Effects of sex and age on bone microstructure at the ultradistal radius: a population-based noninvasive in vivo assessment

Abstract

In a population-based cross-sectional study, we examined effects of sex and age on bone microstructure at the wrist using high-resolution 3-D pQCT. Compared with women, men had thicker trabeculae in young adulthood and had less microstructural damage with aging. These findings may contribute to the virtual immunity of men to age-related increases in wrist fractures.

Introduction: Although changes in bone microstructure contribute to fracture risk independently of BMD, it has not heretofore been possible to assess this noninvasively in population-based studies.

Materials and methods: We used high-resolution 3-D pQCT imaging (voxel size, 89 mum) to define, in a random sample of women (n = 324) and men (n = 278) 21-97 years of age, sex and age effects on bone microstructure at the wrist.

Results: Relative to young women (age, 20-29 years), young men had greater trabecular bone volume/tissue volume (BV/TV; by 26%, p = 0.001) and trabecular thickness (TbTh; by 28%, p < 0.001) but similar values for trabecular number (TbN) and trabecular separation (TbSp). Between ages 20 and 90 years, cross-sectional decreases in BV/TV were similar in women (-27%) and in men (-26%), but whereas women had significant decreases in TbN (-13%) and increases in TbSp (+24%), these parameters had little net change over life in men (+7% and -2% for TbN and TbSp, respectively; p < 0.001 versus women). However, TbTh decreased to a greater extent in men (-24%) than in women (-18%; p = 0.010 versus men).

Conclusions: Whereas decreases with age in trabecular BV/TV are similar in men and women, the structural basis for the decrease in trabecular volume is quite different between the sexes. Thus, over life, women undergo loss of trabeculae with an increase in TbSp, whereas men begin young adult life with thicker trabeculae and primarily sustain trabecular thinning with no net change in TbN or TbSp. Because decreases in TbN have been shown to have a much greater impact on bone strength compared with decreases in TbTh, these findings may help explain the lower life-long risk of fractures in men, and specifically, their virtual immunity to age-related increases in distal forearm fractures.

FIG. 1

(A) Radiograph showing the site of imaging at the distal radius. The white line indicates the beginning of the joint space and the red lines indicate the section of bone over which images are acquired. (B) Representative cross-sectional images from the stack of CT slices from proximal (top left) to distal (bottom right). (C) Representative 3-D image.

FIG. 2

Age-related changes in trabecular bone microstructural variables at the wrist in Rochester, MN, women and men. (A) Bone volume/tissue volume (BV/TV). (B) Trabecular number (TbN). (C) Trabecular thickness (TbTh). (D) Trabecular separation (TbSp). Curve fitting was done with a smoother function. Individual values and smoother lines are given for women using open circles and dashed lines and for men using closed circles and solid lines.

FIG. 3

Representative 3-D reconstructions of images from young, middle-aged, and elderly men (left) and women (right). Also indicated are the values for trabecular microstructural variables in each of these subjects. The arrow at the top left indicates prominence of apparent plate-like trabeculae in the young man, which are absent or considerably less prominent in the other images.