Meniscus-like synovial fold in the atlantoaxial (C1-C2) joint.

Some of the synovial joints in the human body have a fibrocartilaginous disc interposed between the joint surfaces to absorb or evenly distribute loads. Examples of fibrocartilagenous discs include the intervertebral disc, knee joint meniscus, and triangular fibrocartilages in the distal radioulnar joint and the acromioclavicular joints. The joint capsule and the surrounding tissue from nine cervical spines (18 C1-C2 joints) were dissected and prepared for gross examination and histology. We found meniscus-like synovial folds in 13 of the 18 atlantoaxial joints. These folds were located at the anteromedial and posteromedial aspect of the joint. Each synovial fold was of semilunar shape, with a thickened outer edge and thin inner edge giving a wedge-shape cross section. In one case, the synovial fold was grossly similar in appearance to a knee joint meniscus, and on histological examination there was evidence of cartilagenous metaplasia in part of the fold. The findings are compared with the limited data reported in the literature.