title: Theoretical effects of fully ductile versus fully brittle behaviors of bone tissue on the strength of the human proximal femur and vertebral body.
abstract: The influence of the ductility of bone tissue on whole-bone strength represents a fundamental issue of multi-scale biomechanics. To gain insight, we performed a computational study of 16 human proximal femurs and 12 T9 vertebral bodies, comparing the whole-bone strength for the two hypothetical bounding cases of fully brittle versus fully ductile tissue-level failure behaviors, all other factors, including tissue-level elastic modulus and yield stress, held fixed. For each bone, a finite element model was generated (60-82 μm element size; up to 120 million elements) and was virtually loaded in habitual (stance for femur, compression for vertebra) and non-habitual (sideways fall, only for femur) loading modes. Using a geometrically and materially non-linear model, the tissue was assumed to be either fully brittle or fully ductile. We found that, under habitual loading, changing the tissue behavior from fully ductile to fully brittle reduced whole-bone strength by 38.3±2.4% (mean±SD) and 39.4±1.9% for the femur and vertebra, respectively (p=0.39 for site difference). These reductions were remarkably uniform across bones, but (for the femur) were greater for non-habitual (57.1±4.7%) than habitual loading (p<0.001). At overall structural failure, there was 5-10-fold less failed tissue for the fully brittle than fully ductile cases. These theoretical results suggest that the whole-bone strength of the proximal femur and vertebra can vary substantially between fully brittle and fully ductile tissue-level behaviors, an effect that is relatively insensitive to bone morphology but greater for non-habitual loading.
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, CA, USA. Electronic address: shashank@berkeley.edu.
authors.forename: Shashank
authors.initials: S
authors.lastname: Nawathe
authors.affiliation: Department of Basic Medical Sciences, Purdue University, IN, USA.
authors.forename: Haisheng
authors.initials: H
authors.lastname: Yang
authors.affiliation: Department of Orthopaedic Surgery, University of California, San Francisco, CA, USA.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Fields
authors.affiliation: Beth Israel Deaconess Medical Center, Boston, MA, USA.
authors.forename: Mary L
authors.initials: ML
authors.lastname: Bouxsein
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, CA, USA; Department of Bioengineering, University of California, Berkeley, CA, USA. Electronic address: tmk@me.berkeley.edu.
authors.forename: Tony M
authors.initials: TM
authors.lastname: Keaveny
mesh_terms: D000058:Accidental Falls; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000033:anatomy & histology / Q000473:pathology*; D003198:Computer Simulation; D055119:Elastic Modulus; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000473:pathology*; D020342:Finite Element Analysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D013131:Spine / Q000033:anatomy & histology / Q000473:pathology*; D013718:Tensile Strength
keywords: Femur; Fracture; Microstructure; Tissue-level ductility; Whole bone