title: Needle puncture in rabbit functional spinal units alters rotational biomechanics.
abstract: METHODS
  An in vitro biomechanical study for rabbit lumbar functional spinal units (FSUs) using a robot-based spine testing system.
  
  
  OBJECTIVE
  To elucidate the effect of annular puncture with a 16 G needle on mechanical properties in flexion/extension, axial rotation, and lateral bending.
  
  
  BACKGROUND
  Needle puncture of the intervertebral disk has been shown to alter mechanical properties of the disk in compression, torsion, and bending. The effect of needle puncture in FSUs, where intact spinal ligaments and facet joints may mitigate or amplify these changes in the disk, on spinal motion segment stability subject to physiological rotations remains unknown.
  
  
  METHODS
  Rabbit FSUs were tested using a robot testing system whose force/moment and position precision were assessed to demonstrate system capability. Flexibility testing methods were developed by load-to-failure testing in flexion/extension, axial rotation, and lateral bending. Subsequent testing methods were used to examine a 16 G needle disk puncture and No. 11 blade disk stab (positive control for mechanical disruption). Flexibility testing was used to assess segmental range-of-motion (degrees), neutral zone stiffness (N m/degrees) and width (degrees and N m), and elastic zone stiffness before and after annular injury.
  
  
  RESULTS
  The robot-based system was capable of performing flexibility testing on FSUs-mean precision of force/moment measurements and robot system movements were <3% and 1%, respectively, of moment-rotation target values. Flexibility moment targets were 0.3 N m for flexion and axial rotation and 0.15 N m for extension and lateral bending. Needle puncture caused significant (P<0.05) changes only in flexion/extension range-of-motion and neutral zone stiffness and width (N m) compared with preintervention. No. 11 blade-stab significantly increased range-of-motion in all motions, decreased neutral zone stiffness and width (N m) in flexion/extension, and increased elastic zone stiffness in flexion and lateral bending.
  
  
  CONCLUSIONS
  These findings suggest that disk puncture and stab can destabilize FSUs in primary rotations.
authors.affiliation: Departments of *Physical Medicine and Rehabilitation †Bioengineering ‡Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, PA §Finance and Trade Hospital of Hunan Province, Tianxin, Changsha ∥The First Affiliated Hospital of University of South China, Xiangtan, Hunan, China.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Hartman
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Bell
authors.forename: Bichun
authors.initials: B
authors.lastname: Quan
authors.forename: Yao
authors.initials: Y
authors.lastname: Nuzhao
authors.forename: Gwendolyn A
authors.initials: GA
authors.lastname: Sowa
authors.forename: James D
authors.initials: JD
authors.lastname: Kang
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D005260:Female; D066298:In Vitro Techniques; D007403:Intervertebral Disc / Q000502:physiology; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery*; D009339:Needles; D011677:Punctures; D011817:Rabbits; D016059:Range of Motion, Articular; D012399:Rotation; D021801:Zygapophyseal Joint / Q000502:physiology / Q000601:surgery