth in width of the femoral neck precedes accrual of BMC in the femoral neck in both genders up to age 15. The girls were at all ages closer to their predicted adult peak in both bone width and BMC compared with the boys except in the femoral neck. As femoral neck vBMD had reached its predicted adult peak already at 12 years in both genders, the increase in femoral neck BMC and femoral neck aBMD from age 12 to 16 was most likely to be explained by the increase in bone size. In boys the peak velocity growth was recorded at ~14 years for BMC, height, width and lean mass. Growth from the age of 12 to 16 seems to build a bigger but not a denser skeleton in the femoral neck.     

Bone mineral density by age, gender, pubertal stages, and socioeconomic status in healthy Lebanese children and adolescents

Gender, ethnicity, and lifestyle factors affect bone mass acquisition during childhood, thus the need for age- and sex-adjusted Z scores using ethnic-specific data for bone mineral density (BMD) measurement. This study aimed at establishing normative data for BMD in healthy Lebanese children and adolescents. Three hundred sixty-three healthy children aged 10 to 17 years (mean+/-SD: 13.1+/-2.0) were studied. BMD, bone mineral content (BMC), and lean mass were measured by dual-energy X-ray absorptiometry (DXA) using a Hologic 4500A device, and apparent volumetric BMD (BMAD) of the lumbar spine and the femoral neck were calculated. BMD, BMC, and BMAD were expressed by age groups and Tanner stages for boys and girls separately. There was a significant effect of age and puberty on all bone parameters, except at the femoral neck BMAD in boys. BMC and BMD were higher at cortical sites in boys, including subtotal body and hip; whereas, in girls, it was higher at a site more enriched in trabecular bone, namely the lumbar spine. At several skeletal sites, girls had significantly higher BMD adjusted for lean mass than boys. By the end of puberty, adolescents had a mean BMD that was 43-66% higher at the lumbar spine and 25-41% higher at cortical sites than pre-pubertal children, depending on the gender. Mean BMD values in the study group were significantly lower (P<0.01) than Western normative values, with Z scores ranging between -0.2 and -1.1. In both genders, children of lower socioeconomic status tended to have lower BMD than those from a higher socioeconomic background. This study allows additional insight into gender dimorphism in mineral accretion during puberty. It also provides a valuable reference database for the assessment of BMD in children with pubertal or growth disorders who are of Middle Eastern origin.     

Normative data and percentile curves for Dual Energy X-ray Absorptiometry in healthy Indian girls and boys aged 5-17 years

For the correct interpretation of Dual Energy X-ray Absorptiometry (DXA) measurements in children, the use of age, gender, height, weight and ethnicity specific reference data is crucially important. In the absence of such a database for Indian children, the present study aimed to provide gender and age specific data on bone parameters and reference percentile curves for the assessment of bone status in 5-17 year old Indian boys and girls. A cross sectional study was conducted from May 2006 to July 2010 on 920 (480 boys) apparently healthy children from schools and colleges in Pune City, India. The GE-Lunar DPX Pro Pencil Beam DXA scanner was used to measure bone mineral content (BMC [g]), bone area (BA [cm(2)]) and bone mineral density (BMD [g/cm(2)]) at total body, lumbar spine and left femur. Reference percentile curves by age were derived separately for boys and girls for the total body BMC (TBBMC), total body BA (TBBA), lumbar spine bone mineral apparent density (BMAD [g/cm(3)]), and left femoral neck BMAD. We have also presented percentile curves for TBBA for height, TBBMC for TBBA, LBM for height and TBBMC for LBM for normalizing bone data for Indian children. Mean TBBMC, TBBA and TBBMD were expressed by age groups and Tanner stages for boys and girls separately. The average increase in TBBMC and TBBA with age was of the order of 8 to 12% at each age group. After 16 years of age, TBBMC and TBBA were significantly higher in boys than in girls (p<0.01). Maximal increase in TBBMD occurred around the age of 13 years in girls and three years later in boys. Reference data provided may be used for the clinical assessment of bone status of Indian children and adolescents.     

