Association between bone mass and fractures in children: a prospective cohort study

Abstract

This is the first prospective cohort study of the association between bone mass and fracture risk in childhood. A total of 6213 children 9.9 years of age were followed for 24 months. Results showed an 89% increased risk of fracture per SD decrease in size-adjusted BMC.

Introduction: Although previous case-control studies have reported that fracture risk in childhood is inversely related to bone mass, this has not been confirmed in prospective studies. Additionally, it remains unclear which constituent(s) of bone mass underlie this association. We carried out a prospective cohort study to examine the relationship between DXA measures in children 9.9 years of age and risk of fracture over the following 2 years.

Materials and methods: Total body DXA scan results obtained at 9.9 years of age were linked to reported fractures over the following 2 years in children from a large birth cohort in southwest England. DXA measures consisted of total body less head (TBLH) BMD, bone area, and BMC, and results of subregional analysis of the humerus. Analyses were adjusted for age, sex, ethnicity, and social position.

Results: Complete data were available on 6213 children. There was a weak inverse relationship between BMD at 9.9 years and subsequent fracture risk (OR per SD decrease = 1.12; 95% CI, 1.02-1.25). In analyses examining the relationship between fracture risk and volumetric BMD, fracture risk was inversely related to BMC adjusted for bone area, height, and weight (OR = 1.89; 95% CI, 1.18-3.04) and to estimated volumetric BMD of the humerus (OR = 1.29; 95% CI, 1.14-1.45). Fracture risk was unrelated to both TBLH and humeral bone area. However, in analyses of the relationship between fracture risk and bone size relative to body size, an inverse association was observed between fracture risk and TBLH area adjusted for height and weight (OR = 1.51; 95% CI, 1.17-1.95).

Conclusions: Fracture risk in childhood is related to volumetric BMD, reflecting an influence of determinants of volumetric BMD such as cortical thickness on skeletal fragility. Although bone size per se was not related to fracture risk, we found that children who fracture tend to have a smaller skeleton relative to their overall body size.

FIG. 1

Relationship between tertile of (A) TBLH BMC or (B) TBLH BA as measured at age 9.9 years and the risk of fracture over the following 2 years. TBLH BMC is adjusted for (i) age, sex, ethnicity, maternal education, and paternal social class, and (ii) additionally adjusted for height, log-transformed weight and TBLH BA. TBLH BA is adjusted for (i) age, gender, ethnicity, maternal education and paternal social class and (ii) additionally adjusted for height and log-transformed weight. Graphs show mean ORs ± 95% CIs for the association between each tertile and fracture risk (1 = lowest tertile, 3 = highest), calculated by logistic regression. The highest tertile was taken as the baseline category, and the p values are for the test for trend. TBLH BMC and TBLH BA were reduced to categorical variables (tertiles) after adjustment. The dotted line represents the null value of 1.

FIG. 2

Relationship between tertile of humeral vBMD as measured at 9.9 years of age and the risk of fracture risk over the following 2 years, adjusted for age, sex, ethnicity, maternal education, paternal social class, height, and log-transformed weight. Graphs show mean ORs ± 95% CIs for the association between each tertile and fracture risk (1 = lowest tertile, 3 = highest), calculated by logistic regression. The highest tertile was taken as the baseline category, and the p values are for the test for trend. Humeral vBMD was reduced to a categorical variable (tertiles) after adjustment. The dotted line represents the null value of 1.