title: The multidirectional bending properties of the human lumbar intervertebral disc.
abstract: BACKGROUND
  While the biomechanical properties of the isolated intervertebral disc have been well studied in the three principal anatomic directions of flexion/extension, axial rotation, and lateral bending, there is little data on the properties in the more functional directions that are combinations of these principal anatomic directions.
  
  
  OBJECTIVE
  To determine the bending flexibility, range of motion (ROM), and neutral zone (NZ) of the human lumbar disc in multiple directions and to determine if the values about the combined moment axes can be predicted from the values about principal moment axes.
  
  
  METHODS
  Three-dimensional biomechanical analysis of the elastic bending properties of human lumbar discs about principal and combined moment axes.
  
  
  METHODS
  Pure, unconstrained moments were applied about multiple axes. The bending properties (flexibility, ROM, and NZ) of isolated lumbar discs (n=4 for L2/L3 and n=3 for L4/L5) were determined in the six principal directions and in 20 combined directions. The experimental values were compared with those predicted from the linear combination of the six principal moment axes.
  
  
  RESULTS
  The maximum and minimum values of the biomechanical properties were found at the principal moment axes. Among combined moment axes, ROM and NZ (but not flexibility) values were predicted from the principal moment axis values.
  
  
  CONCLUSIONS
  The principal moment axes coincide with the primary mechanical axes of the intervertebral disc and demonstrate significant differences in direction for values of flexibility, ROM, and NZ. Not all combined moment axis values can be predicted from principal moment axis values.
authors.affiliation: Department of Orthopaedics, Brown Medical School/Rhode Island Hospital, Providence, RI 02903, USA.
authors.forename: David
authors.initials: D
authors.lastname: Spenciner
authors.forename: David
authors.initials: D
authors.lastname: Greene
authors.forename: James
authors.initials: J
authors.lastname: Paiva
authors.forename: Mark
authors.initials: M
authors.lastname: Palumbo
authors.forename: Joseph
authors.initials: J
authors.lastname: Crisco
mesh_terms: D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D008159:Lumbar Vertebrae / Q000502:physiology*; D008875:Middle Aged; D018583:Pliability; D016059:Range of Motion, Articular