Fig. 3

A 56-year-old male patient was admitted for numbness of the right limbs with walking instability for 11 months. Preoperative lateral X-ray showed OO with AAD (a), and some discontinuous bony structures were seen between the anterior arches of the atlas and the axis in computed tomography (CT) sagittal reconstruction (b, c, white arrow). Magnetic resonance imaging (MRI) showed compression of cervicomedullary junction (CMJ) (d). Reduction of the atlantoaxial dislocation by intraoperative high-weight skull traction failed, and reduction less than 50% was classified as type III. Following transoral release and posterior fixation and fusion, satisfactory reduction were achieved (e, f), and MRI showed the elimination of CMJ compression postoperatively (g)