C1-C2 rotary subluxation following posterior stabilization for congenital atlantoaxial dislocation

The authors report a rare complication of C1-C2 rotary subluxation in two children following posterior stabilization for congenital atlantoaxial dislocation (AAD). A patient, with mobile AAD, underwent Brook's C1-C2 fusion while the other, with fixed AAD, underwent transoral decompression followed by Jain's occipitocervical fusion. A pre-existing ligamentous laxity associated with an asymmetrical wire tightening or slippage of the wires due to rotation of the neck in the former, and the drilling of the C1-C2 lateral joints during the transoral procedure in the latter, could have contributed to the rotary subluxation. Both patients presented with persistent torticollis due to fusion in an asymmetrical position with dislocated facet joints. Rotary C1-C2 subluxation, when coexisting with anterior dislocation, has the potential to cause severe and occasionally fatal cord compression. Well defined criteria to diagnose this entity by conventional radiology exist, however, due to the overlap of anatomy, the condition is often overlooked. In the present study, three dimensional reconstruction images using helical computerized tomography were very useful in delineating the subluxation and in planning its surgical reduction and arthrodesis.