title: Heterogeneity of yield strain in low-density versus high-density human trabecular bone.
abstract: Understanding the off-axis behavior of trabecular yield strains may lend unique insight into the etiology of fractures since yield strains provide measures of failure independent of elastic behavior. We sought to address anisotropy of trabecular yield strains while accounting for variations in both density and anatomic site and to determine the mechanisms governing this behavior. Cylindrical specimens were cored from vertebral bodies (n=22, BV/TV=0.11+/-0.02) and femoral necks (n=28, BV/TV=0.22+/-0.06) with the principal trabecular orientation either aligned along the cylinder axis (on-axis, n=22) or at an oblique angle of 15 degrees or 45 degrees (off-axis, n=28). Each specimen was scanned with micro-CT, mechanically compressed to failure, and analysed with nonlinear micro-CT-based finite element analysis. Yield strains depended on anatomic site (p=0.03, ANOVA), and the effect of off-axis loading was different for the two sites (p=0.04)-yield strains increased for off-axis loading of the vertebral bone (p=0.04), but were isotropic for the femoral bone (p=0.66). With sites pooled together, yield strains were positively correlated with BV/TV for on-axis loading (R(2)=58%, p<0.0001), but no such correlation existed for off-axis loading (p=0.79). Analysis of the modulus-BV/TV and strength-BV/TV relationships indicated that, for the femoral bone, the reduction in strength associated with off-axis loading was greater than that for modulus, while the opposite trend occurred for the vertebral bone. The micro-FE analyses indicated that these trends were due to different failure mechanisms for the two types of bone and the different loading modes. Taken together, these results provide unique insight into the failure behavior of human trabecular bone and highlight the need for a multiaxial failure criterion that accounts for anatomic site and bone volume fraction.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Department of Mechanical Engineering, University of California, Berkeley, CA 94720-1740, USA.
authors.forename: Grant
authors.initials: G
authors.lastname: Bevill
authors.forename: Farhad
authors.initials: F
authors.lastname: Farhamand
authors.forename: Tony M
authors.initials: TM
authors.lastname: Keaveny
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016880:Anisotropy; D015519:Bone Density / Q000502:physiology*; D019245:Compressive Strength / Q000502:physiology; D003198:Computer Simulation; D055119:Elastic Modulus / Q000502:physiology; D005260:Female; D005272:Femur Neck / Q000502:physiology*; D020342:Finite Element Analysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D013131:Spine / Q000502:physiology*; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology*
references.citation: J Orthop Res. 1999 Jul;17(4):582-5
references.pmid: 10459766
references.citation: Acta Orthop Scand. 1980 Jun;51(3):429-37
references.pmid: 7446022
references.citation: J Biomech. 2001 May;34(5):569-77
references.pmid: 11311697
references.citation: J Biomech Eng. 2004 Dec;126(6):677-84
references.pmid: 15796326
references.citation: J Orthop Res. 1985;3(4):424-34
references.pmid: 4067701
references.citation: J Biomech. 1996 Oct;29(10):1309-17
references.pmid: 8884476
references.citation: J Biomech. 1998 Jul;31(7):601-8
references.pmid: 9796682
references.citation: Bone. 1987;8(2):79-85
references.pmid: 3593611
references.citation: J Biomech. 1987;20(11-12):1121-34
references.pmid: 3429458
references.citation: J Biomech Eng. 1986 Feb;108(1):83-8
references.pmid: 3959556
references.citation: J Biomech. 2007;40(8):1670-5
references.pmid: 17368466
references.citation: J Biomech. 2004 Nov;37(11):1671-8
references.pmid: 15388309
references.citation: J Biomech. 2004 Jan;37(1):55-65
references.pmid: 14672568
references.citation: J Biomech. 1987;20(1):29-33
references.pmid: 3558426
references.citation: J Biomech. 1985;18(5):317-28
references.pmid: 4008502
references.citation: J Biomech Eng. 1999 Dec;121(6):629-35
references.pmid: 10633264
references.citation: Bone. 2006 Dec;39(6):1218-25
references.pmid: 16904959
references.citation: J Orthop Res. 1997 Jan;15(1):101-10
references.pmid: 9066533
references.citation: Bone. 1994 Jan-Feb;15(1):105-9
references.pmid: 8024844
references.citation: J Biomech Eng. 1991 Nov;113(4):353-60
references.pmid: 1762430
references.citation: J Biomech. 1982;15(3):155-64
references.pmid: 7096368
references.citation: J Biomech Eng. 1999 Aug;121(4):414-22
references.pmid: 10464696
references.citation: J Biomech. 2005 Jan;38(1):141-4
references.pmid: 15519349
references.citation: J Biomech Eng. 1989 Aug;111(3):256-60
references.pmid: 2779192