Assessing bone mass in children and adolescents

Diagnosis of osteoporotic vertebral fractures in children

Osteoporosis is a generalised disorder of the skeleton with reduced bone density and abnormal bone architecture. It increases bone fragility and renders the individual susceptible to fractures. Fractures of the vertebrae are common osteoporotic fractures. Vertebral fractures may result in scoliosis or kyphosis and, because they may be clinically silent, it is imperative that vertebral fractures are diagnosed in children accurately and at an early stage, so the necessary medical care can be implemented. Traditionally, diagnosis of osteoporotic vertebral fractures has been from lateral spine radiographs; however, a small number of studies have shown that dual energy x-ray absorptiometry is comparable to radiographs for identifying vertebral fractures in children, while allowing reduced radiation exposure. The diagnosis of vertebral fractures from dual energy x-ray absorptiometry is termed vertebral fracture assessment. Existing scoring systems for vertebral fracture assessment in adults have been assessed for use in children, but there is no standardisation and observer reliability is variable. This literature review suggests the need for a semiautomated tool that (compared to the subjective and semiquantitative methods available) will allow more reliable and precise detection of vertebral fractures in children.

Evaluation of bone mineralization in former preterm born children: Phalangeal quantitative ultrasound cannot replace dual-energy X-ray absorptiometry

Background

Preterm infants are at risk of impaired bone health in later life. Dual-energy X-ray absorptiometry-scan (DXA) is the gold standard to determine bone mineralization. Phalangeal quantitative ultrasound (pQUS) is an alternative technique that is inexpensive, easy to use and radiation-free. The aim of this study was to investigate whether both techniques reveal equivalent results.

Materials and methods

Sixty former preterm infants (31 boys; 29 girls) received a DXA and pQUS at age 9 to 10 years. DXA measured bone mineral content (BMC) and bone mineral density (BMD) for total body and lumbar spine (L1-4), while pQUS measured the amplitude dependent speed of sound (AD-SoS) and bone transit time (BTT) at metacarpals II-IV providing continuous values and Z-scores based on age and sex. Four statistical methods evaluated the association between both techniques: Pearson's correlation coefficients, partial correlation coefficients adjusted for gestational age, height and BMI, Bland-Altman analysis and cross tabulation.

Results

Both techniques showed a statistically significant weak correlation for continuous values as well as Z-scores (0.291–0.462, p < 0.05). Boys had significant and relatively high correlations (0.468–0.585, p < 0.05). In comparison, the correlations for girls were not significant. Correlation coefficients further decreased while calculating the partial correlations. The Bland-Altman plots showed poor agreement. Sensitivity ranged from 33% to 92% and specificity from 16% to 68%. Positive and negative predictive values ranged from 4% to 38% and 82% to 97%, respectively.

Conclusions

We found statistically significant weak correlations and poor agreement between DXA and pQUS measurements. DXA is not equivalent to pQUS and therefore not replaceable by this technique in former preterm born children at the age of 9 to 10 years.

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DXA is the golden standard to determine bone mineralization, while Quantitative ultrasound is a radiation-free alternative.

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Four statistical tests were used to investigate the equivalence of both methods.

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Comparison of results of 60 preterm born children at age 9 to 10 years found poor agreement between both methods.

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There was a discrepancy in differentiating the same children with normal or reduced bone mineralization.

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Quantitative ultrasound cannot replace the DXA scan for determination of bone mineralization in preterm born children.

Estimation of trabecular bone parameters in children from multisequence MRI using texture-based regression

PURPOSE

This paper presents a statistical approach for the prediction of trabecular bone parameters from low-resolution multisequence magnetic resonance imaging (MRI) in children, thus addressing the limitations of high-resolution modalities such as HR-pQCT, including the significant exposure of young patients to radiation and the limited applicability of such modalities to peripheral bones in vivo.

METHODS

A statistical predictive model is constructed from a database of MRI and HR-pQCT datasets, to relate the low-resolution MRI appearance in the cancellous bone to the trabecular parameters extracted from the high-resolution images. The description of the MRI appearance is achieved between subjects by using a collection of feature descriptors, which describe the texture properties inside the cancellous bone, and which are invariant to the geometry and size of the trabecular areas. The predictive model is built by fitting to the training data a nonlinear partial least square regression between the input MRI features and the output trabecular parameters.

