Complete reduction of retro-odontoid soft tissue mass in os odontoideum following the posterior C1-C2 tranarticular screw fixation

Study Design. A case report of os odontoideum with retro-odontoid soft tissue hypertrophy treated by the transarticular screw fixation. Objectives. To present a case of os odontoideum that showed complete reduction of retro-odontoid soft tissue mass caused by atlantoaxial subluxation after the C1-C2 transarticular screw fixation. Summary of Background Data. Hypertrophy of the periodontoid soft tissue has been reported to be associated with chronic atlantoaxial subluxation and progressive myelopathy. While the rheumatoid pannus has been reported to become reduced or disappear after fixation of the unstable segment, the reduction of the hypertrophied soft tissue mass has never been reported in atlantoaxial subluxation of nonrheumatoid origin, especially in the case of os odontoideum. Methods. Posterior C1-C2 transarticular screw fixation was performed in a patient with os odontoideum, who showed signs of progressive myelopathy by the compression of retro-odontoid soft tissue mass and atlantoaxial subluxation. Results. The fixation of atlantoaxial subluxation achieved: not only the complete reduction of the retroodontoid soft tissue mass, but;also clinical improvement of the myelopathy. Conclusions. Posterior atlantoaxial fixation is worth trying in slow progressing myelopathy by the compression of hypertrophy of the soft tissue even in nonrheumatoid atlantoaxial subluxation, thereby obviating the need for direct removal of the mass via the transoral route.