The rate of high riding vertebral artery (VA) was investigated, and the rate in rheumatoid arthritis (RA) group was compared with that in non-RA group.

67 consecutive patients were recruited. The male to female ratio was 44: 23. Sixteen patients were diagnosed as RA and 51 as cervical spondylosis. Sagittal reformatted view transecting mid-portion of the atlantoaxial facet joint was obtained and the height of the isthmus and the internal height of the axis were measured using a Picture Archiving and Communication System (PACS). High riding VA was defined as less than 5 mm of isthmus height or less than 2 mm of internal height.

Thirty-six joints (26.9%) and twenty-seven patients (40.3%) showed high riding VA, and there was no significant difference between right and left side (8 right, 10 left, 9 both sides) (p=0.20). There was no difference among age distribution (p=0.06). In rheumatoid patients, the rate of high riding VA (10/16, 62.5%) was higher than in non-rheumatoid patients 17/51, 33.3%) (p=0.04).

Preoperative evaluation of the VA using the reformatted CT should be performed in all patients who plan to undergo atlantoaxial transarticular screw fixation. In rheumatoid patients, possibility of high riding VA should always be considered.