In vitro biomechanical evaluation of four fixation techniques for distractive–flexion injury stage 3 of the cervical spine

Abstract

Purpose. Anterior plate fixation has been reported to provide satisfactory results in cervical spine distractive flexion (DF) injuries stages 1 and 2, but will result in a substantial failure rate in more unstable stage 3 and above. The aim of this investigation was to determine the biomechanical properties of different fixation techniques in a DF-3 injury model where all structures responsible for the posterior tension band mechanism are torn.

Methods. The multidirectional three-dimensional stiffness of the subaxial cervical spine was measured in eight cadaveric specimens with a simulated DF-3 injury at C5–C6, stabilized with four different fixation techniques: anterior plate alone, anterior plate combined with posterior wire, transarticular facet screws, and a pedicle screw–rod construct, respectively.

Results. The anterior plate alone did not improve stability compared to the intact spine condition, thus allowing considerable range of motion around all three cardinal axes (p > 0.05). The anterior plate combined with posterior wire technique improved flexion–extension stiffness (p = 0.023), but not in axial rotation and lateral bending. When the anterior plate was combined with transarticular facet screws or with a pedicle screws–rod instrumentation, the stability improved in flexion–extension, lateral bending, and in axial rotation (p < 0.05).

Conclusions. These findings imply that the use of anterior fixation alone is insufficient for fixation of the highly unstable DF-3 injury. In these situations, the use of anterior fixation combined with a competent posterior tension band reconstruction (e.g. transarticular screws or a posterior pedicle screws–rod device) improves segmental stability.

Key words:

• Biomechanical analysis
• cervical spine
• distractive–flexion injury
• internal fixation
• transarticular screws
• pedicle screws

Acknowledgements

Funding was provided by Orthopaedic Associates Research Foundation, Inc., Towson, Maryland, USA. Cervical spinal implants were provided by Anatomica AB, Göteborg, Sweden. The statistical analysis was performed by Lars Lindhagen, PhD, biostatistician at Uppsala Clinical Research Center, Uppsala, Sweden.

Declaration of interest: None of the authors has any conflict of interest with regard to the content of this article.