RESULTS

Detailed validation based on a sample of 96 datasets shows correlations >0.7 between the trabecular parameters predicted from low-resolution multisequence MRI based on the proposed statistical model and the values extracted from high-resolution HRp-QCT.

CONCLUSIONS

The obtained results indicate the promise of the proposed predictive technique for the estimation of trabecular parameters in children from multisequence MRI, thus reducing the need for high-resolution radiation-based scans for a fragile population that is under development and growth.

Comparison of the relationship between bone marrow adipose tissue and volumetric bone mineral density in children and adults

Several large-scale studies have reported the presence of an inverse relationship between bone mineral density (BMD) and bone marrow adipose tissue (BMAT) in adults. We aim to determine if there is an inverse relationship between pelvic volumetric BMD (vBMD) and pelvic BMAT in children and to compare this relationship in children and adults. Pelvic BMAT and bone volume (BV) was evaluated in 181 healthy children (5-17yr) and 495 healthy adults (≥18yr) with whole-body magnetic resonance imaging (MRI). Pelvic vBMD was calculated using whole-body dual-energy X-ray absorptiometry to measure pelvic bone mineral content and MRI-measured BV. An inverse correlation was found between pelvic BMAT and pelvic vBMD in both children (r=-0.374, p<0.001) and adults (r=-0.650, p<0.001). In regression analysis with pelvic vBMD as the dependent variable and BMAT as the independent variable, being a child or adult neither significantly contribute to the pelvic BMD (p=0.995) nor did its interaction with pelvic BMAT (p=0.415). The inverse relationship observed between pelvic vBMD and pelvic BMAT in children extends previous findings that found the inverse relationship to exist in adults and provides further support for a reciprocal relationship between adipocytes and osteoblasts.

Bone mass and density in preadolescent boys with and without Down syndrome

Preadolescent boys with Down syndrome at 7-10 years of age have lower bone mass and density in the pelvis than age-matched children without Down syndrome. However, bone mass and density of total body less head and lumbar spine are not different between these two groups.

INTRODUCTION

This study aimed to assess bone mineral content (BMC) and density (BMD) in preadolescent boys with and without Down syndrome (DS) at 7-10 years of age.

METHODS

Eleven preadolescent boys with DS and eleven age-matched children without DS participated in this study. Dual-energy X-ray absorptiometry was used to measure BMC and BMD in whole body and lumbar spine. Both BMC and BMD of total body less head (TBLH) and lumbar spine (vertebrae L2-L4) were compared between the two groups, with and without adjusting for physical characteristics such as bone area, body height, and total lean mass. Two bone mineral apparent density (BMAD) variables were calculated to estimate volumetric BMD in the lumbar spine.

RESULTS

Both BMC and BMD in the pelvis were lower in the DS group, after adjusting for physical characteristics. However, with and without adjusting for physical characteristics, the two groups were not different in BMC and BMD of the arms, legs, and TBLH from the whole body scan and in BMC, BMD, and BMAD of the lumbar spine from the lumbar spine scan.

CONCLUSIONS

These findings indicate that the pelvis may be the first site to show the significant difference in BMC and BMD between preadolescent boys with and without DS. It also suggests that significantly lower BMC and BMD in whole body and lumbar spine, which is usually observed in young adults with DS, may not occur before adolescence.

