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


BACKGROUND
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.


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.
Khosla
Sundeep
S
Endocrine Research Unit, Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA. khosla.sundeep@mayo.edu
Riggs
B Lawrence
BL
Atkinson
Elizabeth J
EJ
Oberg
Ann L
AL
McDaniel
Lisa J
LJ
Holets
Margaret
M
Peterson
James M
JM
Melton
L Joseph
LJ
D000328:Adult; D000367:Age Factors; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008875:Middle Aged; D011884:Radius / Q000000981:diagnostic imaging*; D012737:Sex Factors; D014057:Tomography, X-Ray Computed / Q000379:methods