Use of intraoperative X-ray to differentiate between reducible versus irreducible atlantoaxial dislocation

BACKGROUND: The treatment and classification of atlantoaxial dislocations (AADs) remain controversial. Here, we utilized intraoperative X-ray to differentiate between reducible and irreducible AADs. METHODS: Five patients were diagnosed as having irreducible AAD on dynamic and post-traction X-rays. Under general anesthesia, they were placed prone in a neutral position utilizing skeletal traction. The X-rays and motor evoked potential (MEP), were then monitored before, during, and after placing a thumb on the C2 spinous process and pushing it anteriorly to attain reduction. RESULTS: The intraoperative X-ray confirmed reducibility of AAD in four patients; they subsequently underwent a C1–C2 posterior fusion, which maintained that reduction. For the one patient with an irreducible AAD (despite thumb maneuver), an anterior release was required first to attain reduction, followed by posterior C1–C2 fusion. CONCLUSION: Here, we divided irreducible AAD into two categories: a) reducible—utilizing a thumb maneuver to compress/push the C2 spinous process forward with the patient positioned prone and b) irreducible—those who cannot be reduced with this technique. A posterior only approach was sufficient for those with “reducible” AAD, whereas those who could not be reduced required an anterior release followed by posterior fusion.