Irreducible Posterior C1-2 Dislocation with Retrolisthesis of Dens: Hindsight from 10 Cases

Posterior C1-2 dislocation secondary to fracture of the dens or os odontoideum is uncommon. Little is known about posterior dislocations in which close reduction fails, requiring intraoperative maneuvers. The objective of this retrospective study was to analyze clinical presentations, factors causing irreducibility, and nuances in the achievement of intraoperative reduction.

The clinicoradiological features of 10 patients with irreducible posterior C1-2 dislocation were studied. Six were posttraumatic, with odontoid fractures, and 4 had os odontoideum. The radiologic images were studied to analyze the cause of irreducibility, and the operative management of these cases was discussed.

The patients with traumatic dislocation had persistent neck pain (n = 6) and early onset (n = 1) or delayed onset (n = 4) myelopathy. The fracture line was oblique, extending anterosuperiorly to posteroinferiorly in all except 1 patient, with fracture fragments distracted in 4 and interlocked in 2. There was associated lateral translation in 2. All patients had facet locking. Intraoperative reduction was achieved in all by unlocking the facets, intrafracture reduction, or both. All 4 patients with congenital posterior dislocations had retrolisthesis of dens with lateral translation. They presented with neck tilt (n = 4) and severe myelopathy (n = 3). They were easier to reduce intraoperatively, but the improvement lesser in comparison with the traumatic fractures.

The posterior C1-2 dislocation associated with fracture of the dens or os-odontoideum is a distinct entity. Lateral translation is often seen with retrolisthesis of the os odontoideum and occasionally in traumatic posterior dislocations. It is necessary to address the cause of irreducibility and achieve multiplanar realignment for a good outcome.