A technique for frameless stereotaxy and placement of transarticular screws for atlanto-axial instability in rheumatoid arthritis

The aim of the present study was to outline a new surgical technique and de scribe how, in a clinical setting, computer-generated image-guidance can as sist in the planning and accurate placement of transarticular C1/C2 screws inserted using a minimally invasive exposure. Forty-six patients with atlan to-axial instability due to rheumatoid arthritis underwent posterior stabil isation with transarticular screws. This was achieved with a minimal poster ior exposure limited to C1 and C2 and percutaneous screw insertions via min or stab incisions. The Stealth Station (Medtronic Sofamor Danek, Memphis, T enn., USA) was used for image guidance to navigate safely through C2. Recon structed computed tomographic (CT) scans of the atlanto-axial complex were used for image guidance. It was possible to perform preoperative planning o f the screw trajectory taking into account the position of the intraosseous portion of the vertebral arteries, the size of the pars interarticularis a nd the quality of bone in C2. Screws could be inserted percutaneously over K-wires using a drill guide linked to the image-guidance system. Preoperati ve planning was performed in all 46 patients and accurate registration allo wed proposed screw trajectories to be identified. Thirty-eight patients had bilateral screws inserted and eight had a unilateral screw. A total of 84 screws were inserted using the Stealth Station. There were no neurovascular injuries. This technique for placing transarticular screws is accurate and safe. It allows a minimally invasive approach to be followed. Image guidan ce is a useful adjunct for the surgeon undertaking complex spinal procedure s.