Heterogeneity of yield strain in low-density versus high-density human trabecular bone |
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| Authors: | Grant Bevill Farhad Farhamand Tony M Keaveny |
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| Institution: | 1. Orthopaedic Biomechanics Laboratory, Department of Mechanical Engineering, University of California, Berkeley, CA, USA;2. Department of Bioengineering, University of California, Berkeley, CA, USA;1. Prisme Institute – MMH, 8, Rue Leonard de Vinci, 45072 Orleans cedex 2, France;2. Bioengineering Science Research Group, School of Engineering Science, Southampton SO17, 1BJ, UK;1. Bone Bioengineering Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY, USA;2. McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA, USA;3. Cartilage Bioengineering Laboratory, Department of Mechanical Engineering, University of Delaware, Newark, DE, USA;4. Department of Orthopaedic Surgery, University of California, San Francisco, CA, USA;5. Orthopaedic Biomechanics Laboratory, Department of Mechanical Engineering, University of California, Berkeley, CA, USA;1. Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands;2. Laboratorio di Tecnologia Medica, Istituti Ortopedici Rizzoli, Bologna, Italy;1. LEMTA, Université de Lorraine, 2, Avenue de la Forêt de Haye, TSA 60604, 54518 Vand?uvre-lès-Nancy Cedex, France;2. Department of Industrial Engineering, Faculty of Engineering, Fayoum University, Fayoum 63514, Egypt;1. Div. of Applied Materials Science, Dept. of Engineering Sciences, Uppsala University, Sweden;2. Solid Mechanics, Dept. of Engineering Sciences, Uppsala University, Sweden;3. Institute for Biomechanics, ETH Zürich, Switzerland |
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| 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° or 45° (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 (R2=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. |
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