title: Biomechanical comparison of five different atlantoaxial posterior fixation techniques.
abstract: METHODS
  Five different reconstructions of the atlantoaxial complex were biomechanically compared in vitro in a nondestructive test.
  
  
  OBJECTIVE
  To determine whether non-bone graft-dependent one-point fixation affords stability levels equivalent to three-point reconstructions.
  
  
  BACKGROUND
  Previous investigations have demonstrated that three-point fixation, using bilateral transarticular screws in combination with posterior wiring, provide the most effective resistance to minimize motion around C1-C2. However, placement of transarticular screws is technically demanding. Posterior wiring techniques affording one-point fixation have failure rates of approximately 15%, with failure considered to be secondary to structural bone graft failures. One-point, non-bone graft-dependent fixations have not been tested.
  
  
  METHODS
  Eight human cervical specimens, C0-C3 were loaded nondestructively. Unconstrained three-dimensional segmental motion was measured. The reconstructions tested were two one-point fixations, one two-point fixation, and two three-point fixations.
  
  
  RESULTS
  Under axial rotation two and three-point reconstructions provided better stiffness than the one-point reconstructions (P < 0.05). During flexion-extension, higher stiffness levels were observed in one- and three-point fixations when compared with the intact spine (P < 0.05). In lateral bending no significant differences were observed among the six groups, although the trend was that reconstructions including transarticular screws provided greater stability than one-point fixations.
  
  
  CONCLUSIONS
  The current findings substantiate the use of three-point fixation as the treatment of choice for C1-C2 instability. [l: atlantoaxial fixation, biomechanics, cervical spine, instability, spinal instrumentation, transarticular screws]
authors.affiliation: Department of Orthopaedics, Uppsala University Hospital, Uppsala, Sweden. thomas.henriques@beta.telenordia.se
authors.forename: T
authors.initials: T
authors.lastname: Henriques
authors.forename: B W
authors.initials: BW
authors.lastname: Cunningham
authors.forename: C
authors.initials: C
authors.lastname: Olerud
authors.forename: N
authors.initials: N
authors.lastname: Shimamoto
authors.forename: G A
authors.initials: GA
authors.lastname: Lee
authors.forename: S
authors.initials: S
authors.lastname: Larsson
authors.forename: P A
authors.initials: PA
authors.lastname: McAfee
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001268:Atlanto-Axial Joint / Q000502:physiology / Q000601:surgery*; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000502:physiology / Q000601:surgery*; D004548:Elasticity; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007593:Joint Instability / Q000601:surgery; D008297:Male; D018583:Pliability; D012399:Rotation; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D016474:Weight-Bearing / Q000502:physiology