Distribution of Axial Compressive Elastic Modulus in Degenerated Intervertebral Discs

Abstract

The objectives of this study were to measure the distribution of axial compressive elastic modulus in the lumbar intervertebral disc and to clarify the differences in distribution between normal and degenerated discs. The authors have proposed a method to measure the local compressive elastic modulus of the intervertebral disc by an indentation test. To estimate the distribution of elastic modulus, sheet specimens were sliced from cadaveric lumbar discs. Two normal and two degenerated discs were utilized to clarify the effect of disc degeneration on the distribution of elastic modulus. The degree of disc degeneration was evaluated macroscopically and radiographically. The distribution of elastic modulus in normal intervertebral discs was symmetric to the midsagittal plane. The elastic modulus in the region of the nucleus pulposus was lower than that of the annulus fibrosus, but was nearly the same as that in the posterolateral regions of the annulus fibrosus. The elastic moduli in the anterior region of the annulus fibrosus were the highest in any area of a disc. In comparison with normal discs, degenerated discs showed asymmetric and irregular distribution of elastic modulus. The elastic moduli of the degenerated nucleus pulposus and annulus fibrosus were much higher than those in the same areas of normal discs.