title: Determinants of forearm strength in postmenopausal women.
abstract: Bone strength at the ultradistal radius, quantified by micro-finite element modeling, can be predicted by variables obtained from high-resolution peripheral quantitative computed tomography scans. The specific formula for this bone strength surrogate (-555.2 + 8.1 × [trabecular vBMD] + 19.6 × [cortical area] + 4.2 × [total cross-sectional area]) should be validated and tested in fracture risk assessment.
  
  
  BACKGROUND
  The purpose of this study was to identify key determinants of ultradistal radius (UDR) strength and evaluate their relationships with age, sex steroid levels, and measures of habitual skeletal loading.
  
  
  METHODS
  UDR failure load (~strength) was assessed by micro-finite element (μFE) modeling in 105 postmenopausal controls from an earlier forearm fracture case-control study. Predictors of bone strength obtained by high-resolution peripheral quantitative computed tomography (HRpQCT) in this group were then evaluated in a population-based cohort of 214 postmenopausal women. Sex steroids were measured by mass spectrometry.
  
  
  RESULTS
  A surrogate variable (-555.2 + 8.1 × [trabecular vBMD] + 19.6 × [cortical area] + 4.2 × [total cross-sectional area]) predicted UDR strength modeled by μFE (R(2) = 0.81), and all parameters except total cross-sectional area declined with age. Evaluated cross-sectionally, the 21% fall in predicted bone strength between ages 40-49 years and 80+ years more resembled the change in trabecular volumetric bone mineral density (vBMD) (-15%) than that in cortical area (-41%). In multivariable analyses, measures of body composition and physical activity were stronger predictors of UDR trabecular vBMD, cortical area, total cross-sectional area, and predicted bone strength than were sex steroid levels, but bio-available estradiol and testosterone were correlated with body mass.
  
  
  CONCLUSIONS
  Bone strength at the UDR, as quantified by μFE, can be predicted from variables obtained by HRpQCT. Predicted bone strength declines with age with changes in UDR trabecular vBMD and cortical area, related in turn to reduced skeletal loading and sex steroid levels. The predicted bone strength formula should be validated and tested in fracture risk assessment.
authors.affiliation: Division of Epidemiology, Department of Health Sciences Research, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA. melton.j@mayo.edu
authors.forename: L J
authors.initials: LJ
authors.lastname: Melton
authors.forename: B L
authors.initials: BL
authors.lastname: Riggs
authors.forename: R
authors.initials: R
authors.lastname: Müller
authors.forename: S J
authors.initials: SJ
authors.lastname: Achenbach
authors.forename: D
authors.initials: D
authors.lastname: Christen
authors.forename: E J
authors.initials: EJ
authors.lastname: Atkinson
authors.forename: S
authors.initials: S
authors.lastname: Amin
authors.forename: S
authors.initials: S
authors.lastname: Khosla
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density / Q000502:physiology; D016022:Case-Control Studies; D005260:Female; D020342:Finite Element Analysis; D005542:Forearm / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D012739:Gonadal Steroid Hormones / Q000032:analysis; D006801:Humans; D013058:Mass Spectrometry; D008875:Middle Aged; D008954:Models, Biological; D017698:Postmenopause; D011884:Radius / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D012307:Risk Factors; D012737:Sex Factors; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D012739:Gonadal Steroid Hormones