title: Biomechanical and fluid flowing characteristics of intervertebral disc of lumbar spine predicted by poroelastic finite element method.
abstract: OBJECTIVE
  This study is to reveal the deformation of intervertebral disc (IVD), the stress distribution of solid phase and liquid phase, the variation of fluid flux and flow velocity in lumbar spine and the influence of different permeability parameters on them under intermittent compressive loading.
  
  
  METHODS
  A poroelastic FEM of L4-L5 is assigned with different permeability parameters to analyze the deformation, stress distribution and fluid convection under intermittent compressive loads.
  
  
  RESULTS
  The results show that the pore pressure of IVD decreases with time, but the effective stress increases under intermittent compressive loads. The axial and radial strain will increase and fluid loss will recover at a more rapid rate if the permeability of endplate increases during unloading period. The velocity vectors show that most of the liquid in the disc flows into vertebrae through endplates and only a small quantity of liquid flows through the annulus fibrosus at the loading step, however, at the unloading step, almost all the liquid flowing into IVD is through the endplates.
  
  
  CONCLUSIONS
  The changing rate of pore pressure and effective stresses of nucleus pulposus and annulus fibrosus with higher permeability is smaller than that with smaller permeability. The degenerated endplate (with low permeability) yields high flow velocity decreasing gradient, which might impede liquid inflowing/outflowing smoothly through the endplates. The fluid flowing velocity in loading phase is faster than that in unloading phase, so a short resting time can relieve fatigue, but could not recover to the original liquid condition in IVDs.
authors.affiliation: School of Mechanical Engineering and Automation, Northeastern University, Shenyang, 110819, China.
authors.forename: Li-Xin
authors.initials: LX
authors.lastname: Guo
authors.affiliation: School of Mechanical Engineering and Automation, Northeastern University, Shenyang, 110819, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Li
authors.affiliation: Interdisciplinary Division of Biomedical Engineering, The Hong Kong Polytechnic University, Hong Kong, China.
authors.forename: Ming
authors.initials: M
authors.lastname: Zhang
mesh_terms: D000070616:Annulus Fibrosus / Q000502:physiology; D001696:Biomechanical Phenomena; D004548:Elasticity; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D008159:Lumbar Vertebrae / Q000502:physiology*; D008954:Models, Biological; D000070614:Nucleus Pulposus / Q000502:physiology; D016062:Porosity; D011312:Pressure; D015203:Reproducibility of Results; D012212:Rheology; D013314:Stress, Mechanical; D016474:Weight-Bearing