Usefulness of Unilateral Posterior Atlantoaxial Transarticular Screw Fixation in Patients with Atlantoaxial Instability: Comparison with Bilateral Method by 6-Month Follow-up

Abstract

PURPOSE : Bilateral C1-2 transarticular screw fixation with bone graft and wiring has been the best treatment for atlantoaxial instability. However, several factors may disturb satisfactory placement of bilateral screws. This study evaluates the safety and usefulness of unilateral screw placement when bilateral screw fixation is not available.

MATERIALS AND METHODS : Between January 2003 and December 2007, transarticular screw fixation was performed in 54 patients with atlantoaxial instability. Preoperative studies including cervical x-ray, three dimensional computed tomogram, vertebral angiogram, and magnetic resonance image were checked. The atlanto-dental interval (ADI) was measured and compared by traditional manner in preoperative period, immediate postoperatively, and postoperative 1, 3 and 6 months.

RESULTS : Unilateral transarticular screw fixation was performed with interspinous wiring in 27 patients (50%). The causes of unilateral screw fixation were anomalous course of vertebral artery in 20 patients (74%), severe degenerative arthritis in 3 (11%), fracture of C1 in 2 (7%), hemangioblastoma in one, and screw malposition in one, respectively. Postoperatively, the mean ADI in unilateral group was measured as 2.63mm in immediate postoperatively, 2.61mm in 1 month, 2.64mm in 3 months and 2.61mm in 6 months postoperatively. The mean ADI of bilateral group was also measured as following; 2.76mm in immediate postoperative, 2.71mm in 1 month, 2.73mm in 3 months, 2.73mm in 6 months postoperatively. Comparison of ADI measurement showed no significant difference in both groups, and moreover fusion rate was 100% in bilateral and 96.3% in unilateral group (p=0.317).

CONCLUSION : In biomechanical perspectives, bilateral transarticular screw fixation is best option for AAI, nevertheless unilateral screw fixation also can be a useful alternative in otherwise dangerous or infeasible cases through bilateral screw placement.