Sex differences in trabecular bone microarchitecture are not detected in pre and early pubertal children using magnetic resonance imaging

Abstract

Introduction: Sex differences in trabecular bone microarchitecture have been reported in adults and adolescents, but studies in children are lacking. The primary aim of this study was to determine if there are sex differences in magnetic resonance imaging (MRI)-based measures of trabecular bone microarchitecture at the distal femur of children.

Materials and methods: Pre and early pubertal boys (n=23) and girls (n=20) between the 5th and 95th percentiles for height, body mass and BMI were studied. Apparent trabecular bone volume to total volume (appBV/TV), trabecular number (appTb.N), trabecular thickness (appTb.Th), trabecular separation (appTb.Sp) and a composite measure of trabecular bone microarchitecture (TBMcom) were assessed at the lateral aspect of the distal femur using MRI. Areal bone mineral density (aBMD), bone mineral content (BMC) and bone area were assessed at the distal femur using dual-energy X-ray absorptiometry (DXA). Tanner staging was used to assess pubertal development. Physical activity was assessed using an accelerometry-based activity monitor. Calcium intake was assessed using diet records.

Results: There were no sex differences in age, height, femur length, body mass, physical activity or calcium intake (all P>0.05). There were no sex differences in any MRI-based measure of trabecular bone microarchitecture. Consistent with the MRI-based measures, there were no differences in aBMD, BMC or bone area from DXA at the distal femur (P>0.05). appBV/TV, appTb.N, appTb.Th, appTb.Sp and TBMcom were also moderately to strongly related to aBMD (r=0.73, 0.63, 0.51, -0.74 and 0.61, respectively, p<0.001) and BMC (r=0.84, 0.63, 0.66, -0.80 and 0.77, respectively, P<0.001).

Conclusions: The findings suggest that there are no differences in measures of trabecular bone microarchitecture at the distal femur of pre and early pubertal boys and girls who are similar in size, physical activity and calcium intake. Future studies with larger sample sizes that cover all pubertal stages are needed to determine if sex differences in trabecular bone microarchitecture emerge at the distal femur and other weight bearing bone sites.

Figure 1

A visual description of the procedure used to determine measures of apparent trabecular bone microarchitecture in the lateral aspect of the distal using magnetic resonance images is depicted. Twenty six images were collected immediately above the growth plate in the distal femur at demonstrated by a coronal image of the distal femur (A). The 20 most central raw images (B) were filtered using a low-pass filter-based correction algorithm and then reversed in gray scale to facilitate visualization (C). The lateral half of the bone was manually identified by first separating the medial and lateral aspects of the distal femur beginning at the trochlear groove (large arrow) and extending perpendicular to the posterior portion of the bone (medium arrow) and then separating the trabecular bone from the cortical shell (small arrows). Eight samples were taken from the cortical shell in each image (D). The three cortical bone samples with the highest signal intensity were then used to separate the region of interest into bone and marrow phases (binarized; E). Measures of trabecular bone microarchitecture were calculated for each of the twenty binarized images, as described by Majumdar et al. [7], and the averages are reported.

Figure 2

A comparison of trabecular bone microarchitecture measures from MRI in the distal femur of 6 to 12 year-old boys and girls. Values are means ± SD.

Figure 3

A comparison of a composite measure of trabecular bone microarchitecture from MRI (TBMcom) presented as a Z-score and areal bone mineral density (aBMD), bone mineral content (BMC) and bone area from DXA in the distal femur of 6 to 12 year-old boys and girls. Values are means ± SD.

Figure 4

Scatter plot of aBMD from DXA vs. appBV/TV from MRI at the distal femur (r² = 0.527, p < 0.001). The solid line represents the regression line for the combined sample of boys and girls.