title: Prediction of peripheral tears in the anulus of the intervertebral disc.
abstract: METHODS
  The mechanical behavior of age-related degeneration in the anulus of lumbar spine segments was investigated under extension with compressive preload by the finite-element method.
  
  
  OBJECTIVE
  To investigate why peripheral tears are initiated in the anterior outer anulus in the early stage of life.
  
  
  BACKGROUND
  Age-related changes in the geometry, loading conditions, and material-mechanical properties of lumbar spine would change mechanical behavior of the anulus.
  
  
  METHODS
  Two finite element models of the human lumbar segments (L3-L4), a young spine model for young adults and an old spine model for elder adults, were constructed. The anulus was modeled as laminate composite elements with 16 layers and six materials. The microfailure modes such as fiber breakage, fiber folding, layer (ply) failure, layer folding, and interlaminar delamination were predicted by principal strain of the anulus layer.
  
  
  RESULTS
  Excessively high tensile principal strain in the transverse direction of the anulus layer, indicating layer failure, was predicted in the anterior outer anulus. The strain level was much higher in the young model than in the old model. Compressive principal strain in the transverse direction of the anulus layer, predicting layer folding, was found in the posterior and posterolateral anulus.
  
  
  CONCLUSIONS
  Layer failure in the anterior outer anulus could occur in the early stage of life during extension with preload. This could then progress to formation of peripheral tears oriented at right angles to the fiber's direction.
authors.affiliation: ykimB@hotmail.com
authors.forename: Y
authors.initials: Y
authors.lastname: Kim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging; D003198:Computer Simulation; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000293:injuries* / Q000473:pathology; D008159:Lumbar Vertebrae / Q000293:injuries* / Q000473:pathology; D008875:Middle Aged; D008954:Models, Biological; D013122:Spinal Diseases / Q000209:etiology* / Q000473:pathology; D013314:Stress, Mechanical; D013718:Tensile Strength