Intervertebral disc degeneration: an experimental and numerical study using a rabbit model.

Animal models have been extensively used for the study of degenerative diseases and evaluation of new therapies to stop or even reverse the disease progression. The aim of this study is to reproduce lumbar intervertebral disc degeneration in a rabbit model by performing a percutaneous annular puncture at L4L5 level. The effect of this damage on the spine behaviour was analysed combining three different techniques: imaging processing, mechanical testing and computational modelling. Twenty New Zealand white rabbits were divided into control and experimental groups and followed up during 6 months. Intervertebral disc height, as well as nucleus area and signal intensity, decreased with degeneration while storage and loss moduli increased. Both changes may be related to the loss of water and tissue fibrosis. Similar but slighter changes were reported for adjacent discs. A finite element model was built based on MRI and mechanical testing findings to add new biomechanical information that cannot be obtained experimentally. Four stages were computationally simulated representing the different experimental phases. The numerical simulations showed that compressive stresses in the damaged and adjacent discs were modified with the progression of degeneration. Although extrapolation to humans should be carefully made, the use of numerical animal models combined with an experimental one could give a new insight of the overall mechanical behaviour of the spine.