title: Bicortical facet screws as a new option for posterior C2 fixation: anatomical study and clinical experience.
abstract: C2 fixation is a demanding procedure, particularly in patients with variants of C1-C2 anatomy. The inferior articular process (IAP) of the axis can be an alternative for screw placement. We report the results of a CT study of C2 IAP anatomy and we present the clinical experience of 28 patients operated with this technique.
  
  
  
  Anatomical study: 50 CT angiographies of the vertebral arteries (VA) were used for this study and, therefore, 100 IAPs were considered. We measured on the axial and sagittal planes the length, height and width of the facet, the distance between the anterior cortex and the VA and the distance between the screw entry point and the VA. We also measured the angle between the sagittal plane and the external tangent line of the VA.
  
  
  
  28 patients were treated with C2 IAP screws at the Spine Surgery Department of the University Hospital in Lyon, France, from January 2014 to January 2016.
  
  
  
  Anatomical study: the mean length of C2 IAP was 12 ± 2 mm, the mean distance between the anterior cortical layer and the VA was 5.2 ± 1.4 mm, and the mean angle we found was 0.2° ± 5.3°.
  
  
  
  16 of the 28 patients presented post-traumatic C1-C2 instability, 8 patients presented degenerative disease, 1 patient was treated for pseudoarthrosis, 1 for tumour, 1 for OPLL and 1 for rheumatoid arthritis. All the screws were correctly positioned and there was no VA injury.
  
  
  
  IAP screws can represent a safe alternative option for C2 fixation.
authors.affiliation: Spine Surgery Department, Lyon University Hospital, 52 Boulevard Pinel, 69500, Bron, France. angelo.rusconi@hotmail.com.
authors.forename: Angelo
authors.identifier: 0000-0002-7553-837X
authors.initials: A
authors.lastname: Rusconi
authors.affiliation: Spine Surgery Department, Lyon University Hospital, 52 Boulevard Pinel, 69500, Bron, France.
authors.forename: E
authors.initials: E
authors.lastname: Freitas-Olim
authors.affiliation: Spine Surgery Department, Lyon University Hospital, 52 Boulevard Pinel, 69500, Bron, France.
authors.forename: P
authors.initials: P
authors.lastname: Coloma
authors.affiliation: Spine Surgery Department, Lyon University Hospital, 52 Boulevard Pinel, 69500, Bron, France.
authors.forename: R
authors.initials: R
authors.lastname: Messerer
authors.affiliation: Spine Surgery Department, Lyon University Hospital, 52 Boulevard Pinel, 69500, Bron, France.
authors.forename: C
authors.initials: C
authors.lastname: Barrey
mesh_terms: D001863:Bone Screws; D002574:Cervical Vertebrae / Q000601:surgery*; D000072226:Computed Tomography Angiography; D006801:Humans; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D014711:Vertebral Artery / Q000000981:diagnostic imaging
keywords: Atlanto-axial instability; Axis fixation; C1–C2 fixation; Cervical trauma; Occipito-cervical fusion