title: Mapping anisotropy of the proximal femur for enhanced image based finite element analysis.
abstract: Finite element (FE) models of bone derived from quantitative computed tomography (QCT) rely on realistic material properties to accurately predict bone strength. QCT cannot resolve bone microarchitecture, therefore QCT-based FE models lack the anisotropy apparent within the underlying bone tissue. This study proposes a method for mapping femoral anisotropy using high-resolution peripheral quantitative computed tomography (HR-pQCT) scans of human cadaver specimens. Femur HR-pQCT images were sub-divided into numerous overlapping cubic sub-volumes and the local anisotropy was quantified using a 'direct-mechanics' method. The resulting directionality reflected all the major stress lines visible within the trabecular lattice, and provided a realistic estimate of the alignment of Harvesian systems within the cortical compartment. QCT-based FE models of the proximal femur were constructed with isotropic and anisotropic material properties, with directionality interpolated from the map of anisotropy. Models were loaded in a sideways fall configuration and the resulting whole bone stiffness was compared to experimental stiffness and ultimate strength. Anisotropic models were consistently less stiff, but no statistically significant differences in correlation were observed between material models against experimental data. The mean difference in whole bone stiffness between model types was approximately 26%, suggesting that anisotropy can still effect considerable change in the mechanics of proximal femur models. The under prediction of whole bone stiffness in anisotropic models suggests that the orthotropic elastic constants require further investigation. The ability to map mechanical anisotropy from high-resolution images and interpolate information into clinical-resolution models will allow testing of new anisotropic material mapping strategies.
authors.affiliation: Schulich School of Engineering, University of Calgary, Calgary, AB, Canada T2N 4Z6; Roger Jackson Centre for Health and Wellness Research, University of Calgary, Calgary, AB, Canada T2N 4Z6; McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada T2N 4Z6.
authors.forename: William S
authors.initials: WS
authors.lastname: Enns-Bray
authors.affiliation: Schulich School of Engineering, University of Calgary, Calgary, AB, Canada T2N 4Z6; Roger Jackson Centre for Health and Wellness Research, University of Calgary, Calgary, AB, Canada T2N 4Z6; McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada T2N 4Z6.
authors.forename: Jan S
authors.initials: JS
authors.lastname: Owoc
authors.affiliation: Schulich School of Engineering, University of Calgary, Calgary, AB, Canada T2N 4Z6; Roger Jackson Centre for Health and Wellness Research, University of Calgary, Calgary, AB, Canada T2N 4Z6; McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada T2N 4Z6.
authors.forename: Kyle K
authors.initials: KK
authors.lastname: Nishiyama
authors.affiliation: Schulich School of Engineering, University of Calgary, Calgary, AB, Canada T2N 4Z6; Roger Jackson Centre for Health and Wellness Research, University of Calgary, Calgary, AB, Canada T2N 4Z6; McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada T2N 4Z6; Department of Radiology, Faculty of Medicine, University of Calgary, Calgary, AB, Canada T2N 4Z6. Electronic address: skboyd@ucalgary.ca.
authors.forename: Steven K
authors.initials: SK
authors.lastname: Boyd
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016880:Anisotropy; D001696:Biomechanical Phenomena; D005269:Femur / Q000000981:diagnostic imaging*; D020342:Finite Element Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted; D055595:Mechanical Phenomena; D008875:Middle Aged; D014057:Tomography, X-Ray Computed
keywords: Anisotropy; Bone; Computed tomography; Finite element; Proximal femur