Fat mass increase in 7-year-old children: More Bone Area but lower Bone Mineral density

The main aims of this study were, to evaluate what effect a change in fat mass (FM) and lean body mass (LBM) has on bone parameters over 2 years’ time, in 7-year-old school children and to see what effect fitness had on bone parameters in these children. A repeated-measures design study was conducted where children born in 1999 from six elementary schools in Reykjavik, Iceland were measured twice. All children attending second grade in these six schools were invited to participate. Three hundred twenty-one children were invited, 211 underwent dual-energy X-ray absorptiometry (DXA) scans at the age of seven, and 164 (78 %) of the 211 had DXA scans again 2 years later. Increase in both FM and LBM was associated with increased total body bone mineral content (BMC) and bone area (BA). An increase in FM was more strongly positively associated with BA while an increase in LBM was more strongly associated with an increase in BMC. An increase in FM was negatively associated with change in bone mineral density (BMD), but an increase in LBM was positively associated with change in BMD. Fitness was positively associated with bone parameters when weight, height and sex were accounted for. The present results suggest that an increase in fat mass over 2 years is associated with an increase in BA and BMC, but a decrease in BMD in the whole body. An increase in LBM accrual, on the other hand, is positively associated with all bone parameters in the body. Fitness is associated with both BMC and BMD but not BA.     

Correlation between hand and total body bone density in normal Chinese children

Hand bone mineral density (BMD) in adults was found to be significantly correlated with various skeletal sites, including the total body. However, the relationships between hand and total body bone measurements have yet to be explored for children. We conducted a cross-sectional study of 892 normal Chinese children (511 males, 381 females) aged 5-14 years by measuring the BMD and bone mineral content (BMC) at the total hand, upper limb, subtotal body, and total body using dual-energy X-ray absorptiometry (DXA). We found that hand BMD and BMC increased with age for both genders. Female children had significantly higher hand BMD and BMC than males. Age explained more variance in hand BMD for females (R2=0.727) than for males (R2=0.596). For both genders, hand BMD and BMC correlated highly with age, weight, height, total body lean mass, and BMD and BMC at the upper limb, subtotal body, and total body (r=0.730-0.965, p<0.001) and moderately with body mass index and total body fat mass (r=0.525-0.701, p<0.001). Therefore, the hand DXA scan can potentially be a new tool for the clinical assessment of bone health in children.     

Changes in trabecular bone score and bone density in female adolescents with anorexia nervosa: a longitudinal study

Impaired bone health is a common complication of anorexia nervosa (AN). We aimed to assess longitudinal changes in bone mineral density (BMD) and trabecular bone score (TBS), a measure of bone quality, in female adolescents with anorexia nervosa (AN). We conducted a retrospective longitudinal study of 41 female adolescents with AN who underwent two dual-energy X-ray absorptiometry (DXA) scans. Clinical data, including age, weight, height, body mass index (BMI), and DXA measurements were retrieved from the medical charts. Lumbar bone mineral apparent density (BMAD) was calculated to correct for size. Changes (Δ) in BMD, BMAD, and TBS were examined for correlations with clinical characteristics. Mean ages at the time of DXA scans were 14.8±1.9 and 16.8±2.0 years. There was a significant improvement in anthropometric parameters and DXA measurements at the second DXA scan. However, these values were still significantly lower than expected in the general population. The Δlumbar BMD Z-score was 0.3±0.7, the Δlumbar BMAD Z-score was 0.2±0.7 and the ΔTBS Z-score was 0.5±0.7. ΔTBS Z-score was positively correlated with Δheight Z-score, Δweight Z-score and ΔBMI Z-scores, and negatively correlated height Z-score, weight Z-score and TBS Z-scores at the first DXA scan (p<0.05). Δheight Z-score, ΔBMI Z-score and the progression from early to late puberty were identified as significant independent predictors of Δlumbar BMAD Z-score (p<0.05). During two years of treatment, both BMD and TBS increased significantly. Improvement in height and in weight status, and progression in puberty are predictors of improvement in BMD and TBS.     

