Comparison of screw malposition and vertebral artery injury of C2 pedicle and transarticular screws: meta-analysis and review of the literature.

Study Design: Literature review and meta-analysis. Objectives: To compare the incidence of screw malposition and vertebral artery injury (VAI) with transarticular screws (TAS) and C2 pedicle screws (C2PS) using meta-analysis techniques. Summary of Background Data: Posterior instrumentation for atlantoaxial fusions can be challenging and risky. Some centers report a higher incidence of VAI with the implantation of TAS compared with C2PS, whereas other data do not support this. Methods: Online databases were searched for English language articles between 1994 and April 2011 describing the clinical and radiographic outcomes after insertion of C2PS or TAS. Forty-one studies reporting on 3627 TAS and 33 studies describing 2979 C2PS met inclusion criteria for VAI or clinically significant misplacements (VAI, neurological deficits, or misplacements requiring surgical revision), and 36 studies reporting on 3280 TAS and 28 studies describing 2532 C2PS met inclusion criteria for radiographic misplacement outcomes. Results: All studies comprised class III evidence. VAI occurred in 26 of 3627 (0.72%) implanted TAS and in 10 of 2979 (0.34%) implanted C2PS (P = 0.01). Clinically significant misplacements occurred in 67 TAS (1.84%) and in 10 C2PS (0.34%; P < 0.0001). The point estimate of VAI for TAS was 1.68% [confidence interval (CI), 1.23%-2.29%] and was higher than C2PS (1.09%; CI, 0.73%-1.63%; P = 0.01). The point estimate of clinically significant screw malposition for TAS was 2.33% (CI, 1.61%-3.37%) and was higher than that of C2PS (1.15%; CI, 0.77%-1.70%; P < 0.001). Conclusions: With training, experience, and anatomic knowledge, both TAS and C2PS can be inserted accurately and safely. However, improper insertion and VAI can have catastrophic consequences. Our review identified a higher risk of VAI, neurological injury, and clinically significant malpositions with TAS compared with C2PS. These data provide preliminary support for the supposition that C2PS have a lower risk of morbidity.