Biomechanical evaluation of transfacet screw fixation for stabilization of multilevel cervical corpectomies.

ABSTRACT

STUDY DESIGN: Cadaveric biomechanical investigation. OBJECTIVES: To test the feasibility of transfacet screws as a minimally invasive posterior fixation device for the cervical spine by comparing the biomechanical stability of transfacet screws to lateral mass screws and rods in a multilevel cervical corpectomy model. SUMMARY OF BACKGROUND DATA Minimally invasive surgery (MIS) of the spine has gained increasing acceptance and popularity. However, a minimally invasive means of instrumenting the posterior cervical spine has yet to be discovered. Posterior transfacet screws have been described as a means of posterior fixation. In addition, they have the potential of being placed percutaneously through stab incisions. However, validation of transfacet screws in an unstable cervical model in which posterior instrumentation may be necessary has not been carried out till date. METHODS: Sixteen cadaveric cervical spines were randomized to transfacet or lateral mass instrumentation groups. The spines were tested in the following conditions (a) intact, (b) after multilevel corpectomies with strut graft placement with stand-alone posterior fixation, and (c) with an additional anterior plate over the strut graft. Corpectomy site loading was measured with a custom-designed strut graft. Data were collected for spinal stiffness, range of motion, and strut graft loading, and was analyzed using 2-way analysis of variance (P<0.05). RESULTS: Stand-alone transfacet screw fixation was found to provide inferior spinal stability and resulted in increased spinal motion and graft loading compared with the other constructs (P<0.05 for all). CONCLUSIONS: It is unclear what kind of mechanical stiffness is necessary to stabilize the cervical spine and obtain solid fusion. However, decreased stability and increased graft loading suggest that transfacet screws may not be the ideal method of posterior fixation to supplement multilevel anterior cervical corpectomies and fusions despite their potential as a minimally invasive method for posterior cervical instrumentation.