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.