Yield strain behavior of trabecular bone.
If bone adapts to maintain constant strains and if on-axis yield strains in trabecular bone are independent of apparent density, adaptive remodeling in trabecular bone should maintain a constant safety factor (yield strain/functional strain) during habitual loading. To test the hypothesis that yield strains are indeed independent of density, compressive (n = 22) and tensile (n = 22) yield strains were measured without end-artifacts for low density (0.18 +/- 0.04 g cm(-3)) human vertebral trabecular bone specimens. Loads were applied in the superior-inferior direction along the principal trabecular orientation. These 'on-axis' yield strains were compared to those measured previously for high-density (0.51 +/- 0.06 g cm(-3)) bovine tibial trabecular bone (n = 44). Mean (+/- S.D.) yield strains for the human bone were 0.78 +/- 0.04% in tension and 0.84 +/- 0.06% in compression; corresponding values for the bovine bone were 0.78 +/- 0.04 and 1.09 +/- 0.12%, respectively. Tensile yield strains were independent of the apparent density across the entire density range (human p = 0.40, bovine p = 0.64, pooled p = 0.97). By contrast, compressive yield strains were linearly correlated with apparent density for the human bone (p < 0.001) and the pooled data (p < 0.001), and a suggestive trend existed for the bovine data (p = 0.06). These results refute the hypothesis that on-axis yield strains for trabecular bone are independent of density for compressive loading, although values may appear constant over a narrow density range. On-axis tensile yield strains appear to be independent of both apparent density and anatomic site.
Kopperdahl
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Department of Mechanical Engineering, University of California, Berkeley 94720-1740, USA. kopper@euler.me.berkeley.edu
Keaveny
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D000222:Adaptation, Physiological; D000704:Analysis of Variance; D000818:Animals; D015519:Bone Density; D016723:Bone Remodeling / Q000502:physiology; D001842:Bone and Bones / Q000502:physiology*; D002102:Cadaver; D002417:Cattle; D019245:Compressive Strength; D004548:Elasticity; D006801:Humans; D012044:Regression Analysis; D013131:Spine / Q000502:physiology; D013314:Stress, Mechanical; D013718:Tensile Strength; D013977:Tibia / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology