title: Characterizing microcrack orientation distribution functions in osteonal bone samples.
abstract: Prefailure microdamage in bone tissue is considered to be the most detrimental factor in defining its strength and toughness with respect to age and disease. To understand the influence of microcracks on bone mechanics it is necessary to assess their morphology and three-dimensional distribution. This requirement reaches beyond classic histology and stereology, and methods to obtain such information are currently missing. Therefore, the aim of the study was to develop a methodology that allows to characterize three-dimensional microcrack distributions in bulk bone samples. Four dumbbell-shaped specimens of human cortical bone of a 77-year-old female donor were loaded beyond yield in either tension, compression or torsion (one control). Subsequently, synchrotron radiation micro-computed tomography (SRμCT) was used to obtain phase-contrast images of the damaged samples. A microcrack segmentation algorithm was developed and used to segment microcrack families for which microcrack orientation distribution functions were determined. Distinct microcrack families were observed for each load case that resulted in distinct orientation distribution functions. Microcracks had median areas of approximately 4.7 μm2, 33.3 μm2and 64.0 μm2for tension, compression and torsion. Verifying the segmentation algorithm against a manually segmented ground truth showed good results when comparing the microcrack orientation distribution functions. A size dependence was noted when investigating the orientation distribution functions with respect to the size of the volume of interest used for their determination. Furthermore, a scale separation between tensile, compressive and torsional microcracks was noticeable. Visual comparison to classic histology indicated that microcrack families were successfully distinguished. We propose a methodology to analyse three-dimensional microcrack distributions in overloaded cortical bone. Such information could improve our understanding of bone microdamage and its impact on bone failure in relation to tissue age and disease.
authors.affiliation: School of Engineering and Physical Science, Institute for Mechanical, Process and Energy Engineering, Heriot-Watt University, United Kingdom.|Institute for Surgical Technology and Biomechanics, University of Bern, Switzerland.
authors.forename: U
authors.initials: U
authors.lastname: Wolfram
authors.affiliation: Institute for Surgical Technology and Biomechanics, University of Bern, Switzerland.|Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Switzerland.
authors.forename: J J
authors.initials: JJ
authors.lastname: Schwiedrzik
authors.affiliation: Institute for Surgical Technology and Biomechanics, University of Bern, Switzerland.
authors.forename: M J
authors.initials: MJ
authors.lastname: Mirzaali
authors.affiliation: Institute for Surgical Technology and Biomechanics, University of Bern, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Bürki
authors.affiliation: AO Research Institute, Davos, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Varga
authors.affiliation: European Synchrotron Radiation Facility, Beamline ID 19, France.|CREATIS, University of Lyon, INSA Lyon, UCBL CNRS 5220, Inserm U1206, Creatis, France.
authors.forename: C
authors.initials: C
authors.lastname: Olivier
authors.affiliation: European Synchrotron Radiation Facility, Beamline ID 19, France.|CREATIS, University of Lyon, INSA Lyon, UCBL CNRS 5220, Inserm U1206, Creatis, France.
authors.forename: F
authors.initials: F
authors.lastname: Peyrin
authors.affiliation: Institute for Surgical Technology and Biomechanics, University of Bern, Switzerland.
authors.forename: P K
authors.initials: PK
authors.lastname: Zysset
mesh_terms: D000368:Aged; D000465:Algorithms; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D005260:Female; D006801:Humans; D014057:Tomography, X-Ray Computed
keywords: Cortical bone; X-ray phase micro-tomography; microcrack segmentation; microdamage; orientation distribution function; synchrotron radiation