title: Sex differences of human trabecular bone microstructure in aging are site-dependent.
abstract: In this study, we characterize bone microstructure, specifically sex differences, at multiple skeletal sites in 165 subjects >52 yr of age, using microCT technology in vitro. Significant sex differences are observed at the distal radius, femoral neck, and femoral trochanter, but not at the iliac crest, calcaneus, and lumbar vertebral body. Correlations in BV/TV between sites ranged from r = 0.13 to 0.56.
  
  
  BACKGROUND
  The goals of this study were (1) to assess potential sex differences of bone microstructure and their difference between skeletal sites and (2) to explore the relationship of trabecular microstructural properties between relevant skeletal sites.
  
  
  METHODS
  Trabecular bone microstructural properties were measured in vitro in 165 subjects 52-99 yr of age using microCT. Defined volumes of interest (cylinders with 6 mm diameter and 6 mm length) were scanned at a resolution of 26 microm (isotropic) in six different anatomical sites: distal radius, femoral neck and trochanter, iliac crest, calcaneus, and second lumbar vertebral body.
  
  
  RESULTS
  At the radius and femoral neck, trabecular bone displayed a more plate-like structure, thicker trabeculae, smaller separation/higher trabecular number, higher connectivity, and a higher degree of anisotropy in men than in women (p < 0.05). At the trochanter, men displayed more plate-like structure and thicker trabeculae (p < 0.05), but no differences in trabecular separation or other parameters compared with the women. At the calcaneus, iliac crest, and second lumbar vertebra none of the bone parameters displayed significant differences between sexes. The BV/TV at one site explained a range of only 2-32% of the variability at other sites.
  
  
  CONCLUSIONS
  These results suggest that trabecular bone microstructural properties are remarkably heterogeneous throughout the skeleton. Significant differences between men and women are observed at some, but not at all, sites. The magnitude of sex differences in trabecular microstructure coincides with that of fracture incidence observed for some of the sites in epidemiological studies.
authors.affiliation: Institute of Anatomy and Musculoskeletal Research, Paracelsus Medical University, Salzburg, Austria. felix.eckstein@pmu.ac.at
authors.forename: Felix
authors.initials: F
authors.lastname: Eckstein
authors.forename: Maiko
authors.initials: M
authors.lastname: Matsuura
authors.forename: Volker
authors.initials: V
authors.lastname: Kuhn
authors.forename: Mathias
authors.initials: M
authors.lastname: Priemel
authors.forename: Ralph
authors.initials: R
authors.lastname: Müller
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Link
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Lochmüller
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D016880:Anisotropy; D001842:Bone and Bones / Q000033:anatomy & histology*; D002111:Calcaneus / Q000033:anatomy & histology; D005260:Female; D005269:Femur / Q000033:anatomy & histology; D005272:Femur Neck / Q000033:anatomy & histology; D006801:Humans; D007085:Ilium / Q000033:anatomy & histology; D008159:Lumbar Vertebrae / Q000033:anatomy & histology; D008297:Male; D008875:Middle Aged; D011884:Radius / Q000033:anatomy & histology; D012737:Sex Factors; D014057:Tomography, X-Ray Computed