title: Biomechanical evaluation of five different occipito-atlanto-axial fixation techniques.
abstract: METHODS
  The stabilizing effects of five different occipitocervical fixations were compared.
  
  
  OBJECTIVE
  To evaluate the construct stability provided by five different occipito-atlanto-axial fixation techniques.
  
  
  BACKGROUND
  Few studies have addressed occipitocervical reconstruction stability and no studies to data have investigated anterior-posterior translational stiffness.
  
  
  METHODS
  A total of 21 human cadaveric spines were used. After testing intact spines (CO-C2), a type II dens fracture was created and five different reconstructions were performed: 1) occipital and sublaminar wiring/rectangular rod, 2) occipital screws and C2 lamina claw hooks/rod, 3) occipital screws, foramen magnum screws, and C1-C2 transarticular screws/rod, 4) occipital screws and C1-C2 transarticular screws/Y-plate, and 5) occipital screws and C2 pedicle screws/rod. Biomechanical testing parameters included axial rotation, flexion/extension, lateral bending, and anterior-posterior translation.
  
  
  RESULTS
  Pedicle screw fixation demonstrated the highest stiffness among the five reconstructions (P < 0.05). The two types of transarticular screw methods provided greater stability than hook or wiring reconstructions (P < 0.05). The C2 claw hook technique resulted in greater stability than sublaminar wiring fixation in anterior-posterior translation (P < 0.05). However, the wiring procedure did not significantly increase the stiffness levels beyond the intact condition under anterior-posterior translation and lateral bending (P > 0.05).
  
  
  CONCLUSIONS
  C2 transpedicular and C1-C2 transarticular screws significantly increased the stabilizing effect compared to sublaminar wiring and lamina hooks. The improved stability afforded by C2 pedicular and C1-C2 transarticular screws offer many potential advantages including a high rate of bony union, early ambulation, and easy nursing care.
  
  
  CONCLUSIONS
  Occipitocervical reconstruction techniques using C1-C2 transarticular screws or C2 pedicle screws offer biomechanical advantages compared to sublaminar wiring or lamina hooks. Pedicle screw fixation exhibited the highest construct stiffness among the five reconstructions.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Union Memorial Hospital, Baltimore, Maryland, USA. odaitr@aol.com
authors.forename: I
authors.initials: I
authors.lastname: Oda
authors.forename: K
authors.initials: K
authors.lastname: Abumi
authors.forename: L C
authors.initials: LC
authors.lastname: Sell
authors.forename: C J
authors.initials: CJ
authors.lastname: Haggerty
authors.forename: B W
authors.initials: BW
authors.lastname: Cunningham
authors.forename: P C
authors.initials: PC
authors.lastname: McAfee
mesh_terms: D000368:Aged; D001268:Atlanto-Axial Joint / Q000502:physiology / Q000601:surgery*; D001269:Atlanto-Occipital Joint / Q000502:physiology / Q000601:surgery*; D001696:Biomechanical Phenomena; D001858:Bone Nails; D001863:Bone Screws; D001864:Bone Wires; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*