Rotary Fixation of the Atlantoaxial Joint: Rotational Atlantoaxial Subluxation

Although the anatomy and movements of the atlantoaxial joint are now well documented, much remains unknown regarding pathological conditions of this area. Infections of varying etiologies, as well as trauma, are well-known factors in the production of a forward atlantoaxial subluxation (26, 29, 37, 38). Recently, forward subluxations of the atlas on the axis have been demonstrated in rheumatoid arthritis and ankylosing spondylitis (20, 21, 25, 27, 35), as well as in mongolism (30, 31). Also well documented are the forward subluxations associated with congenital anomalies such as an absent or separate odontoid process or an atlanto-occipital fusion (3, 12, 22, 23, 33). In all these various conditions, there is either a defect of congenital nature, a fracture, or an attenuation or rupture of a ligament to permit the subluxation forward of the atlas on the axis.

A posterior subluxation of the atlas on the axis also becomes possible due to the congenital absence of both the anterior arch of the atlas and the odontoid, a rare anomaly recently described (32).

Also rare is lateral subluxation at the atlantoaxial joint occurring after damage to the transverse ligament (1, 8).

The reaction of the atlantoaxial joint to a less serious injury which results in fixation of the joint in a position of rotation is not well understood, and the discussion of this problem forms the basis of this paper. This condition has appeared in the literature under various synonyms: as rotary dislocation (5), rotation deformity (6), rotational subluxation (17), unilateral atlantoaxial subluxation (13), and an incongruity between C-1 and C-2 (18). Because the outstanding feature is that of fixation of the atlas on the axis in a position normally attained during rotation, the term rotary fixation will be used to describe the condition.