Applied anatomy of a minimally invasive muscle-splitting approach to posterior C1-C2 fusion: an anatomical feasibility study.

PURPOSE: To describe the applied anatomy of a minimally invasive muscle-splitting approach used to reach the posterior aspect of the C1-C2 complex. Atlantoaxial fusion using a midline posterior approach and polyaxial screw and rod system is widely used. Although minimally invasive variations of this technique have been recently reported, the complex applied anatomy of these approaches has not been described. The C1-C2 complex represents an unique challenge because of its bony and vascular anatomy. In this study, the applied anatomy and feasibility of this technique are examined on cadavers.
METHODS: The microsurgical anatomy of the upper cervical spine is examined on a formalin-fixed and on a fresh cadaver. The muscle-splitting approach is performed on 12 fresh cadavers using this technique.
RESULTS: The minimally invasive muscle-splitting approach is described in detail. Relevant anatomy and bony landmarks that aid screw placement in C1 and C2 could be well visualized. Using this approach, we were able to reach the lateral mass of the atlas and the inferior articular process and pars interarticularis of the axis in all of the nine cadavers. We placed mini polyaxial screws in C1 lateral mass and C2 pars interarticularis in four cadavers according to the technique described by Harms and Melcher.
CONCLUSIONS: Using this approach, it was possible to reach the posterior aspect of C1 and C2; the relevant anatomy needed to perform a C1-C2 fusion could be well visualized.