The Association between Bone Mineral Density, Metacarpal Morphometry, and Upper Limb Fractures in Children: A Population-Based Case-Control Study

0013-7227/03/$15.00/0 Printed in U.S.A. The Journal of Clinical Endocrinology & Metabolism 88(4):1486 –1491 Copyright © 2003 by The Endocrine Society doi: 10.1210/jc.2002-021682 The Association between Bone Mineral Density, Metacarpal Morphometry, and Upper Limb Fractures in Children: A Population-Based Case-Control Study DEQIONG MA AND GRAEME JONES Menzies Research Institute, Hobart, Tasmania 7000, Australia F RACTURE INCIDENCE IS bimodal with two age peaks (1). Fractures due to osteoporosis in later life are a well recognized public health problem. There is also another peak in younger life between the ages of 10 and 15, especially for upper limb fractures (2– 6). The causes of these fractures have been much less completely studied than fractures in later life. Bone mass has been inconsistently associated with fractures in children (7–13). The strongest evidence reported a significant association between bone mass and distal forearm fractures in both boys and girls (10, 11). However, all studies have variations with regard to the age group, choice of controls, and fracture type studied. These factors, when combined with generally small sample sizes, are likely to explain some of the inconsistency. Furthermore, other bone strengthrelated factors such as cortical thickness, biomechanics, and microstructure may also be important in fracture etiology in children (12, 14) as has been shown in adults (15, 16). These factors are difficult to assess in children due to concerns about radiation exposure. Metacarpal morphometry is a technique that may lead to further understanding of the role of these factors, but there have been no studies to date. The aim, therefore, of this population-based case-control study was to investigate the association between bone mass assessed by both dual energy x-ray absorptiometry (DXA) and metacarpal morphometry and upper limb fractures in boys and girls 9 –16 yr of age. Abbreviations: aBMD, Areal BMD; AUC, area under the receiver operating characteristic curve; BMAD, bone mineral apparent density; BMC, bone mineral content; BMD, bone mineral density; BMI, body mass index; CI, confidence interval; DXA, dual energy absorptiometry; MI, metacarpal index; OR, odds ratio. 0.05). For metacarpal measures, cases had a thinner cortical width and lower MI for wrist and forearm fractures only. In multivariate modeling, both spine BMAD (odds ratio, 1.4/SD reduction) and MI (odds ratio, 1.5/SD reduction) remained statistically significant predictors of wrist and forearm fractures. In conclusion, both DXA measures and MI are independently associated with wrist and forearm but not other upper limb fractures. The magnitude of this association is somewhat weaker than in adults but suggests that optimizing ageappropriate bone mass will lessen the risk of fracture in children. (J Clin Endocrinol Metab 88: 1486 –1491, 2003) Subjects 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 the study were to investigate the role of growth, bone strength, sports participation, risk taking, and coordination in the etiology of upper limb fractures in children 9 –16 yr old. Subjects and/or their parent/guardian who provided informed consent to take part underwent an extensive protocol involving measurements of anthropometry, pubertal stage, bone density, metacarpal morphometry, bone age, clumsiness, risk taking behavior, physical activity, sunlight exposure, questionnaire assessment by parent/guardian of socio-economic factors, details of fracture, and habitual intake of dairy products. The current study relates to bone density and metacarpal morphometry only. Ethical approval for this study was obtained from the University of Tasmania Ethics Committee (Human Experimentation). Selection of cases and controls From May 1998 to January 2002, subjects aged 9 –16 yr from a preexisting fracture registry (6), who sustained a single-site upper limb fracture, were invited to take part. In brief, the fracture registry received reports containing the word “fracture” from all radiology providers from Southern Tasmania on a monthly basis. This region is larger than and fully encompasses the study area. Potential subjects were then screened from the registry by the authors and invited to take part by a letter of invitation, with a follow-up telephone call for subject and parental consent. Fracture subjects were excluded if they had diseases that would prevent them from completing the full protocol, such as cerebral palsy and arthrogryposis; if they had moved out of the study area; if they were not enrolled in school; or if they had a previous upper limb fracture between the ages 9 and 16 yr. Nonresponders who were more than 3 months past the date of fracture were also excluded. Controls were randomly selected from the same school class as the cases in the ratio of one control for every case (using available school lists and random numbers). They were also individually matched with cases by gender. Potential controls that had experienced an upper limb fracture between the ages of 9 and 16 yr were excluded. 1486 The aim of this population-based case-control study was to examine the association between bone mass and upper limb fractures in children aged 9 –16 yr. Areal bone mineral density and bone mineral apparent density (BMAD) were measured by both dual energy absorptiometry (DXA) and metacarpal index (MI) by hand radiograph. A total of 321 fracture cases and 321 randomly selected individually matched controls were studied. For all fractures, cases had lower DXA measures at all sites (1.1–3.3%; all P < 0.05). A larger reduction was observed for those with wrist and forearm fractures (1.2– 4.5%; all P < 0.05, except total body BMAD) but not other upper limb fractures (hand, ⴚ1.6 to ⴙ1.2%; upper arm: 0.9 – 4.8%; all P > Ma and Jones • Bone Mass in Children with Upper Limb Fractures Anthropometry measurements and Tanner stage assessment Weight was measured with light indoor clothing without shoes to the nearest 0.1 kg using electronic scales (calibrated at the beginning of the study by the manufacturer). Height was measured without shoes to the nearest 0.1 cm on a stadiometer. Tanner stage was assessed by a validated self-administered instrument using drawings made from Tanner’s photographs, which illustrate the five stages of genital development for boys and breast development for girls (17). Bone density measurements Metacarpal morphometry Measurements were made from postero-anterior left hand radiographs taken at a uniform 1-m tube-to-film distance. Morphometric measurements are performed at the midshaft of the left second metacarpal by one examiner. The detailed method in defining the inner limit and length of second metacarpal was as previously described (19). Hand radiographs we (...truncated)