title: Peak stresses observed in the posterior lateral anulus.
abstract: METHODS
  The stress distributions within cadaveric lumbar intervertebral discs were measured for a range of loading conditions.
  
  
  OBJECTIVE
  To examine the distribution of stress across the area of the intervertebral disc and to compare regional variations in peak stress during compression loading with various flexion angles.
  
  
  BACKGROUND
  The rate of disc degeneration and the occurrence of low back disorders increase with higher mechanical loading of the spine. The largest peak stresses occur in the anulus.
  
  
  METHODS
  Human lumbar L2--L3 and L4--L5 cadaver functional spinal units were obtained and tested. The distribution of disc stress was measured using a pressure probe with loads applied, pure compression and compression with 5 degrees of either flexion or extension.
  
  
  RESULTS
  Stress profiles were recorded across the intervertebral disc at a compressive force of 1000 N and each of the three flexion-extension angles. The highest values (2.99 +/- 1.31 MPa) were measured during extension-compression lateral to the midline of the disc in the posterior anulus. The pressure in the nucleus was relatively unchanged by flexion angle remaining about 1.00 MPa for a 1000-N compression.
  
  
  CONCLUSIONS
  Pressure measurements of the cadaveric nucleus have been used to validate models of lumbar spine loading and to evaluate the risk of low back injury and disc herniation. Previous observations limited to midsagittal measurements of the nucleus did not identify the regions of highest stress. The highest values observed here within the posterolateral anulus correspond to common sites of disc degeneration and herniation.
authors.affiliation: Department of Physical Medicine and Rehabilitation, SUNY Upstate Medical University, Syracuse, NY 13210, USA. edwardst@mail.upstate.edu
authors.forename: W T
authors.initials: WT
authors.lastname: Edwards
authors.forename: N R
authors.initials: NR
authors.lastname: Ordway
authors.forename: Y
authors.initials: Y
authors.lastname: Zheng
authors.forename: G
authors.initials: G
authors.lastname: McCullen
authors.forename: Z
authors.initials: Z
authors.lastname: Han
authors.forename: H A
authors.initials: HA
authors.lastname: Yuan
mesh_terms: D000328:Adult; D000368:Aged; D019245:Compressive Strength / Q000502:physiology; D004548:Elasticity; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D008159:Lumbar Vertebrae / Q000502:physiology; D008297:Male; D008875:Middle Aged; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology