Three-dimensional CT analysis of atlantoaxial rotation: results in the normal subject.

A three-dimensional analysis of atlantoaxial rotation was made by computed tomography in ten healthy subjects. The method described allowed study of spatial relations between C1 and C2 interspace under both static and dynamic conditions, using a projection in a fixed transverse plane. The results demonstrated an axis of rotation for C2 slightly anterior to that for C1. Asymmetric rotation was observed, the separation between the transverse foramina of C1 and C2 being less marked on the side opposite to the direction of rotation of the head. This use of CT and these anatomic findings may be useful in the study of disorders of atlantoaxial rotation and their effect on the vertebral arteries.