title: Immediate biomechanical effects of lumbar posterior dynamic stabilization above a circumferential fusion.
abstract: METHODS
  Biomechanical in vitro human cadaveric lumbar flexibility testing with 6 sequential treatments.
  
  
  OBJECTIVE
  To compare the range of motion (ROM) of dynamic one-level posterior stabilization constructs to one-level rigid rod fixation constructs and to study the effects of extending the posterior construct to the adjacent superior level.
  
  
  BACKGROUND
  Patients experiencing pain and biomechanical instability at one level may also present with radiographic or other indicators of early degeneration at an adjacent level. Clearly, fusion would be warranted at the symptomatic level, but the treatment plan for the adjacent level remains controversial. Additionally, the effects on adjacent motion segments above a fusion level are currently not well understood.
  
  
  METHODS
  Thirteen fresh frozen human cadaveric lumbar spines (L1-L5) were tested in 6 modes of loading: 3 were randomized to dynamic posterior stabilization constructs and 7 to a rigid rod pedicle screw system. Each group was subjected to 6 treatments.
  
  
  RESULTS
  When comparing the instrumented treatments, only Treatment 6, two-level hybrid constructs, exhibited a statistically significant effect in flexion-extension bending at L2-L3 between the posterior dynamic system and rigid rod fixation (P = 0.014).
  
  
  CONCLUSIONS
  ROM at the superior adjacent level (L2-L3) demonstrated no significant difference between intact, destabilized, one-level posterior fixation, and one-level circumferential fusion at the index level (L3-L4) when comparing posterior dynamic stabilization to rigid rod fixation. However, ROM at the superior adjacent level (L2-L3) was significantly greater for lateral bending and axial rotation when both levels (L2-L3 and L3-L4) were stabilized with a dynamic stabilization system. When the functional spinal units were instrumented with a two-level hybrid construct, two-level posterior instrumentation (L2-L3 and L3-L4) with a cage at the index level (L3-L4), all bending modes generated significantly greater ROM for the dynamic stabilization group at L2-L3 compared with rigid rod fixation.
authors.affiliation: Department of Neurological Surgery, University of Pittsburgh, Pittsburgh, PA, USA. chengb@upmc.edu
authors.forename: Boyle C
authors.initials: BC
authors.lastname: Cheng
authors.forename: Jeff
authors.initials: J
authors.lastname: Gordon
authors.forename: Joseph
authors.initials: J
authors.lastname: Cheng
authors.forename: William C
authors.initials: WC
authors.lastname: Welch
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D006801:Humans; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000503:physiopathology / Q000601:surgery*; D011897:Random Allocation; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods