title: Biomechanical analysis comparing three C1-C2 transarticular screw salvaging fixation techniques.
abstract: METHODS
  This is an in vitro biomechanical study.
  
  
  OBJECTIVE
  To compare the biomechanical stability of the 3 C1-C2 transarticular screw salvaging fixation techniques.
  
  
  BACKGROUND
  Stabilization of the atlantoaxial complex is a challenging procedure because of its complicated anatomy. Many posterior stabilization techniques of the atlantoaxial complex have been developed with C1-C2 transarticular screw fixation been the current gold standard. The drawback of using the transarticular screws is that it has a potential risk of vertebral artery injury due to a high riding transverse foramen of C2 vertebra, and screw malposition. In such cases, it is not recommended to proceed with inserting the contralateral transarticular screw and the surgeon should find an alternative to fix the contralateral side. Many studies are available comparing different atlantoaxial stabilization techniques, but none of them compared the techniques to fix the contralateral side while using the transarticular screw on one side. The current options are C1 lateral mass screw and short C2 pedicle screw or C1 lateral mass screw and C2 intralaminar screw, or C1-C2 sublaminar wire.
  
  
  METHODS
  Nine fresh human cervical spines with intact ligaments (C0-C4) were subjected to pure moments in the 6 loading directions. The resulting spatial orientations of the vertebrae were recorded using an Optotrak 3-dimensional Motion Measurement System. Measurements were made sequentially for the intact spine after creating type II odontoid fracture and after stabilization with unilateral transarticular screw placement across C1-C2 (TS) supplemented with 1 of the 3 transarticular salvaging techniques on the contralateral side; C1 lateral mass screw and C2 pedicle screw (TS+C1LMS+C2PS), C1 lateral mass and C2 intralaminar screw (TS+C1LMS+C2ILS), or sublaminar wire (TS + wire).
  
  
  RESULTS
  The data indicated that all the 3 stabilization techniques significantly decreased motion when compared to intact in all the loading cases (left/right lateral bending, left/right axial rotation, flexion) except extension. All the 3 instrumented specimens were equally stable in extension/flexion and lateral bending modes. TS+C1LMS+C2PS was equivalent to TS+C1LMS+C2ILS (P > 0.05) and superior to TS + wire in axial rotation (P < 0.05). Also, TS+C1LMS+C2ILS was superior to TS + wire in axial rotation (P < 0.05).
  
  
  CONCLUSIONS
  Fixation of atlantoaxial complex using unilateral transarticular screw supplemented with contralateral C1 lateral mass and C2 intralaminar screws is biomechanically equivalent to C1 lateral mass and C2 pedicle screws and both are biomechanically superior to C1-C2 sublaminar wire in axial rotation.
authors.affiliation: Engineering Center for Orthopaedic Research Excellence, Department of Bioengineering, College of Engineering, University of Toledo, Toledo, OH, USA. helgafy@u.washington.edu
authors.forename: Hossein
authors.initials: H
authors.lastname: Elgafy
authors.forename: Tejaswy
authors.initials: T
authors.lastname: Potluri
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Goel
authors.forename: Scott
authors.initials: S
authors.lastname: Foster
authors.forename: Ahmad
authors.initials: A
authors.lastname: Faizan
authors.forename: Nikhil
authors.initials: N
authors.lastname: Kulkarni
mesh_terms: D001268:Atlanto-Axial Joint / Q000503:physiopathology / Q000601:surgery*; D001696:Biomechanical Phenomena; D001863:Bone Screws; D001864:Bone Wires; D002574:Cervical Vertebrae / Q000293:injuries / Q000503:physiopathology / Q000601:surgery*; D005592:Fracture Fixation / Q000295:instrumentation* / Q000379:methods*; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology / Q000517:prevention & control*; D016059:Range of Motion, Articular; D013314:Stress, Mechanical