Characterisation and modelling of spinal facet joints

The spinal facet joints are known to be an important component in the kinematics of the spine and play a role in the load transmission through the spinal vertebrae. Due to the high level of mobility and the large forces influencing the facet joint, it can develop significant degenerative changes which lead to the back pain problems in the human spine. However, the technical difficulties, limitations, ethical concerns and cost involved in experimental studies of human facet joints have driven the use of computational modelling studies. The aim of this study was to characterise the anatomical and biomechanical behaviour of the spinal facet joints and evaluate the use of an ovine facet joint model as a representation of the human facet joint. In the present study, ovine spines were used in order to investigate an animal model to represent the human spine in the facet joint studies. Morphological studies were carried out to determine the facet articular radius and facet orientation angle using an improved method based on micro-computed tomography scan images. Subsequently, the biomechanical properties of the cartilage in the ovine facet joint were characterised using a combination of experimental and computational methods. The similarities of the results obtained between the ovine and human results indicate that the ovine spine would be a good model to represent the human spine in facet joint studies. A novel specimen-specific modelling approach was implemented to model the cartilage specimen since the model could replicate the actual curvature of the cartilage surface and the trabecular architecture of the subchondral bone. The specimen-specific model demonstrated that the cartilage curvature, the elastic modulus of the subchondral bone and trabecular architecture of the subchondral bone, influenced the characterisation of the biphasic properties of the cartilage. The methodologies developed were then applied in a pilot study in human facet joint specimens and recommendations made for future work in this area.