Regional variations of gender-specific and age-related differences in trabecular bone structure of the distal radius and tibia

Abstract

Regional variation in trabecular structure across axial sections is often obscured by the conventional global analysis, which takes an average value for the entire trabecular compartment. The objective of this study is to characterize spatial variability in trabecular structure within a cross-section at the distal radius and tibia, and gender and age effects using in vivo high-resolution peripheral quantitative computed tomography (HR-pQCT). HR-pQCT images of the distal radius and tibia were acquired from 146 healthy individuals aged 20-78 years. Trabecular bone volume fraction (BV/TV), number (Tb.N), thickness (Tb.Th), separation (Tb.Sp), and heterogeneity (Tb.1/N.SD) were obtained in a total of 11 regions-the entire trabecular compartment (the global means), inner, outer, and eight defined subregions. Regional variations were examined with respect to the global means, and compared between women and men, and between young (20-29 years old) and elderly (65-79 years old) adults. Substantial regional variations in trabecular bone structure at the distal radius and tibia were revealed (e.g. BV/TV varied -40% to +57% and -59% to +100% of the global means, respectively, for elderly women). The inner-lateral (IL) subregion had low BV/TV, Tb.N, and Tb.Th, and low Tb.Sp and Tb.1/N.SD at both sites; the opposite was true in the outer-anterior (OA) subregion at the distal radius and the outer-medial (OM) and -posterior (OP) subregions at the distal tibia. Gender differences were most pronounced in the inner-anterior (IA) subregion compared to the other regions or the global mean differences at both sites. Trabecular structure associated with age and differed between young and elderly adults predominantly in the inner-posterior (IP) subregion at the distal radius and in the IL and IA subregions at the distal tibia; on the other hand, it remained unchanged in the OA subregion at the distal radius and in the OM subregion at the distal tibia for both women and men. This study demonstrated that not only the conventional global analysis can obscure regional differences, but also assuming bone status from that of smaller subregion may introduce a confounding sampling error. Therefore, a combined approach of investigating the entire region, each subregion, and the cortical compartment may offer more complete information.

Figure 1

Representative HR-pQCT images of cross-sections of human distal left radius (top) and tibiae (bottom) with low Tb.1/N.SD (more homogenously distributed) (left) and high Tb.1/N.SD (more heterogeneous distributed) (right). Notice that not only the distribution but also the thickness of trabeculae varies from subregion to subregion.

Figure 2

The region definitions at the distal radius (left) and tibia (right) used in this study. A total of 8 subregions were defined at each slice as follows. The trabecular compartment was divided into two concentric circular regions (inner and outer subregions) where the area of inner subregion was 60% of the entire trabecular region. The trabecular compartment was further divided into angular quadrants based on the defined reference line (dashed). The major axis of the cross-section was used as a reference for radius, and the quadrants were placed 45° to it. The line connecting the centroids of the tibia and fibula cross-sections was used as a reference for tibia, and quadrants were placed 0° to it.

Figure 3

The mean percent difference from the global means in each subregion for each structure index for elderly women at the distal radius (top) and tibia (bottom). Similar patterns were observed for elderly men and young adults. Significant difference from the global mean with ^a p < 0.005; ^b p < 0.001 determined by multivariate RMANOVA and post-hoc contrast test.

Figure 4

The mean percent difference in the trabecular structure indices for elderly women (N = 13) compared to elderly men (N = 9) in each subregion at the distal radius (top) and tibia (bottom). Significant difference from elderly men with ^a p < 0.05; ^b p < 0.01; ^c p < 0.001 using Mann-Whitney U test.

Figure 5

The mean percent difference in the trabecular structure indices for elderly women (N = 13) compared to young women (N = 17) in each subregion at the distal radius (top) and tibia (bottom). Significant difference from young women with ^a p < 0.05; ^b p < 0.01; ^c p < 0.001 using Mann-Whitney U test.