Some observations on the posterior and lateral bridge of the atlas.

Six hundred and seventy-two atlas vertebrae of 6 population groups were examined for the presence of a posterior and/or lateral bridge. Of these, 174 (25.9%) presented with partial posterior bridge formation and 53 (7.9%) with a complete bridge. Twenty-six (3.8%) showed some form of lateral bridging. Although controversy exists as to the origin of atlas bridging, the findings of the present study show that aging could be a factor predisposing to complete bridge formation. The clinical significance of bridge formation is discussed with reference to their possible effect on normal vertebral artery function, particularly in rotation.