Bone mineral density, hip bone geometry, and calcaneus trabecular bone texture in obese and normal-weight children

Our study aimed at comparing bone mineral density (BMD), geometric indices of hip bone strength, and indices of trabecular bone texture at the calcaneus in obese and normal-weight children. Fifty-three obese children (10.3 ± 1.4 yr) and 24 normal-weight children (10.4 ± 1.5 yr) participated in this study. Body composition, bone mineral content, and BMD at whole body (WB), lumbar spine (L2-L4), total forearm, and proximal femur (total hip [TH] and femoral neck [FN]) were measured by dual-energy X-ray absorptiometry (DXA). Bone geometry of the hip was evaluated by the hip structure analysis (HSA) program. DXA scans were analyzed at the FN at its narrowest region and the femoral shaft (FS) by the HSA program. Cross-sectional area (CSA) and section modulus (Z) were measured from hip BMD profiles. Texture analysis was performed on digitized radiographs of the calcaneus to assess trabecular bone microarchitecture, and the result was expressed as Hmean. WB BMD, L2-L4 BMD, TH BMD, and FN BMD were significantly higher in obese children compared with normal-weight peers (p < 0.05). FN Z and FS Z were not significantly different between the 2 groups, whereas Hmean parameter was significantly lower in obese children compared with normal-weight peers (p < 0.001). After adjustment for body weight, obese children displayed lower WB BMD, FN CSA, FN Z, FS CSA, and FS Z compared with normal-weight children. This study suggests that BMD of WB and geometric indices of hip bone strength are not adapted to the increased body weight in obese children.

Advances in bone imaging for osteoporosis

The diagnosis and management of osteoporosis have been improved by the development of new quantitative methods of skeletal assessment and by the availability of an increasing number of therapeutic options, respectively. A number of imaging methods exist and all have advantages and disadvantages. Dual-energy X-ray absorptiometry (DXA) is the most widely available and commonly utilized method for clinical diagnosis of osteoporosis and will remain so for the foreseeable future. The WHO 10-year fracture risk assessment tool (FRAX(®)) will improve clinical use of DXA and the cost-effectiveness of therapeutic intervention. Improved reporting of radiographic features that suggest osteoporosis and the presence of vertebral fracture, which are powerful predictors of future fractures, could increase the frequency of appropriate DXA referrals. Quantitative CT remains predominantly a research tool, but has advantages over DXA--allowing measurement of volumetric density, separate measures of cortical and trabecular bone density, and evaluation of bone shape and size. High resolution imaging, using both CT and MRI, has been introduced to measure trabecular and cortical bone microstructure. Although these methods provide detailed insights into the effects of disease and therapies on bone, they are technically challenging and not widely available, so they are unlikely to be used in clinical practice.

Anatomically reproducible assessment of volumetric bone mineral density--based on clinical computed tomography

Local distribution and quality of bone mineral density (BMD) in the proximal humerus are important for rotator cuff repair, internal fixations, and arthroplasty. The current study aimed to develop a volumetric BMD (vBMD) measurement technique that can specify the volumetric region of interest in an anatomically reproducible manner and ensures fair comparison of vBMD among intrasubjective or intersubjective measurements. Computed toed into three-dimensional (3D) polygon models. A standardized volumetric block was asmographic images of 10 intact shoulders (from six women and four men, age range 46-69 years) were reconstruct signed, and it included whole insertion areas of the supraspinatus and infraspinatus tendons on the greater tuberosity. For standardizing a bone block, a mathematical method for reproducible landmark assignment and reproducible local coordinate system was developed. After converting the polygonal standardized volumetric block into 3D tetrahedron finite element models, its vBMD was calculated. The repeatability and reproducibility standard deviations of the vBMD measurement method were found to be less than 2%. The current study developed a vBMD measurement technique that can specify the vROI in an anatomically reproducible manner and ensures fair comparison of BMD among intrasubjective or intersubjective measurements, with less than 2% reproducibility error.

Comparative study of dual energy X-ray absorptiometry and quantitative ultrasonography with the use of biochemical markers of bone turnover in boys with haemophilia

