title: An in vitro model of degenerative lumbar spondylolisthesis.
abstract: METHODS
  A biomechanical human cadaveric study.
  
  
  OBJECTIVE
  To create a biomechanical model of low-grade degenerative lumbar spondylolisthesis (DLS), defined by anterior listhesis, for future testing of spinal instrumentation.
  
  
  BACKGROUND
  Current spinal implants are used to treat a multitude of conditions that range from herniated discs to degenerative diseases. The optimal stiffness of these instrumentation systems for each specific spinal condition is unknown. Ex vivo models representing degenerative spinal conditions are scarce in the literature. A model of DLS for implant testing will enhance our understanding of implant-spine behavior for specific populations of patients.
  
  
  METHODS
  Four incremental surgical destabilizations were performed on 8 lumbar functional spinal units. The facet complex and intervertebral disc were targeted to represent the tissue changes associated with DLS. After each destabilization, the specimen was tested with: (1) applied shear force (-50 to 250 N) with a constant axial compression force (300 N) and (2) applied pure moments in flexion-extension, lateral bending and axial rotation (±5 Nm). Relative motion between the 2 vertebrae was tracked with a motion capture system. The effect of specimen condition on intervertebral motion was assessed for shear and flexibility testing.
  
  
  RESULTS
  Shear translation increased, specimen stiffness decreased and range of motion increased with specimen destabilization (P < 0.0002). A mean anterior translation of 3.1 mm (SD 1.1 mm) was achieved only after destabilization of both the facet complex and disc. Of the 5 specimen conditions, 3 were required to achieve grade 1 DLS: (1) intact, (3) a 4-mm facet gap, and (5) a combined nucleus and annulus injury.
  
  
  CONCLUSIONS
  Destabilization of both the facet complex and disc was required to achieve anterior listhesis of 3.1 mm consistent with a grade 1 DLS under an applied shear force of 250 N. Sufficient listhesis was measured without radical specimen resection. Important anatomical structures for supporting spinal instrumentation were preserved such that this model can be used in future to characterize behavior of novel instrumentation prior to clinical trials.
authors.affiliation: Department of Orthopaedics,International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Angela D
authors.initials: AD
authors.lastname: Melnyk
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Kingwell
authors.forename: Qingan
authors.initials: Q
authors.lastname: Zhu
authors.forename: Jason D
authors.initials: JD
authors.lastname: Chak
authors.forename: Peter A
authors.initials: PA
authors.lastname: Cripton
authors.forename: Charles G
authors.initials: CG
authors.lastname: Fisher
authors.forename: Marcel F
authors.initials: MF
authors.lastname: Dvorak
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Oxland
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology / Q000601:surgery; D008159:Lumbar Vertebrae / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D018583:Pliability; D019736:Prostheses and Implants; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D013168:Spondylolisthesis / Q000503:physiopathology* / Q000601:surgery; D021801:Zygapophyseal Joint / Q000503:physiopathology / Q000601:surgery