Morphometry of the synovial folds of the lateral atlanto-axial joints: The anatomical basis for understanding their potential role in neck pain

Purpose Intra-articular synovial folds of the cervical spine are considered to be a potential source of neck pain and disability. The purpose of the present study was to devise and validate a method to determine the normal morphometry of the synovial folds as a basis for understanding their functional and clinical significance. Methods Nine cadaver cervical spines were sectioned in the sagittal plane. The presence of the synovial folds at the lateral atlanto-axial joints was determined and their morphology described. Depth of projection, cross-sectional area and volume of the ventral and dorsal synovial folds of the right and left lateral atlanto-axial joints were measured from sagittal sections and compared. The relationship between synovial fold dimensions and subject age and cartilage degeneration were determined. Repeat measurements were made for the calculation of method reliability, and the water displacement method was used to determine method validity. Results There was a trend for ventral synovial folds to be larger than dorsal synovial folds. There was no correlation between synovial fold dimensions and age and extent of cartilage degeneration. Measurement reliability ranged from intraclass correlation coefficient 0.95-1.00 (intraobserver), 0.95-1.00 (test-retest) and 0.61-1.00 (interobserver). Limits of agreement for the sectional and water displacement methods for the measurement of synovial fold volume were-1.04 ± 3.35 mm ³. Conclusions A reliable method for quantifying synovial fold dimensions was devised. The results of this study provide a basis for the determination and diagnosis of pathologies affecting the synovial folds.