Our aim was to evaluate bone status in boys with haemophilia using dual energy X-ray absorptiometry (DXA) and quantitative ultraSonography (QUS), and in addition, to compare these two methods with the use of biochemical markers of bone turnover. Twenty-six boys with a mean decimal age of 12.08 ± 4.44 years were included in the study which included a DXA scan at lumbar spine and radial, as well as tibial QUS. Serum levels of soluble receptor activator of nuclear factor κB ligand (sRANK-L), osteoprotegerin (OPG) and osteocalcin (OC) were measured and joint evaluation was performed using the Hemophilia Joint Health Score (HJHS). With regard to the study results, only 2 of 26 patients (7.7%) had bone mineral density (BMD) Z-scores < -2, and 4 patients (15.4%) had BMD Z-scores between -1 and -2. Only one patient had radial and other two had tibial QUS Z-scores < -2. No agreement was recorded between QUS and DXA in identifying patients at risk for osteoporosis (k = 0.275, P = 0.063). Haemophiliacs had significantly higher serum levels of sRANK-L (21.04 ± 4.78 vs. 18.58 ± 2.28 ng mL(-1), P = 0.038) and of OC (5.35 ± 2.29 vs. 3.09 ± 0.61 ng mL(-1), P = 0.002) and significantly decreased levels of OPG (15.78 ± 2.53 vs. 23.79 ± 4.39 pg mL(-1), P < 0.001) compared with controls. QUS Z-scores at tibia significantly correlated with HJH Scores (r = -0.450, P = 0.040), whereas lumbar BMD Z-scores significantly correlated with body mass index Z-scores (r = 0.500, P = 0.009). More studies are warranted to identify the most accurate densitometric method for assessing bone status in haemophiliacs.

Official positions of the International Society for Clinical Densitometry (ISCD) on DXA evaluation in children and adolescents

Dual-energy X-ray absorptiometry (DXA) is the most widely used technical instrument for evaluating bone mineral content (BMC) and density (BMD) in patients of all ages. However, its use in pediatric patients, during growth and development, poses a much more complex problem in terms of both the technical aspects and the interpretation of the results. For the adults population, there is a well-defined term of reference: the peak value of BMD attained by young healthy subjects at the end of skeletal growth. During childhood and adolescence, the comparison can be made only with healthy subjects of the same age, sex and ethnicity, but the situation is compounded by the wide individual variation in the process of skeletal growth (pubertal development, hormone action, body size and bone size). The International Society for Clinical Densitometry (ISCD) organized a Pediatric Position Development Conference to discuss the specific problems of bone densitometry in growing subjects (9-19 years of age) and to provide essential recommendations for its clinical use.

Evidence-based review of bone strength in children and youth with cerebral palsy

Children with cerebral palsy have various risk factors for compromised bone health. Evidence concerning their bone fragility is gathering; however, there is no consensus regarding risk factors, indications for evaluation, follow-up, or treatment. We performed an evidence-based review targeted to address the following questions concerning children with cerebral palsy: Is bone strength impaired and what are the risk factors? Are these children at increased risk for bone fractures? What are the relations between bone mineral density and fracture risk? What methods can be used for bone health assessment? How can bone strength be improved? Currently, the most acceptable method for evaluating bone status in children is dual-energy x-ray absorptiometry. Evidence demonstrates reduced bone mass in children with cerebral palsy; yet, no clear association with fractures. Preventive methods are suggested.

Osteoporosis in children and adolescents

In recent years, the issue of low bone density in children and adolescents has attracted much attention. The classical definition of osteoporosis should be valid at any age, yet its practical applicability to children and adolescents remains a matter of debate and there is no consensus on a diagnosis based solely on the BMD value. The clinical relevance of uncomplicated low bone density in the young and its long-term consequences remain difficult to evaluate and there is only preliminary evidence that the BMD value is a predictor of fracture risk in growing subjects. Moreover, the interpretation of densitometric data in the young is difficult because the "normal" BMD values to be used for comparison are continuously changing with age, and in addition, depend on several variables, such as gender, body size, pubertal stage, skeletal maturation and ethnicity. Although Z-score values below -2 are generally considered a serious warning, most bone specialists make a diagnosis of osteoporosis in children and adolescents only in the presence of low BMD and at least one fragility fracture. The scope of this review is limited to presenting a picture of the available knowledge. The literature on fractures will be presented in detail, since fractures are one of the key elements in the debate. There are countless papers on fractures in childhood and adolescence, but very few of them attempt to identify fragility fractures, and still fewer develop the concept of osteoporosis in the young in relation to fractures. The different forms of primary and secondary osteoporosis, the more technical aspects of bone densitometry in pediatrics, and the delicate issue of treatment will be discussed only briefly.