Is rheumatoid arthritis a risk factor for a high-riding vertebral artery?

Study Design. A retrospective comparative study on the morphologic characteristics of the axis in patients with or without rheumatoid arthritis (RA). Objective. To compare the morphologic risk of vertebral artery (VA) injury during atlantoaxial transarticular screw fixation between patients with or without RA. Summary of Background Data. VA injury is a potentially serious complication during atlantoaxial transarticular screw fixation. Although this operation is frequently performed on RA patients, there have been few comparative studies on the morphologic risk of VA injury between RA and non-RA patients. Methods. A total of 107 three-dimensional computed tomography images of the cervical spine including the C1 - C2 complex were evaluated. Forty-seven RA patients and 60 non-RA patients were included in the study. The maximum atlantoaxial transarticular screw diameter (MSD) that could be inserted without breaching the cortex was measured 3-dimensionally using a computerassisted navigation system. A high-riding-VA carrier was defined as a patient with either MSD of 4 mm or less. In RA patients, the space available for the spinal cord in flexion (SAC in flexion), duration of disease, RA stage, and type of disease were examined. Results. In the RA group, 45 of 94 MSDs (47.9%) were 4 mm or less, and 33 of 47 patients (70.2%) were highridingVA carriers. In the non-RA group, 11 of 120 MSDs (9.2%) were 4 mm or less, and 9 of 60 (15.0%) patients were high-riding-VA carriers. MSD, C3 A-P diameter, and the ratio of MSD to C3 A-P diameter were significantly smaller in the RA group than in the non-RA group. Multiple logistic regression analysis showed that SAC in flexion was a significant risk factor for a high-riding- VA carrier in the RA group. Conclusion. RA was a significant risk factor for the presence of a high-riding VA. When performing atlantoaxial transarticular screw fixation, particularly on RA patients, thorough preoperative evaluation of the bony architecture is of great importance to avoid inadvertent VA injury.