title: [Biomechanical evaluation of stiffness of long-segment instrumented spine].
abstract: OBJECTIVE
  To test the changes of the stiffness of the intact, released, and instrumented spines in an in vitro porcine model.
  
  
  METHODS
  Twelve porcine spines (12 segments each) were harvested for the biomechanical tests with Material Test System. Stiffness during flexion, extension, lateral bending, and axial rotation were recorded; then the specimen was released with intervertebral discs and the facet joints removed, followed by repeating the biomechanical tests for stiffness; and finally, a double-rod titanium construct was applied for internal fixation to each released spine and stiffness tests were repeated again.
  
  
  RESULTS
  Compared with the intact porcine spines [stiffness during flexion, extension, lateral bending, and axial rotation was 52.89 +/- 15.98, 105.43 +/- 56.38, 42.09 +/- 14.73, and (16.94 +/- 4.85) N x mm/degrees, respectively], the stiffness of the released porcine spines [stiffness during flexion, extension, lateral bending, and axial rotation was 44.04 +/- 13.73, 41.46 +/- 10.80, 31.75 +/- 7.23, and (9.10 +/- 2.07)N x mm/degrees, respectively] significantly decreased (P < 0.05), while significantly increased stiffness was found in the instrumented porcine spines [stiffness during flexion, extension, lateral bending, and axial rotation was 385.96 +/- 143.25, 138.96 +/- 59.41, 152.56 +/- 87.15, and (55.91 +/- 16.49) N x mm/degrees, respectively] (P < 0.05).
  
  
  CONCLUSIONS
  Higher instant stiffness was found in instrumented spine than the intact one during flexion, extension, lateral bending and axial rotation.
authors.affiliation: Department of Orthopaedics Surgery, PUMC Hospital, CAMS and PUMC, Beijing 100730, China. zhangjia@medmail.com.cn
authors.forename: Jia
authors.initials: J
authors.lastname: Zhang
authors.forename: William W
authors.initials: WW
authors.lastname: Lu
authors.forename: Qi-bin
authors.initials: QB
authors.lastname: Ye
authors.forename: Gui-xing
authors.initials: GX
authors.lastname: Qiu
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D017586:Diskectomy; D005593:Fracture Fixation, Internal; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000601:surgery; D016059:Range of Motion, Articular / Q000502:physiology*; D013123:Spinal Fusion / Q000379:methods; D013131:Spine / Q000601:surgery*; D013314:Stress, Mechanical; D013552:Swine; D013904:Thoracic Vertebrae / Q000601:surgery