Background: The synovial folds of the lateral atlanto-axial joints have not previously attracted significant radiological attention, being small and not routinely demonstrated on conventional MR images. However, they are considered to be a potential source of neck pain and disability, especially following whiplash injury.

Purpose: The purpose of this study was to develop an imaging protocol and measurement technique to determine the normal morphology of the synovial folds in vivo and establish normative values for their dimensions.

Methods: MR images of the cervical spine of 17 volunteers aged 20 to 50 years (mean 31.1, SD 5.9 years) were acquired using a 1.5T scanner. Seed growing and thresholding methods were used to identify the synovial folds and quantify their dimensions.

Results: The median volume of the right ventral and right dorsal synovial folds was 92.01 mm3 and 76.44 mm3, respectively. Left ventral and left dorsal synovial fold median volume measured 79.26 mm3 and 56.44 mm3, respectively. There was a significant difference in volume between the ventral and dorsal synovial folds of the right and left lateral atlanto-axial joints (χ2(3)=17.54, P=.000). The test-retest reliability of the measurement technique was ICC 0.99 and the inter-examiner reliability ICC 0.80.

Conclusion: This study is the first to establish a MR imaging protocol to visualise the synovial folds of the lateral atlanto-axial joints in vivo and quantify their morphology. The normative values established in the present study provide the basis for future studies to investigate the role of the synovial folds in patients with neck pain.