title: Poor correlation of mid-femoral measurements by CT and hip measurements by DXA in the elderly.
abstract: OBJECTIVE
  Hip fracture is a devastating event in terms of outcome in the elderly, and the best predictor of hip fracture risk is hip bone density, usually measured by dual X-ray absorptiometry (DXA). However, bone density can also be ascertained from computerized tomography (CT) scans, and mid-thigh scans are frequently employed to assess the muscle and fat composition of the lower limb. Therefore, we examined if it was possible to predict hip bone density using mid-femoral bone density.
  
  
  METHODS
  Subjects were 803 ambulatory white and black women and men, aged 70-79 years, participating in the Health, Aging and Body Composition (Health ABC) Study. Bone mineral content (BMC, g) and volumetric bone mineral density (vBMD, mg/cm3) of the mid-femur were obtained by CT, whereas BMC and areal bone mineral density (aBMD, g/cm2) of the hip (femoral neck and trochanter) were derived from DXA.
  
  
  RESULTS
  In regression analyses stratified by race and sex, the coefficient of determination was low with mid-femoral BMC, explaining 6-27% of the variance in hip BMC, with a standard error of estimate (SEE) ranging from 16 to 22% of the mean. For mid-femur vBMD, the variance explained in hip aBMD was 2-17% with a SEE ranging from 15 to 18%. Adjusting aBMD to approximate volumetric density did not improve the relationships. In addition, the utility of fracture prediction was examined. Forty-eight subjects had one or more fractures (various sites) during a mean follow-up of 4.07 years. In logistic regression analysis, there was no association between mid-femoral vBMD and fracture (all fractures), whereas a 1 SD increase in hip BMD was associated with reduced odds for fracture of approximately approximately 60%.
  
  
  CONCLUSIONS
  These results do not support the use of CT-derived mid-femoral vBMD or BMC to predict DXA-measured hip bone mineral status, irrespective of race or sex in older adults. Further, in contrast to femoral neck and trochanter BMD, mid-femur vBMD was not able to predict fracture (all fractures).
authors.affiliation: Epidemiology, Demography and Biometry Program, National Institute on Aging, Bethesda, Maryland, USA. dtaaffe@hms.uq.edu.au
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Taaffe
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Lang
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Harris
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D000368:Aged; D015519:Bone Density; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D006620:Hip Fractures / Q000473:pathology; D006801:Humans; D008297:Male; D011237:Predictive Value of Tests; D012044:Regression Analysis; D013223:Statistics as Topic; D014057:Tomography, X-Ray Computed