Synovial folds of the lateral atlantoaxial joints: In vivo quantitative assessment using magnetic resonance imaging in healthy volunteers

Study Design: Analysis of magnetic resonance (MR) images of healthy volunteers. Objective: To develop and validate an imaging protocol and measurement technique to describe the morphology and quantify the dimensions of the synovial folds of the lateral atlantoaxial joints in vivo. Summary of Background Data: The synovial folds of the lateral atlantoaxial joints are considered to be a potential source of neck pain and headache, especially following whiplash injury. Until recently, it has not been possible to image the synovial folds in vivo and consequently their normal morphology is not fully understood. Methods: MR images of the cervical spine of 17 volunteers (4 male and 13 female) were acquired using a 1.5-tesla scanner. The morphology of the synovial folds at the lateral atlantoaxial joints was described and their presence determined. The volume and cross-sectional area of the ventral and dorsal synovial folds of the right and left lateral atlantoaxial joints were measured and compared. The relationship between the dimensions of the synovial folds and subject age was examined. Twenty synovial folds were measured twice by one observer and once by a second observer for the determination of measurement reliability. Results: There was a significant difference in volume (χ [3] = 17.54, P = 0.000) and cross-sectional area (χ [3] = 18.95, P = 0.000) between the v ntral and dorsal synovial folds of the left and right lateral atlantoaxial joints. There was no correlation between synovial fold dimensions and age. The reliability of the measurements ranged from intraclass correlation coefficient 0.95 to 0.99 (intraobserver reliability) and intraclass correlation coefficients 0.75 to 0.82 (interobserver reliability). Conclusion: MR imaging was successfully implemented as a noninvasive method for visualizing the synovial folds of the lateral atlantoaxial joints and quantifying their dimensions in healthy volunteers. The results of this study provide a basis for future studies investigating synovial fold pathology in patients with neck pain and headache.