Finite element analysis and materials characterization of changes due to aging and degeneration of the human intervertebral disc.

摘要

Intervertebral disc (IVD) degeneration occurs with aging, and may be a major cause of back pain. Alterations in major biochemical constituents of the IVD have been shown to coincide with aging and degeneration, and can subsequently alter the disc's ability to support load. A significant biochemical change that takes place in degeneration is the loss of proteoglycans (PGs) in the nucleus pulposus (NP). PGs work to resist mechanical forces in the NP through hydration of the molecules, providing hydrostatic pressure to the annulus fibrosus (AF).;Poroelastic theory with osmotic swelling, created for the simulation of articular cartilage, is applied to a finite element model (FEM) of a human IVD throughout a daily loading cycle. The model was validated against experimental studies of axial displacement, radial bulge, and fluid volume lost. The incorporation of osmotic swelling allows for the study of the effect of PGs on the mechanics of the IVD.;In this study, the IVD FEM is created and validated, and the response of the model to a diurnal loading cycle is investigated. Various degrees of degeneration are examined, as well as the intervention techniques of a hydrogel NP replacement implant and the restoration of the PG content in the IVD for the restoration of degenerated discs. A NP hydrogel replacement decreases the stresses in the AF, and restoration of the PG content reduces stresses in both the NP and AF, which may lead to deceleration of the degenerative process.;To develop a more reliable and possibly diagnostic tool for the determination of IVD biomolecular components, Fourier transform infrared (FTIR) spectroscopy is investigated for the analysis of IVD tissue. The results of the study suggest FTIR as a dependable method for quantifying degeneration.;The model developed here provides a novel tool for the investigation of IVD tissue mechanics through the diurnal cycle. The incorporation of poroelastic components allows for the investigation of key biomolecular changes that as demonstrated have a marked effect on IVD mechanics. Accurate determination of biomolecular changes in the IVD will allow for a physiologically relevant model to be developed and possible detection of earlier intervention points.