Objective: Craniovertebral settling is a serious complication of rheumatoid arthritis, and a number of radiographic measures at the craniocervical junction are in use to enable its diagnosis. However, these measures are hampered by the overlap of relevant bony landmarks. We aim to establish accurate values for these measures on CT to facilitate early diagnosis of this condition on cross-sectional imaging.
Materials and methods: One hundred men and 100 women who underwent CT that included imaging of the craniocervical junction were retrospectively identified. Patients between the ages of 18 and 49 years were included. Two radiologists reformatted the images in the midsagittal plane and performed a series of measurements as follows: the Wackenheim line, McRae line, Chamberlain line, and McGregor line and measurements obtained using the Redlund-Johnell method and our modification of the method proposed by Ranawat et al.
Results: There were significant differences between the CT values and accepted radiographic measurements for the Wackenheim, Chamberlain, and McGregor lines. The McRae line was the easiest to measure, and the odontoid tip did not cross this line in any patient (distance from line: range, 0.6-10.4 mm). The CT measurements obtained using the Redlund-Johnell method were similar to the radiographic values, and we provide normal CT values for the modified Ranawat method (men > 23.7 mm, women > 24.2 mm).
Conclusion: We propose that the McRae line should be used over other methods when assessing for craniovertebral settling on cross-sectional studies because it is the easiest measure to understand and remember. If the odontoid tip is eroded, the Redlund-Johnell and modified Ranawat methods are alternatives, and we have provided normal CT values for those measures as well.