The ontogeny of human fetal trabecular bone architecture occurs in a limb-specific manner

Abstract

Gestational growth and development of bone is an understudied process compared to soft tissues and has implications for lifelong health. This study investigated growth and development of human fetal limb bone trabecular architecture using 3D digital histomorphometry of microcomputed tomography data from the femora and humeri of 35 skeletons (17 female and 18 male) with gestational ages between 4 and 9 months. Ontogenetic data revealed: (i) fetal trabecular architecture is similar between sexes; (ii) the proximal femoral metaphysis is physically larger, with thicker trabeculae and greater bone volume fraction relative to the humerus, but other aspects of trabecular architecture are similar between the bones; (iii) between 4 and 9 months gestation there is no apparent sexual or limb dimorphism in patterns of growth, but the size of the humerus and femur diverges early in development. Additionally, both bones exhibit significant increases in mean trabecular thickness (and for the femur alone, bone volume fraction) but minimal trabecular reorganisation (i.e., no significant changes in degree of anisotropy, connectivity density, or fractal dimension). Overall, these data suggest that in contrast to data from the axial skeleton, prenatal growth of long bones in the limbs is characterised by size increase, without major reorganizational changes in trabecular architecture.

Figure 1

Representative spheres sampled from homologous regions of trabecular bone from the proximal metaphyses of fetal humeri and femora, aged 4–9 months gestation. Spheres are 3D volumetric reconstructions of µCT data (isotropic voxel size: 10 µm), shown in orthographic camera projection for comparability of scale. Scale bar = 2 mm.

Figure 2

Mean and standard deviation of fetal trabecular architectural parameters for females (black bars) and males (grey bars). Comparison reveals trabecular architecture of fetal proximal limb bones is similar in both sexes, with no apparent sexual dimorphism. Data were compared by one-way ANOVA with Šídák posthoc tests (only shown for VOI diameter). There were no significant comparisons (ns = p > 0.05).

Figure 3

Mean and standard deviation of fetal trabecular architectural parameters for the humerus (left bar in each pair) and femur (right bar in each pair) in females (black bars), males (light grey bars), and female and male data combined (dark grey bars). Comparison of combined male and female datasets revealed the fetal femur is larger (VOI diameter), with increased bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) than the fetal humerus and exhibited slightly lower DA. Data were compared by one-way ANOVA with Šídák posthoc tests. P values shown for significant results from one-way ANOVA. Asterisks indicate significant differences in posthoc testing: p < 0.05 (*) and p < 0.01 (**).

Figure 4

Mean and standard deviation of fetal trabecular architectural parameters at different fetal ages for humerus (filled circles) and femur (empty circles). Male and female data have been pooled. Comparison of mean morphometric values at 5–9 months relative to 4 months reveals significant increases in the size of the femur and humerus (VOI diameter), trabecular thickness, and BV/TV (femur only) during gestation. However, little reorganisation of trabecular structure is observed in either bone. Data were compared by one-way ANOVA with Šídák posthoc tests. P values shown for significant results from one-way ANOVA (unboxed = femur, boxed = humerus). Details of P values from Šídák posthoc tests can be found in Table S5.