A structural description for severe degeneration of intervertebral discs to computationally interpret experimental results obtained by stress profilometry.

In this paper, reduction of load carrying capacity in severely degenerated intervertebral discs (IVDs) was attributed to structural damage to the tissues involved with IVDs. Damage to the collagen fibers was blamed for degradation of the annulus fibrosus (AF) and dehydration of nucleus pulposus (NP) was adopted for losing its incompressibility and unstable migration in a degenerated condition. The change of the mechanical properties in the tissues due to degeneration was referred to various experimental reports that were used to simulate a computational model from a lumbar vertebral segment for a patient with degenerated IVDs. In the first phase of the study, the most accurate mechanical properties, suggested for the tissues by the various references, were selected for simulation of the stress diagrams, obtained by stress profilometry. Then in the second phase, reliability of some damage scenarios according to the pathophysiological descriptions for the tissues in a severely degenerated condition was examined. The results of the model showed that the incompressible response of NP which was taking 79% of a compression load for a normal condition of IVD, took just 40% of the load in a degenerated condition. The models postulated the residual stiffness of a severely degenerated IVD equal to 13% of its original value.