Author: Tejaswy Potluri

Publisher:

Published: 2010

Total Pages: 100

ISBN-13:

Injuries to the neck, or cervical region, are very severe types of injuries since there is a potential risk of damage to the spinal cord. Any neck injury can have devastating if not life threatening consequences. The upper cervical spine consists of three vertebrae: The occiput (C0), the atlas (C1) and the axis (C2). Stabilization of the atlanto-axial complex following a neck injury is a challenging procedure because of its complicated anatomy. Several stabilization techniques have been reported for C1-C2 fixation. These techniques include posterior wiring and bone graft, posterior transarticular screws or a combination. Fixation with transarticular screws has been the gold standard in effectively stabilizing the segment. However, the drawback of using the transarticular screws is that they have a potential risk of vertebral artery injury due to a high riding transverse foramen of C2 vertebra, screw malposition or fracture of the C1 lateral mass. 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 atlanto-axial 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 C2 Pedicle Screw or C1 Lateral Mass Screw and C2 Intralaminar Screw or C1-2 Sublaminar Wire. The purpose of this study is to compare the biomechanical stability of the three C1-C2 transarticular screw salvaging fixation techniques through in vitro testing and finite element modeling. An in vitro testing using nine cadaver specimens was done to compare the degree of stability afforded by the three salvaging fixation techniques at C1-C2 level. To compare the efficiency of bilateral instrumentation over unilateral case, unilateral transarticular screw was also investigated. A finite element model of the C0-C3 has been developed and applied to study as well as compare the effects of the three C1-C2 transarticular screw fixation techniques on the biomechanical behavior of the upper cervical spine. The intact model was validated by comparing with previously published experimental results as well as with the in vitro results. Finite element models representing the following combinations with C1-2 Transarticular Screw on one side and: 1) C1 Lateral Mass Screw and C2 Pedicle Screw (TS+C1LMS+C2PS) 2) C1 Lateral Mass Screw and C2 Intralaminar Screw (TS+C1LMS+C2ILS) 3) C1-2 Sublaminar Wire (TS+WIRE) on the other side were evaluated. Various parameters like range of motion, facet loading and implant stresses were evaluated. Results show that all the three bilateral fixation procedures significantly reduced motion in all the loading modes when compared to unilateral fixation. When the three bilateral techniques were compared, TS+C1LMS+C2PS and TS+C1LMS+C2ILS afforded same stability and instrumentation stresses in all the loading modes. In addition, both the techniques were highly stable in axial rotation mode when compared to TS+WIRE. TS+WIRE resulted in higher stresses when compared to the other two bilateral techniques in all the loading modes.