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

FINITE ELEMENT MODELS OF THE INTERVERTEBRAL DISC
DEVELOPED FROM MR SCANS TO INCLUDE LAMELLAR
MECHANICS
B.J. Luxmoore 1 , V. N. Wijayathunga 1 , S. Rehman 1 , R. Hodgson 2 , R. Evans 2 and
R.K. Wilcox 1
1. ABSTRACT
Two magnetic resonance imaging (MRI) sequences were developed to capture the
internal structures of intervertebral disc soft tissues of an ovine specimen in an unloaded
and compressed state, including the geometry and deformation of the lamellae of the
annulus fibrosus. The MRI data was combined with micro computer tomography data
of the adjacent vertebrae to create a specimen specific model that included the soft
tissues. This novel method allows specimen specific models of the internal soft tissues
to be constructed, calibrated and validated. Future work will incorporate of lamellar
mechanics into specimen specific models.
2. INTRODUCTION
Specimen-specific finite element (FE) models of the intervertebral disc (IVD) are not as
advanced as those for hard tissue, partially due to the difficulty in differentiating
between the internal soft tissue structures in image data. Methods for generating
specimen-specific FE models have been developed by combining magnetic resonances
imaging (MRI) and micro computer tomography (µCT) 1,2 . However, techniques that
include details of the internal soft tissue structure, such as the lamellar organisation and
data that can be used for calibration and validation are still lacking. O’Connell and
Elliott 3,4 presented magnetic resonance imaging (MRI) sequences that show the
deformation of the lamellae under compressive loads. However, this image data has not
yet been used in computational simulations.
The aim of this study was to assess the potential of MRI data for model construction,
calibration and validation and to investigate different techniques for generating FE
models of the IVD using a combination of imaging modalities.
Two MRI sequences were tuned to individually image the nucleus pulposus (NP) and
annulus fibrosus (AF) of in vitro ovine specimens in both an unloaded and compressed
state. A specimen specific model was developed directly from MRI and µCT data.
1
Institute of Medical and Biological Engineering, Department of Mechanical Engineering, University of
Leeds, LS2 9JT, U.K.
2
NIHR Leeds Musculoskeletal Biomedical Research Unit, Chapel Allerton Hospital, Leeds Teaching
Hospitals Trust, Leeds, LS7 4SA