title: Prediction of bone strength at the distal tibia by HR-pQCT and DXA.
abstract: BACKGROUND
  Areal bone mineral density (aBMD) at the distal tibia, measured at the epiphysis (T-EPI) and diaphysis (T-DIA), is predictive for fracture risk. Structural bone parameters evaluated at the distal tibia by high resolution peripheral quantitative computed tomography (HR-pQCT) displayed differences between healthy and fracture patients. With its simple geometry, T-DIA may allow investigating the correlation between bone structural parameter and bone strength.
  
  
  METHODS
  Anatomical tibiae were examined ex vivo by DXA (aBMD) and HR-pQCT (volumetric BMD (vBMD) and bone microstructural parameters). Cortical thickness (CTh) and polar moment of inertia (pMOI) were derived from DXA measurements. Finally, an index combining material (BMD) and mechanical property (polar moment of inertia, pMOI) was defined and analyzed for correlation with torque at failure and stiffness values obtained by biomechanical testing.
  
  
  RESULTS
  Areal BMD predicted the vBMD at T-EPI and T-DIA. A high correlation was found between aBMD and microstructural parameters at T-EPIas well as between aBMD and CTh at T-DIA. Finally, at T-DIA both indexes combining BMD and pMOI were strongly and comparably correlated with torque at failure and bone stiffness.
  
  
  CONCLUSIONS
  Ex vivo, at the distal tibial diaphysis, a novel index combining BMD and pMOI, which can be calculated directly from a single DXA measurement, predicted bone strength and stiffness better than either parameter alone and with an order of magnitude comparable to that of HR-pQCT. Whether this index is suitable for better prediction of fracture risk in vivo deserves further investigation.
authors.affiliation: AO Research Institute Davos, Switzerland. albrecht.popp@aofoundation.org
authors.forename: Albrecht W
authors.initials: AW
authors.lastname: Popp
authors.forename: Markus
authors.initials: M
authors.lastname: Windolf
authors.forename: Christoph
authors.initials: C
authors.lastname: Senn
authors.forename: Andrea
authors.initials: A
authors.lastname: Tami
authors.forename: R Geoff
authors.initials: RG
authors.lastname: Richards
authors.forename: Stefano
authors.initials: S
authors.lastname: Brianza
authors.forename: Damiano
authors.initials: D
authors.lastname: Schiuma
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods*; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D002102:Cadaver; D005260:Female; D050723:Fractures, Bone / Q000000981:diagnostic imaging; D006801:Humans; D013314:Stress, Mechanical; D013977:Tibia / Q000000981:diagnostic imaging* / Q000648:ultrastructure*; D014057:Tomography, X-Ray Computed / Q000379:methods*