ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

FINITE ELEMENT ANALYSIS OF MICROSCOPY TENSILE TESTS OF
ANNULUS FIBROSUS TISSUE
B.J. Luxmoore 1 , V. N. Wijayathunga 1 , S. Rehman 1 , K. Wade 2 , S. Rodrigues 2 , N.
Broom 2 and R.K. Wilcox 1
1. ABSTRACT
A histological study of slices of annulus fibrosus tissue was conducted in which the
tissue was loaded in tension in line with the radial direction of the intervertebral disc.
Puckering of the tissue was observed at the interlamellar boundaries, suggesting that
minor bridging elements have stiffer material properties than their surrounding tissue
constituents. The histological study was replicated in a geometrically specimenspecific,
finite element model of the tissue. The material properties of the model were
varied and it was found that the closest match to the experimental results was achieved
with a stiff sheath surrounding the fibre bundles.
2. INTRODUCTION
The intervertebral disc (IVD) consists of a gel-like nucleus pulposus (NP) surrounded
by layers (lamellae) of collagenous fibre bundles with alternating direction. These
layers make up the annulus fibrosus (AF). Recent histological studies have investigated
interlamellar interactions and constituent tissues. Yu et al. 1,2 have suggested minor
bridging elements are part of a interconnected network of sheaths that surrounds
bundles of fibres and extends throughout the AF. Pezowicz et al. 3,4 showed the
puckering of interlamellar boundaries at their intersection with minor bridging elements,
suggesting that they are somehow anchored within the lamella’s fibres. Although these
structural details have been investigated histologically, little is known about the
mechanics of these constituents when under load.
The aim of this study was to elucidate information about tissue structure from
microscopy data that could be incorporated into finite element (FE) models of the AF.
Measurements from microscopy data about the tissue structure and geometry and
observations of the structure under load were used as a foundation to build
geometrically specimen specific models of AF tissue.
The mechanical roles of the minor bridging elements and sheath network were
questioned by representing the biomechanical behaviour of the tissue observed in vitro
in a FE model, with a long term view to implement findings into a full IVD model with
improved representation of interlamellar mechanics.
1
Institute of Medical and Biological Engineering, Department of Mechanical Engineering, University of
Leeds, LS2 9JT, U.K.
2
Department of Chemical and Materials Engineering, University of Auckland, New Zealand