title: 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.
  
  
  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.
authors.affiliation: 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
authors.forename: Sundeep
authors.initials: S
authors.lastname: Khosla
authors.forename: B Lawrence
authors.initials: BL
authors.lastname: Riggs
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Atkinson
authors.forename: Ann L
authors.initials: AL
authors.lastname: Oberg
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: McDaniel
authors.forename: Margaret
authors.initials: M
authors.lastname: Holets
authors.forename: James M
authors.initials: JM
authors.lastname: Peterson
authors.forename: L Joseph
authors.initials: LJ
authors.lastname: Melton
mesh_terms: 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