Effects of degeneration on the elastic modulus distribution in the lumbar intervertebral disc.

Abstract

Local elastic moduli of sliced intervertebral disc specimens were studied after establishing the relation between the elastic modulus and indentation behaviors by model tests using polyurethane specimens. This study presents a method to quantify the distribution of compressive elastic moduli in the lumbar intervertebral disc and to clarify the effects of degeneration on the distribution. No study has been performed to evaluate the distribution of axial compressive elastic moduli, which is supposed to relate previous biomechanical, biological, and biochemical findings regarding the intervertebral disc. Local compressive elastic moduli of the intervertebral disc were estimated by indentation tests. To evaluate the distribution of elastic moduli, indentation tests were performed at nodal points of a 10 mm x 10 mm network on a specimen. Nine cadaveric lumbar discs (L3-L4 and L4-L5) with various degrees of degeneration were tested. The age of subjects ranged 39 to 90 years (mean, 58.4 years). The distribution of elastic moduli in normal discs was symmetric about the midsagittal plane. The mean elastic modulus in the nucleus pulposus was 5.8 kPa and those of the anterior and posterior anulus fibrosus were 110.7 and 75.8 kPa, respectively. The elastic moduli in the lateral portions were the lowest in the normal anulus, and were close to the values of the nucleus. Compared to normal discs, degenerated discs showed irregular distributions of elastic moduli. The elastic moduli of the degenerated nucleus were higher than those in normal discs. The distribution of elastic moduli is much different between discs with and without degeneration.