Quantitative analysis of surface strains distribution before and after intervertebral disc degeneration

Intervertebral Disc (IVD) degeneration alters disc hydration and height, possibly adversely affecting the structural integrity and the biomechanical behaviour of the other spinal structures, such as the adjacent vertebrae. Exploring the consequences of these alterations on surface IVDs strains patterns may pave the way to predict risk of failure in the vertebral bone and understand its possible correlation to IVD degeneration. In this study, I aimed to investigate how the intervertebral disc (IVD) degeneration can affect the mechanical response of human spine segments, measuring in vitro the three-dimensional surface strain distributions. Two human multi-vertebrae (T9-L1) spine segments were prepared. Mechanical tests were carried out under different loading conditions (flexion, left and right lateral bending, compression) in elastic regime, before and after T11-T12 IVD degeneration. Full-field surface minimum principal strains were measured by means of the contact-less Digital Image Correlation (DIC) technique. Comparative analysis of the global and local minimum principal strains before and after disc degeneration were performed through a home-made MATLAB script. A local quantitative analysis on three Regions of Interest (ROIs, left, central, right) over the disc surfaces has been performed. Disc degeneration leads the degenerated disc to experience larger strains with respect to the adjacent control. Results showed that the most deformed regions experienced larger strains in relation to the loading condition applied. These outcomes, together with an objective evaluation of the disc degenerative state, could be a valuable source for improving spinal implants, developing prevention strategies and paving the way to new clinical treatments.