Rheumatoid arthritis as a risk factor for a narrow C-2 pedicle: 3D analysis of the C-2 pedicle screw trajectory

Object. Vertebral artery (VA) injury is a potentially serious complication of C-2 pedicle screw (PS) fixation. Although this surgery is frequently performed in patients with rheumatoid arthritis (RA), few studies have compared the risk of VA injury in patients with and without RA. In this study, the authors compare the morphological risk of VA injury relating to C-2 PS fixation in patients with and without RA. Methods. A total of 110 3D CT images of the cervical spine including the axis were evaluated. Fifty patients with RA and 60 patients without RA were included in the study. The maximum PS diameter (MPSD) that could be used at C-2 without breaching the cortex was measured in 3D using a computer-assisted navigation system. A narrow-pedicle carrier was defined as a patient with an MPSD of 4 mm or less. Results. In the RA group, 42 of 100 MPSDs were <= 4 mm, and 30 of 50 patients (60%) were narrow-pedicle carriers. In the non-RA group, 10 of 120 MPSDs (8%) were <= 4 mm, and 8 of 60 (13%) patients were narrow-pedicle carriers. The MPSD, the anteroposterior (AP) diameter of C-3, and the ratio of MPSD to the AP diameter of C-3 were significantly smaller in the RA group than in the non-RA group. Multiple logistic regression analysis showed that RA and narrow C-3 AP diameter were significant risk factors for a narrow-pedicle carrier. Conclusions. Rheumatoid arthritis is a significant risk factor for a narrow C-2 pedicle. When performing PS placement at C-2, particularly in patients with RA, thorough preoperative evaluation of the bone architecture is very important for avoiding inadvertent injury to the VA.