Anatomic study of the synovial folds of the occipito‐atlanto‐axial joints

Abstract

This study was performed to observe and measure synovial folds of the occipito-atlanto-axial joints and to explore their clinical significance. Two hundred ninety eight occipito-atlanto-axial joints from 30 embalmed cadavers of children and 20 of adults were dissected to find the incidence, quantity, distribution, forms, dimension, and histology of synovial folds. Synovial folds were found in most joints in both groups except for the posterior median atlantoaxial joints. Most of synovial folds were crescent-shaped, distributed on the superior aspects of the anterior median atlantoaxial joints, or in the antero-lateral aspects of the atlantooccipital joints and the lateral atlantoaxial joints. Compared to the adult group, the child group had a higher incidence of synovial folds (72.5% joints). The adult incidence was found to be 58.5%. 54.3% of the synovial folds in child were medium size or large size, but only 30.1% of the synovial folds in adult were medium size and there were no large ones. Microscopically, there were three histologic types synovial folds in these cervical joints, and 78.9% of them belonged to adipose type or fibro-adipose type in child, but only 45.8% belonged to the two types in adult. Our data suggest that the larger synovial folds in children may predispose them to an increased rate of entrapment with resultant edema and subluxation of the associated joint complex. This may be the cause why some cervical spine diseases preferentially take place in children rather than in adult, such as benign paroxysmal torticollis'atlantoaxial rotatory deformity and Grisel's syndrome.