title: Morphology based anisotropic finite element models of the proximal femur validated with experimental data.
abstract: Finite element analysis (FEA) of bones scanned with Quantitative Computed Tomography (QCT) can improve early detection of osteoporosis. The accuracy of these models partially depends on the assigned material properties, but anisotropy of the trabecular bone cannot be fully captured due to insufficient resolution of QCT. The inclusion of anisotropy measured from high resolution peripheral QCT (HR-pQCT) could potentially improve QCT-based FEA of the femur, although no improvements have yet been demonstrated in previous experimental studies. This study analyzed the effects of adding anisotropy to clinical resolution femur models by constructing six sets of FE models (two isotropic and four anisotropic) for each specimen from a set of sixteen femurs that were experimentally tested in sideways fall loading with a strain gauge on the superior femoral neck. Two different modulus-density relationships were tested, both with and without anisotropy derived from mean intercept length analysis of HR-pQCT scans. Comparing iso- and anisotropic models to the experimental data resulted in nearly identical correlation and highly similar linear regressions for both whole bone stiffness and strain gauge measurements. Anisotropic models contained consistently greater principal compressive strains, approximately 14% in magnitude, in certain internal elements located in the femoral neck, greater trochanter, and femoral head. In summary, anisotropy had minimal impact on macroscopic measurements, but did alter internal strain behavior. This suggests that organ level QCT-based FE models measuring femoral stiffness have little to gain from the addition of anisotropy, but studies considering failure of internal structures should consider including anisotropy to their models.
authors.affiliation: Institute for Biomechanics, ETH-Zürich, Switzerland. Electronic address: williame@ethz.ch.
authors.forename: W S
authors.initials: WS
authors.lastname: Enns-Bray
authors.affiliation: Institute for Biomechanics, ETH-Zürich, Switzerland; Orthopaedic and Injury Biomechanics Group, University of British Columbia, Vancouver, Canada; Centre for Hip Health and Mobility, University of British Columbia, Vancouver, Canada; Department of Mechanical Engineering, University of British Columbia, Vancouver, Canada.
authors.forename: O
authors.initials: O
authors.lastname: Ariza
authors.affiliation: Orthopaedic and Injury Biomechanics Group, University of British Columbia, Vancouver, Canada; Centre for Hip Health and Mobility, University of British Columbia, Vancouver, Canada; Department of Mechanical Engineering, University of British Columbia, Vancouver, Canada; Department of Orthopedics, University of British Columbia, Vancouver, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Gilchrist
authors.affiliation: Institute for Biomechanics, ETH-Zürich, Switzerland.
authors.forename: R P
authors.initials: RP
authors.lastname: Widmer Soyka
authors.affiliation: Institute for Biomechanics, ETH-Zürich, Switzerland.
authors.forename: P J
authors.initials: PJ
authors.lastname: Vogt
authors.affiliation: Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, School of Engineering and Natural Sciences, University of Iceland, Reykjavik, Iceland.
authors.forename: H
authors.initials: H
authors.lastname: Palsson
authors.affiliation: Department of Radiology, Faculty of Medicine, McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, Canada.
authors.forename: S K
authors.initials: SK
authors.lastname: Boyd
authors.affiliation: Centre for Hip Health and Mobility, University of British Columbia, Vancouver, Canada; Department of Orthopedics, University of British Columbia, Vancouver, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Guy
authors.affiliation: Orthopaedic and Injury Biomechanics Group, University of British Columbia, Vancouver, Canada; Centre for Hip Health and Mobility, University of British Columbia, Vancouver, Canada; Department of Mechanical Engineering, University of British Columbia, Vancouver, Canada; Department of Orthopedics, University of British Columbia, Vancouver, Canada.
authors.forename: P A
authors.initials: PA
authors.lastname: Cripton
authors.affiliation: Institute for Biomechanics, ETH-Zürich, Switzerland.
authors.forename: S J
authors.initials: SJ
authors.lastname: Ferguson
authors.affiliation: Institute for Biomechanics, ETH-Zürich, Switzerland.
authors.forename: B
authors.initials: B
authors.lastname: Helgason
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016880:Anisotropy; D055119:Elastic Modulus; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging; D020342:Finite Element Analysis; D006801:Humans; D008297:Male; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed
keywords: Anisotropy; Computed tomography; Femur; Finite element; Sideways fall