Morphological and Mechanical Analysis of the Porous Structure of Cortical Bone

Introduction: Bone is a complex hierarchical material that can be studied at many levels. For diseases like osteoporosis, characterized by bone loss, macro-level tests like DEXA scanning can predict an increased fracture risk, but cannot detect the driving mechanism. As a porous, anisotropic material, one of the only ways to truly predict bone mechanics is to model the underlying microstructure. The complexity of the porous structure of cortical bone presents a challenge when generating computational models requiring high resolution imaging, advanced mesh generation algorithms, and powerful computational resources for finite element analysis.

Methods: Cortical bone samples were collected from the middle neck of a cadaver femur (71 year old female, no history of bone disease). The neck was separated into four quadrants: anterior, posterior, superior, and inferior then further sub-sectioned to 5 mm pieces. Microcomputed tomography scans were collected (4 µm/voxel), processed, and used to generate 3D models of the bone and of the porous network. Effective strain in each model was derived through finite element analysis using physiologic displacement boundary conditions and Young’s modulus estimation using density calibrations from hydroxyapatite phantoms. Two- and three-dimensional geometric measures were evaluated from the processed images.

Results: For all quadrants, no significant relationship was found between the threedimensional measures and the effective strain around pores in a two-dimensional cross section. Effective strain increased significantly with area, shape factor, and clustering, however, these relationships were not strong.

Discussion: Studying the microstructure of cortical bone is useful for identifying the exact location of bone growth and repair based on mechanical stimulus. Relating microstrain and bone formation is important in developing a stronger understanding of how bone adapts. This knowledge could be used to develop training protocols for those susceptible to bone loss such as postmenopausal women and astronauts.

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Year

Entry

1965

Atkinson PJ. Changes in resorption spaces in femoral cortical bone with age. J Pathol Bacteriol. January 1965;89(1):173-178.

2007

Schneider P, Stauber M, Voide R, Stampanoni M, Donahue LR, Müller R. Ultrastructural properties in cortical bone vary greatly in two inbred strains of mice as assessed by synchrotron light based micro‐ and nano‐CT. J Bone Miner Res. October 2007;22(10):1557-1570.

1994

Parfitt AM. Osteonal and hemi‐osteonal remodeling: the spatial and temporal framework for signal traffic in adult human bone. J Cell Biochem. July 1994;55(3):273-286.

2002

Pistoia W, van Rietbergen B, Lochmüller E-M, Lill CA, Eckstein F, Rüegsegger P. Estimation of distal radius failure load with micro-finite element analysis models based on three-dimensional peripheral quantitative computed tomography images. Bone. June 2002;30(6):842-848.

2016

Legland D, Arganda-Carreras I, Andrey P. MorphoLibJ: integrated library and plugins for mathematical morphology with ImageJ. Bioinformatics. November 15, 2016;32(22):3532-3534.