C1???C2 Pedicle Screw Fixation with Rigid Cantilever Beam Construct: Case Report and Technical Note

Abstract

In Reply: We appreciate the comments of Dr. Goel about our article (9). Although it is true that screw fixation of the atlas and axis have been described previously by Dr. Goel and others, at the time of we submitted our technical note manuscript for publication, the use of rigid fixation had not been described. We do regret missing the references that Dr. Goel cites, although, to be fair, one of the references cited is a letter to the editor (2), one is a chapter that is not cited in MEDLINE (3), one is published in India and is not available on-line or in either of our institutions’ libraries (6), and one is a case report that was published in a non-peer-reviewed journal (5). We should have referenced and discussed Dr. Goel’s 1994 report of 30 cases of atlantoaxial dislocation treated with a posterior plate-screw system with no morbidity, mortality, or instrumentation failure and a 100% fusion rate (4). The main point of our technical note, however, was the ability to fixate the C1–C2 joint rigidly with a non-transarticular screw technique. The important difference between Dr. Goel’s technique and the one described in our technical note (and contemporaneously by Harms [8] and Stokes [10]) is the use of a rigid fixation system. The use of such a system provides a significant biomechanical advantage in terms of restricting both translation and rotation as compared with a nonfixed screw plate system such as that described by Dr. Goel. Although we are unaware of a biomechanical evaluation of Dr. Goel’s technique, we hypothesize that the mechanics would be similar or slightly superior to those of a Brooks-type C1–C2 fixation. In contrast, the mechanics of the rigid C1–C2 screw fixation were studied and presented in abstract form by Harms et al. (North American Spine Society, 2001) and Lynch et al. (AANS, 2002). Both of these groups of investigators found that fixation of C1 and C2 with a rigid screw-rod connector resulted in rigidity and strength comparable to that afforded by C1–C2 transarticular screw fixation. This increased rigidity is clinically relevant because, as seen with regard to C1–C2 transarticular screw fixation, it allows for higher fusion rates without the need for halo immobilization (1, 7). We agree with Dr. Goel’s statement that sectioning of the C2 root provides better visualization of the axis and allows for the placement of bone graft into the C1–C2 joint space without significant morbidity. We do not agree with the statement that sectioning of the root allows for the safe placement of the C2 screws under direct visualization, because the vertebral artery is still hidden. We recommend detailed preoperative imaging of the bony anatomy of C2 and the use of frameless stereotactic techniques when possible to decrease the risk of vertebral artery injury. Daniel K. Resnick Edward C. Benzel