The Effect of Fluid Loss on the Viscoelastic Behavior of the Lumbar Intrevertebral Disc in Compression

Abstract

A viscoelastic finite element model of a L2-L3 motion segment was constructed and used to study: (1) the behavior of the intervertebral disc with different amounts of nucleus fluid loss; and (2) the effect of different rates of fluid loss on the viscoelastic behavior of the disc. The results indicate that: (1) The viscoelastic behavior of the intervertebral disc depends to a large extent on the rate of fluid loss from the disc; the intrinsic properties of disc tissue play a role only at the early stage of compressive loading; (2) the axial strain increases, whereas the intradiscal pressure and the posterior radial disc bulge decrease with increasing fluid loss; (3) a decreasing fluid loss rate with a total fluid loss of 10 to 20 percent (from the nucleus) during the first hour of compressive loading best predicts the overall viscoelastic behavior of a disc.

Viscoelastic Responses of the Lumbar Spine during Prolonged Stooping

“…As prolonged static work postures have been identified as a risk factor for low back pain, viscoelastic FEA models of the intervertebral disc or spine segment have been developed to investigate the time-dependent deformation or stress in the lumbar spine components. Recent studies that incorporated viscoelastic properties into FEA models often used the Prony series or nonlinear spring-dashpot models to simulate the viscoelastic behavior of the disc components and ligaments (Wang et al, 1997;Wang et al, 1999;Wang et al, 2000;Lu et al, 1998). Wang et al (1997Wang et al ( , 1999Wang et al ( , and 2000 applied the Zener model vertebra.…”

“…Results found that the stress distribution in the discs differed considerably when the muscle forces are neglected, indicating that muscle forces should not be neglected when studying the stresses in the lumbar spine. examined viscoelastic responses of the lumbar spine without muscles (Wang et al, 1997;Wang et al, 2000;Cheung et al, 2003;Lu et al, 1998) or elastic behaviors with muscles (Zander et al, 2001;Goel et al, 1993;Shirazi-Adl et al, 2002). No FE model of a whole lumbar spine with full nonlinear and viscoelastic material properties has been created for the analysis of mechanical responses during prolonged stooping.…”

“…Recent FE models have incorporated viscoelastic material properties for the disc components and spinal ligaments to simulate time-dependent behaviors of the lumbar motion segment (Lu et al, 1998;Wang et al, 2000;Wang et al, 1997;Cheung et al, 2003).…”

“…Viscoelastic material properties of disc components and spinal ligaments from in vitro tissue experiments were incorporated into the FE models to study the viscoelastic responses of a single motion segment under constant creep compression load (Wang et al, 1997;Lu et al, 1998;Cheung et al, 2003), vibrational compression load (Cheung et al, 2003), and static sagittal flexion load with varying flexion speed (Wang et al, 2000). Results of these models suggested that consideration of the viscoelastic material properties of passive tissues is essential to studying mechanical behaviors of a motion segment (Wang et al, 2000).…”

“…A study of prolonged stooping requires the creation of a 3D FE model of the lumbar spine with viscoelastic ligaments and extensor muscles in order to examine time and posture-dependent changes in the relationship between ligaments and muscles in maintaining lumbar stability and supporting upper body weight as well as global geometry of the lumbar spine. Previous FEA models have looked at viscoelastic responses of the lumbar spine without muscles (Wang et al, 1997;Wang et al, 2000;Cheung et al, 2003;Lu et al, 1998) or elastic behaviors with muscles (Zander et al, 2001;Goel et al, 1993;Shirazi-Adl et al, 2002).…”