Elsevier

Journal of Clinical Densitometry

Volume 9, Issue 2, April–June 2006, Pages 202-209
Journal of Clinical Densitometry

Original Article
Bone Density Interpretation and Relevance in Caucasian Children Aged 9–17 Years of Age: Insights From a Population-Based Fracture Study

https://doi.org/10.1016/j.jocd.2006.02.004Get rights and content

Abstract

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.

Introduction

Fractures in both later and younger life are a significant public health problem 1, 2, 3. There has been increasing interest in measuring bone density in children on the grounds that increasing peak bone mass may prevent fractures in later life. Direct evidence to support this is lacking, due to the need for very long-term studies, but shorter term and modeling studies have suggested that peak bone mass does make a substantial contribution to fracture risk in later life 4, 5, 6, 7. Furthermore, the lack of other clinical correlates has created much controversy about the interpretation of bone density in children. The effect of bone size on dual-energy X-ray absorptiometry (DXA)-derived values makes this more difficult as it is uncertain whether it is the size of the bone or the amount of bone within the bone envelope that is important. It is clear that the T-score concept applied in adults for the definition of osteoporosis cannot be applied to children as they have not yet reached peak bone mass and virtually all will be classified as osteoporosis due to their smaller body size. The Z-score concept can be applied to children, but it is uncertain as to its validity and what constitutes a low Z-score of clinical significance. A number of different measures have been proposed on theoretical grounds 8, 9, 10 but have not been tested against a clinical marker. More recently, there have been a number of reports, including those from our group, suggesting that forearm and wrist fractures in children are associated with bone density in children 11, 12, 13. To date, other fractures have been inconsistently associated with bone density 14, 15, 16, 17, suggesting that they cannot be used as a clinical marker, although it remains uncertain whether forearm fracture can be used as a clinical marker in children.

Therefore, the questions asked by this study were twofold: (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?

Section snippets

Materials and Methods

This study was conducted from 1998 to 2002 in Hobart, Tasmania, and included the Southern Tasmania metropolitan council areas of Hobart, Clarence, Glenorchy, and Kingborough. Caucasians are predominant in this population. The aims of this study were to investigate the role of growth, bone strength, sports participation, risk-taking behavior, and coordination in the etiology of upper limb fractures in children aged 9–16 yr. Subjects and/or their parent/guardian, who provided informed consent to

Results

A total of 642 subjects took part (boys: n = 215 pairs; girls: n = 106 pairs) representing an overall response rate of 56% (642 of 1,148) of those eligible in the source population during the study period. Table 1 gives basic descriptive data. Although the mean of the BMAD variables was similar to two decimal places, the standard deviation was very small and the differences were statistically significant. Tanner stage distribution was as follows: stage 1: 24%; stage 2: 21%; stage 3: 22%; stage 4:

Discussion

This population based case-control study provides a number of unique insights into the relevance and interpretation of DXA in children. Spine BMAD was the most consistent fracture predictor in both genders. The strong association between all DXA variables and age indicates the need for age-specific reference ranges to calculate Z-scores, whereas 5-yr wrist and forearm fracture risk in children has the potential for immediate clinical relevance.

Our previous report and a number of others have

Acknowledgments

Special thanks to research assistants Fiona Wilson, Anitra Wilson, Lesley Oliver, Val Walsh, as well as the staff of the Medical Imaging Department at Royal Hobart Hospital. This work was supported by the National Health and Medical Research Council of Australia and Clifford Craig Research Trust.

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