Geometric Changes in a Lumbar Disc Have a Greater Effect on Disc Biomechanics Than Changes in the Biomechanical Properties of the Disc

Structural alterations of the disc are accompanied by changes in disc tissue structure and composition during degeneration processes. As the lumbar disc degenerates, the disc height decreases. At the same time due to the development of fissures and cracks in the annulus, its material behavior changes. The degeneration process also includes cleft formation in the nucleus and reduction in water content in the nucleus. The clear demarcation between nucleus and surrounding annulus slowly disappear as the disc degeneration progresses thus increasing the annulus volume while reducing the nucleus volume. Both in-vitro and finite element studies exist in literature which deals with the biomechanical effect of disc degeneration. The changes in biomechanical behavior due to degeneration are a combined effect of change in geometrical parameters of the disc and change in material characteristics of the disc components. It is not known whether the change in disc geometries or the change in disc material properties has a predominant effect in altering the disc biomechanics. The current study focuses on this aspect.