Treating C1-2 subluxation with transarticular screw and posterior atlantoaxial fusion-A 5-year experience

Purpose: Since the introduction of C1-2 transarticular screw fixation by Magerl and Seemann in 1979, the technique has been used effectively in the treatment of atlantoaxial instability. In this study, a 5-year experience of using the technique of C1-2 transarticular screw fixation and posterior atlantoaxial fusion for atlantoaxial instability in 11 operations was reviewed. Materials and methods: From 2003 to 2007, 11 patients with atlantoaxial instability, with a mean age of 57 years, were included in the study. All patients underwent C1-2 stabilization with transarticular screw fixation and posterior atlantoaxial fusion. Preoperatively, every patient received a computed tomographic (CT) scan of the C2 level to determine the trajectory of screw placement and anatomic variations. Postoperatively, all patients were maintained in a hard neck collar for 6 weeks, and no halo fixation was used in any patient. A visual analog scale (VAS) was used for treatment assessment. Results: The mean isthmus heights for male and female patients were 8.08 ± 0.93 mm and 5.20 ± 1.45 mm, respectively, and the mean isthmus widths were 7.01 ± 0.98 mm and 4.54 ± 1.40 mm, showing significant difference (p < 0.05). Three female patients had an isthmus width less than 3 mm, and two had an isthmus height less than 4 mm due to high riding of vertebral artery. No significant difference between the sizes of right and left C2 isthmus was noted in this study. The average trajectory angle was 47.18 ± 5.27° caudo-cephalically and 4.85 ± 3.46° medially for males, and 38.30 ± 4.80° caudo-cephalically and 4.14 ± 1.67° medially for females. According to the results of the CT scan, three patients underwent unilateral screw fixation due to small isthmus size and risk of vertebral artery injury. Osseous fusion after surgical treatment, had been documented in 10 patients. The mean follow-up period was 2.6 years (range 22 months ∼ 4.5 years). The mean VAS was 7.55 ± 0.82 preoperatively and 1.81 ± 1.17 at 1 year after the operation (p < 0.05). There were no instances of screws loosening, superficial wound infection, errant screw placement, dural laceration, or operation-related neurovascular injury in this study. Conclusion: This study provides bone data of the C2 isthmus. C1-2 transarticular screw fixation with posterior atlantoaxial fusion provides stable fixation and a high fusion rate. Preoperatively, a CT scan is essential to recognize the location of a large vertebral foramen and narrow isthmus to avoid the risk of vertebral artery injury.