title: Rat disc torsional mechanics: effect of lumbar and caudal levels and axial compression load.
abstract: BACKGROUND
  Rat models with altered loading are used to study disc degeneration and mechano-transduction. Given the prominent role of mechanics in disc function and degeneration, it is critical to measure mechanical behavior to evaluate changes after model interventions. Axial compression mechanics of the rat disc are representative of the human disc when normalized by geometry, and differences between the lumbar and caudal disc have been quantified in axial compression. No study has quantified rat disc torsional mechanics.
  
  
  OBJECTIVE
  Compare the torsional mechanical behavior of rat lumbar and caudal discs, determine the contribution of combined axial load on torsional mechanics, and compare the torsional properties of rat discs to human lumbar discs.
  
  
  METHODS
  Cadaveric biomechanical study.
  
  
  METHODS
  Cyclic torsion without compressive load followed by cyclic torsion with a fixed compressive load was applied to rat lumbar and caudal disc levels.
  
  
  RESULTS
  The apparent torsional modulus was higher in the lumbar region than in the caudal region: 0.081+/-0.026 (MPa/degrees, mean+/-SD) for lumbar axially loaded; 0.066+/-0.028 for caudal axially loaded; 0.091+/-0.033 for lumbar in pure torsion; and 0.056+/-0.035 for caudal in pure torsion. These values were similar to human disc properties reported in the literature ranging from 0.024 to 0.21 MPa/degrees.
  
  
  CONCLUSIONS
  Use of the caudal disc as a model may be appropriate if the mechanical focus is within the linear region of the loading regime. These results provide support for use of this animal model in basic science studies with respect to torsional mechanics.
authors.affiliation: University of Pennsylvania, Philadelphia, PA 19104-6081, USA.
authors.forename: Alejandro A
authors.initials: AA
authors.lastname: Espinoza Orías
authors.forename: Neil R
authors.initials: NR
authors.lastname: Malhotra
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Elliott
mesh_terms: D000818:Animals; D002102:Cadaver; D019245:Compressive Strength / Q000502:physiology*; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D008159:Lumbar Vertebrae; D008297:Male; D019563:Mechanics; D023421:Models, Animal; D016059:Range of Motion, Articular / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013314:Stress, Mechanical