Stabilization of the C1-C2 articulation.

When assessing a new technique or a modification of an existing one, surgeons very rarely have the luxury of high level randomized prospective studies on which to base their decisions. This is certainly the case when considering the surgical options for stabilization of the C1-2 articulation.

Because of this we must therefore make our decisions by evaluating the clinical situation, mechanical and anatomic factors, and the collected reports of those who are experienced and willing to discuss their experience. As Dr. Fountas and his colleagues point out in this issue of the Journal (1), there are a number of reasons for people to develop instability at this level, with trauma and inflammatory processes being the most common. Because of the potentially grave consequences if left untreated, surgical stabilization is generally recommended once clear instability has been shown, with the exception being in the case of acute fracture that still has the potential to heal with nonoperative treatment.

Transarticular screw fixation has an undisputed mechanical advantage over wiring and clamp techniques. It is similar in strength to a technique which involves placement of a screw into the pars of C2, another into the inferior aspect of the lateral mass of C1, and connection of the two with a rod. The advantage of these screw techniques is that the increased rigidity allows for less postoperative immobilization, and probably provides a better environment for eventual bony fusion.

The difficult aspect for many of us who do this surgery is the anatomy. Before the introduction of this technique, the variable intra osseous course of the vertebral artery within C2 was of little surgical importance because surgeons rarely ventured there. Now I believe it is what causes the greatest anxiety. The greatest concern with wiring and clamping techniques was actually the spinal cord, as these procedures were done under the lamina of C1 and/or C2. Although injury to the spinal cord is not impossible with the screw techniques, there is probably less risk because screw fixation is performed more laterally. Other anatomic structures that need to be accounted for with this technique are: the nerve root of C2, which does not have the typical bony protection given to other nerve roots as they exit the spinal canal; the atlanto-occipital articulation, which can be violated if the screw is directed too far cranially; and the structures that are anterior to this articulation, particularly the internal carotid artery which can lie on the anterior surface of C1.

Given the mechanical advantages but worrisome anatomy involved with this procedure, the reported experience of surgeons like those who wrote this paper becomes very important. This report, along with others referenced in the paper, shows that with appropriate planning and surgical technique, the vertebral artery can (usually) be avoided. The rate of successful arthrodesis is high and the complication rate is acceptably low. Another point this paper illustrates is that fluoroscopic guidance works well, and high tech navigation systems are not mandatory.

Although the preponderance of literature regarding transarticular screw fixation is retrospective, this paper is part of an increasing body of evidence that the procedure is a reasonable one and can be incorporated into the practices of surgeons who operate in this area. This is not to say that other techniques, such as the Brooks and Gallie wiring techniques, need to be abandoned, but that screw fixation is another option for stabilization of the C1-2 complex.

Accepted April 7, 2004.

Please see "C1-C2 Transarticular Screw Fixation for Atlantoaxial Instability" on page 1042 of this issue.

Reference

1. Fountas KN, Kapsalaki EZ, Karampelas I, et al. C1-C2 transarticular screw fixation for atlantoaxial instability. South Med J 2004;97:1042-1048.

John Glaser, MD

From the Medical University of South Carolina Medical Center, Department of Orthopaedic Surgery, Charleston, SC.

Reprint requests to John Glaser, MD, Medical University of South Carolina Medical Center, Department of Orthopaedic Surgery, 96 Jonathan Lucas, Suite 708, Charleston, SC 29425. Email: [e-mail]