THE ANATOMICAL SUITABILITY OF THE C1-2 COMPLEX FOR TRANSARTICULAR SCREW FIXATION

Posterior transarticular screw fixation of the C1-2 complex has become an accepted method of rigid internal fixation for patients requiring posterior C1-2 fusion. The principal limitation of this procedure is t he location of the vertebral artery, because an anomalous position may prohibit screw placement. Ln this study, a consecutive series of comp uterized tomography (CT) scans was reviewed, and the suitability of ea ch patient for transarticular screw fixation was evaluated. All of the fine-slice axial C1-2 CT scans and reconstructions performed on a spi ral scanner over 2 years were reviewed. A novel screw trajectory recon struction was designed to visualize the potential path of a transartic ular screw in the plane of the reconstruction. Scans were reviewed for bone anatomy and the position of the transverse foramen. Seventeen (1 8%) of 94 patients had a high-riding transverse foramen on at least on e side of the C-2 vertebra that would prohibit the placement of transa rticular screws. The left side was involved in nine patients and the r ight in five. Three patients had bilateral anomalies. The mean age of the group with anomalies (35.9 years, range 10-76) was not significant ly different from the overall mean age (35.7 years, range 6-94). An ad ditional five patients (5%) were considered to have anatomy in which s crew placement was feasible but risky. On the basis of these data, it is postulated that 18% to 23% of patients may not be suitable candidat es for posterior C1-2 transarticular screw fixation on at least one si de.