Computer Simulation of Microdamage and Microfracture in Vertebral Trabecular Bone

Adam, Clayton J. & Loughran, Jeffrey G. (2007) Computer Simulation of Microdamage and Microfracture in Vertebral Trabecular Bone. In Williamson, Owen (Ed.) Annual Scientific Meeting of the Spine Society of Australia, 20-22 April, 2007, Hobart, Australia.




INTRODUCTION The existence of both diffuse microdamage and discrete microfractures in trabecular bone has been reported on numerous occasions (eg. 1), and healing cracks appear to be a normal feature of trabecular bone response to physiological loads (2). However, while partial cracks lead to callus formation and repair, through-cracks may cause resorption of entire trabeculae due to the loss of strain in the disconnected strut, contributing to long term bone loss and increased risk of gross fracture (3). For these reasons, the biomechanics of trabecular bone microdamage and microfracture are of significant clinical interest. The aim of this study was to investigate trabecular bone microdamage mechanics using combined finite/discrete element numerical modelling techniques.

METHOD Two-dimensional models of rectangular samples of trabecular bone subjected to uniaxial compressive loading were created using Voronoi diagrams and solved using a combined finite/discrete element simulation software package. The chosen mesh parameters resulted in a porosity of ~87%, or bone volume to total volume ratio (BV/TV) of 13.4%. Trabecular bone was represented using an elastic-plastic material model which allowed the bone to fracture when a certain tensile strain was reached. Models were held at the lower edge and loaded in compression at the upper edge. Levels of microdamage and microfracture were assessed by counting the number of struts with either plastic strains or distinct cracks at a given strain level.

RESULTS At an apparent compressive strain of 3%, brittle models showed cracking in up to 8% of the trabecular struts. At lower compressive strain levels, microfractures were randomly distributed throughout the trabecular model. As the compressive strain was increased, cracks rapidly coalesced to form a complete fracture plane through the bone. A much higher proportion of struts experienced 'diffuse' damage (plastic bending) than discrete crack formation. The degree of lateral constraint provided by the surrounding cortical bone was predicted to make a large difference to the apparent elastic modulus (260% higher for a confined than an unconfined cas) and to the maximum compressive stress (90% higher for confined than unconfined case).

DISCUSSION The computer simulations presented in this study represent an initial application of numerical modelling tools to trabecular microfracture mechanics. The geometry used in the models was highly simplified from actual trabecular bone, but the models correctly predicted (i) the onset of microdamage and microfracture in trabecular bone well before apparent yield, (ii) the prevalence of microdamage (plastic bending) over microfracture (cracking) of trabecular struts, (iii) the low proportion of struts fractured even at high compressive strains. There is a need for better material properties to describe the mechanics of trabecular bone, as well as more realistic geometric representation, however we conclude that computer simulation techniques are a potentially valuable predictive tool for better understanding the mechanics of microdamage and microfracture in vertebral trabecular bone.

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ID Code: 7491
Item Type: Conference Paper
Additional Information: For more information contact the author @
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Subjects: Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > BIOMEDICAL ENGINEERING (090300) > Biomechanical Engineering (090302)
Divisions: Past > QUT Faculties & Divisions > Faculty of Built Environment and Engineering
Current > Institutes > Institute of Health and Biomedical Innovation
Deposited On: 10 May 2007
Last Modified: 03 Mar 2011 05:42

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