title: Biomechanical analysis of the intact and destabilized sheep cervical spine.
abstract: METHODS
  An in vitro investigation of the biomechanics of the intact and destabilized sheep cervical spine.
  
  
  OBJECTIVE
  To establish the primary and coupled behaviors of the sheep cervical spine, levels C2-C7.
  
  
  BACKGROUND
  Sheep spine models are often used as a precursor to human cadaveric and clinical trials. Several studies have focused on the sheep anatomy and functional spinal unit biomechanics. However, there has not been a comprehensive study of the multilevel sheep cervical spine.
  
  
  METHODS
  Adult sheep cervical spines (C2-C7) were tested in flexion-extension, lateral bending, and axial rotation, using a 6-df testing apparatus. Moment-rotation curves were generated to understand the entire loading curve. Functional spinal units were tested at various levels of destabilization by sequentially removing the stabilizing structures (i.e., ligaments, facets).
  
  
  RESULTS
  The range of motion increased with caudal progression. The average total range of motion was approximately 77°, 130°, and 64° for flexion-extension, lateral bending, and axial rotation, respectively. The neutral zone accounted for a large range of motion during flexion-extension (~63%) and lateral bending (~72%). The flexion, extension, and axial rotation motion greatly increased after the removal of the capsular ligaments and facets. The C2-C3 has the largest change in motion during the various stages of destabilization.
  
  
  CONCLUSIONS
  The sheep cervical spine is extremely flexible, as seen by the large range of motion and neutral zone. The large neutral zone may account for the coupled motion between axial rotation and lateral bending. The facets and capsular ligaments provide significant stability, especially in axial rotation, flexion, and extension.
authors.affiliation: Department of Biomedical Engineering, The University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: DeVries
authors.forename: Anup A
authors.initials: AA
authors.lastname: Gandhi
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Fredericks
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Grosland
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Smucker
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000503:physiopathology* / Q000601:surgery; D004195:Disease Models, Animal; D007593:Joint Instability / Q000209:etiology / Q000503:physiopathology*; D016059:Range of Motion, Articular; D012399:Rotation; D012756:Sheep; D016474:Weight-Bearing