THE EFFECT OF FLUID LOSS ON THE VISCOELASTIC BEHAVIOR OF THE LUMBAR INTERVERTEBRAL DISC IN COMPRESSION

A viscoelastic finite element model of a L2-L3 motion segment was cons tructed and used to study: (1) the behavior of the intervertebral disc with different amounts of nucleus fluid loss; and (2) the effect of d ifferent rates of fluid loss on the viscoelastic behavior of the disc. The results indicate that: (1) The viscoelastic behavior of the inter vertebral disc depends to a large extent on the rate of fluid loss fro m the disc; the intrinsic properties of disc tissue play a role only a t the early stage of compressive loading; (2) the axial drain increase s, whereas the intradiscal pressure and the posterio radial disc bulge decrease with increasing fluid loss; (3) a decreasing fluid loss rate with a total fluid lass of 10 to 20 percent (from the nucleus) during the first hour of compressive loading best predicts the overall visco elastic behavior elf a disc.