Bone Assessment in Children: Comparison of Fan-Beam DXA Analysis

The newest version of whole body dual-energy X-ray absorptiometry (DXA) analysis software from Hologic (Discovery 12.1) is designed to enhance bone detection in smaller subjects. We re-analyzed 1127 pediatric scans (ages 1.8-18.5 yr) previously analyzed using software version 11.2. Regression analysis compared new and original results for bone area (BA), bone mineral content (BMC), bone mineral density (BMD), and DXA-derived body weight. Changes in total and regional bone results were compared with age, weight, and height. New results were highly correlated with original analyses (R2 > or = 0.9), but there were large differences at the individual subject level. The BA and BMC values increased in subjects less than 40 kg weight, resulting in a lower BMD. Original and new results were equivalent by about age 14 yr in both genders. Regional bone data showed the greatest changes in the legs. The newest software produces significant changes in bone values in subjects weighing less than 40 kg, compared with earlier versions. This effect increases with decreasing body weight. This will impact interpretation of longitudinal pediatric DXA studies, as well as existing pediatric whole body bone reference databases. Investigators must recognize which DXAsoftware version they are using, and which version produced any reference database they may use for comparison.     

Bone mineral density in prepubertal obese and control children: relation to body weight,lean mass,and fat mass

The aim of the study was to determine the influence of obesity on bone status in prepubertal children. This study included 20 obese prepubertal children (10.7 +/- 1.2 years old) and 23 maturation-matched controls (10.9 +/- 1.1 years old). Bone mineral area, bone mineral content (BMC), bone mineral density (BMD), and calculation of bone mineral apparent density (BMAD) at the whole body and lumbar spine (L1-L4) and body composition (lean mass and fat mass) were assessed by DXA. Broadband ultrasound attenuation (BUA) and speed of sound (SOS) at the calcaneus were measured with a BUA imaging device. Expressed as crude values, DXA measurements of BMD at all bone sites and BUA (69.30 versus 59.63 dB/MHz, P < 0.01) were higher in obese children. After adjustment for body weight and lean mass, obese children displayed lower values of whole-body BMD (0.88 versus 0.96 g/cm2, P < 0.05) and BMC (1190.98 versus 1510.24 g, P < 0.01) in comparison to controls. When results were adjusted for fat mass, there was no statistical difference between obese and control children for DXA and ultrasound results. Moreover, whole-body BMAD was lower (0.086 versus 0.099 g/cm3, P < 0.0001), whereas lumbar spine BMAD was greater (0.117 versus 0.100 g/cm3, P < 0.001) in obese children. Thus, it was observed that, in obese children, cortical and trabecular bone displayed different adaptation patterns to their higher body weight. Cortical bone seems to enhance both size and BMC and trabecular bone to enhance BMC. Finally, considering total body weight and lean mass of obese children, these skeletal responses were not sufficient to compensate for the excess load on the whole body.     

Bone densitometry: which skeletal sites are best predicted by bone mass determinants?

Evaluation of bone mineral content/bone mass density (BMC/BMD) is important to determine bone mass development among adolescents in health and disease. It is uncertain at which skeletal site BMC/BMD is best predicted by bone mass determinants. On the other hand, intrapersonal BMC/BMD data can be clustered into a composite index score to facilitate correlation and outcome prediction analysis. This study aimed to identify the skeletal site that was best predicted by bone mass determinants and to develop a composite index score based on multisite BMC/BMD values in healthy adolescent girls. Eleven BMD/BMC variables per subject were evaluated by using dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) in 236 healthy girls aged 12–15 years. Bone mass determinants, namely, weight, height, puberty, dietary calcium, physical activity, and bone turnover markers, were determined. Factor analysis was used to develop composite index scores that summarized characteristics of multisite BMC/BMD. Results showed that lumbar spinal BMD and BMC (by DXA) and tibial integral BMD (by pQCT) were the BMC/BMD sites better predicted by bone mass determinants (R ², 0.57–0.77) in multiple regression analysis. On the other hand, three composite index scores representing areal BMD, areal BMC, and vBMD were derived to summarize the original BMC/BMD values. The composite index scores had similar predicting power (R ², 0.419–0.749) compared to those of original BMC/BMD, indicating that the composite index scores were representative of the original variables. To conclude, lumbar spinal BMD and BMC and tibial integral BMD were the three BMC/BMD variables better predicted by bone mass determinants. This evaluation would help select appropriate skeletal sites as outcome measures for bone mass evaluation in future studies. Also, the development of composite index scores could help reduce the number of variables for correlation and outcome prediction analyses.