title: Simulation of inhomogeneous rather than homogeneous poroelastic tissue material properties within disc annulus and nucleus better predicts cervical spine response: a C3-T1 finite element model analysis under compression and moment loadings.
abstract: METHODS
  A finite element (FE) modeling of homogeneous and inhomogeneous poroelastic tissue material properties within disc anulus fibrosus (AF) and nucleus pulposus (NP).
  
  
  OBJECTIVE
  To test the hypothesis that simulation of inhomogeneous poroelastic tissue material properties within AF and NP quadrants, rather than homogeneous properties within regions of AF and NP without quadrants, would better predict the cervical spine biomechanics.
  
  
  BACKGROUND
  In order to represent tissue swelling and creep deformation behavior more physiologically in FE models, disc poroelastic tissue material properties should be modeled appropriately. Past studies show an existence of inhomogeneous rather than homogeneous nature of the tissue properties in various quadrants of AF and NP, and this has been simulated in a single-segment FE lumbar model with only compression analysis. This article simulated these tissue properties in a multisegmental cervical spine and reported the results of both compression and moment loads.
  
  
  METHODS
  Two three-dimensional FE models of a C3-T1 segment were developed. Model I included homogeneous poroelastic tissue properties in AF and NP, whereas Model II included inhomogeneous poroelastic tissue properties in AF and NP quadrants. Biomechanical responses of the FE models under diurnal compression and moment loads were compared with corresponding in vivo published studies.
  
  
  RESULTS
  Model II with disc quadrant-based inhomogeneous poroelastic tissue properties predicted better, mainly in flexion and extension, than the Model I with homogeneous tissue properties when compared with the corresponding in vivo results, thereby confirming the current study hypothesis. Inhomogeneous tissue properties govern segmental behavior mainly during sagittal plane motions, with a root-mean-square difference of nearly 50% across the motion segments.
  
  
  CONCLUSIONS
  The current data justify the need to simulate inhomogeneous tissue properties within disc quadrants for any FE model analysis. Model II can be further used to understand the biomechanical effects of quadrant-based degenerative poroelastic tissue properties on cervical spine behavior. Future experiments are necessary to support the current study results.
authors.affiliation: Division of Research, Logan University, Chesterfield, MO, USA. mozammil.hussain@logan.edu
authors.forename: Mozammil
authors.initials: M
authors.lastname: Hussain
authors.forename: Raghu N
authors.initials: RN
authors.lastname: Natarajan
authors.forename: Gulafsha
authors.initials: G
authors.lastname: Chaudhary
authors.forename: Howard S
authors.initials: HS
authors.lastname: An
authors.forename: Gunnar B
authors.initials: GB
authors.lastname: Andersson
mesh_terms: D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000502:physiology*; D003198:Computer Simulation; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D055959:Intervertebral Disc Degeneration / Q000503:physiopathology; D008954:Models, Biological; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000502:physiology; D016474:Weight-Bearing