title: Biomechanical comparison of C1-2 posterior fixation techniques.
abstract: OBJECTIVE
  In a nondestructive, repeated-measures in vitro flexibility experiment, the authors compared the acute stability of C1-2 after placement of C-1 lateral mass and C-2 pars interarticularis (LC1-PC2) instrumentation with that of C1-2 transarticular screw fixation.
  
  
  METHODS
  The effect of C-1 laminectomy and C1-2 interspinous cable/graft fixation on LC1-PC2 stability was studied. Screw pullout strengths were also compared. Seven human cadaveric occiput-C3 specimens were loaded nondestructively with pure moments while measuring nonconstrained atlantoaxial motion. Specimens were tested with graft alone, LC1-PC2 alone, LC1-PC2 combined with C-1 laminectomy, and graft-augmented LC1-PC2. Interspinous cable/graft fixation significantly enhanced LC1-PC2 stability during extension. After C-1 laminectomy, the LC1-PC2 construct allowed increased motion during flexion and extension. There was no significant difference in lax zone or range of motion between LC1-PC2 fixation and transarticular screw fixation, but graft-assisted transarticular screws yielded a significantly smaller stiff zone during extension. The difference in pullout resistance between C-1 lateral mass screws and C-2 pars interarticularis screws was insignificant. The LC1-PC2 region restricted motion to within the normal range during all loading modes. Atlantal laminectomy reduced LC1-PC2 stability during flexion and extension.
  
  
  CONCLUSIONS
  The instrumentation-augmented LC1-PC2 construct performed biomechanically similarly to the C1-2 transarticular screw fixation. The LC1-PC2 construct resisted flexion, lateral bending, and axial rotation well. The weakness of the LC1-PC2 fixation in resisting extension can be overcome by adding an interspinous graft to the construct.
authors.affiliation: Division of Neurological Surgery and Spinal Biomechanics Research Laboratory, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, Phoenix, Arizona 85013, USA.
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Hott
authors.forename: James J
authors.initials: JJ
authors.lastname: Lynch
authors.forename: Robert H
authors.initials: RH
authors.lastname: Chamberlain
authors.forename: Volker K H
authors.initials: VK
authors.lastname: Sonntag
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
mesh_terms: D000328:Adult; D001268:Atlanto-Axial Joint / Q000503:physiopathology / Q000601:surgery*; D001696:Biomechanical Phenomena; D001863:Bone Screws; D016025:Bone Transplantation; D002574:Cervical Vertebrae / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D007593:Joint Instability / Q000503:physiopathology / Q000601:surgery*; D007796:Laminectomy / Q000295:instrumentation*; D008297:Male; D008875:Middle Aged; D010780:Photogrammetry; D018583:Pliability; D011183:Postoperative Complications / Q000503:physiopathology*; D013123:Spinal Fusion / Q000295:instrumentation*; D016474:Weight-Bearing / Q000502:physiology