Atlantoaxial dislocation

Abstract

Atlanto-axial dislocations (AADs) may be classified into four varieties depending upon the direction and plane of the dislocation i.e. anteroposterior, rotatory, central, and mixed dislocations. However, from the surgical point of view these are divided into two categories i.e. reducible (RAADs) and irreducible (IAADs). Posterior fusion is the treatment of choice for RAAD. Transarticular screw fixation with sub-laminar wiring is the most stable& method of posterior fusion. Often, IAAD is due to inadequate extension in dynamic X-ray study which may also be due to spasm of muscles. If the anatomy at the occipito-atlanto-axial region {O-C1-C2; O: occiput, C1: atlas, C2: axis} is normal on X-ray, the dislocation should be reducible. In case congenital anomalies at O-C1-C2 and IAAD are seen on flexion/extension studies of the cervical spine, the C1-C2 joints should be seen in computerized tomography scan (CT). If the C1-C2 joint facet surfaces are normal, the AAD should be reducible by cervical traction or during surgery by mobilizing the joints. The entity termed "dolichoodontoid" does not exist. It is invariably C2-C3 (C3- third cervical vertebra) fusion which gives an appearance of dolichoodontoid on plain X-ray or on mid-saggital section of magnetic resonance imaging (MRI) or CT scan. The central dislocation and axial invagination should not be confused with basilar invagination. Transoral odontoidectomy alone is never sufficient in cases of congenital IAAD, adequate generous three-dimensional decompression while protecting the underlying neural structures should be achieved. Chronic post-traumatic IAAD are usually Type II odontoid fractures which get malunited or nonunited with pseudoarthrosis in dislocated position. All these dislocations can be reduced by transoral removal of the offending bone, callous and fibrous tissue.

Anterior and posterior fixation for delayed treatment of posterior atlantoaxial dislocation without fracture

“…Tucker and Taylor12 have shown that in these circumstances the area of the space enclosed by the atlas reduces to 36%, which is just sufficient to avoid cord compromise. In our patient, and in other cases described in the literature, the neurological deficit is consequently mild 3 4 10. The exception to this is the case described by Chaudhary et al where the patient suffered a hyperextension injury followed by hyperflexion.…”

“…It was felt in these patients that the transverse ligament was partially intact, conferring some stability 2. In two cases, there was persistent instability requiring delayed posterior fusion of C1-C2 3 8. In all other cases, open reduction and fixation were required.…”

“…In almost all reported cases in the literature (including this case), patients have multiple facial injuries, particularly over the lower face and jaw, suggesting a direct anterior impact, forcing the neck into hyperextension. A majority of the previously reported cases were road traffic collisions 1 3 4 6–9. In our case, we surmise that there was a sudden relative deceleration and rotation of the atlas, with respect to the axis, as our patient's face struck some scaffolding during his fall.…”

“…However, in these cases, the patients were definitively managed within 48 h of injury before much swelling/scarring could occur. Between 7 and 10 kg of traction has been used to successfully reduce PAAD 2 3 8. In these cases, the dislocation was stable once reduced and could be managed in a hard collar or cervicothoracic orthosis for a period of 3 months.…”

Computed tomography, magnetic resonance imaging and a novel surgical approach of atlanto-axial instability with incongruence in dogs

“…The main characteristic of incongruence is represented by the disruption of this relationship, which was assessed in this study in CT multiplanar images of all affected patients. The combined diagnostic approach described herein, which included both CT and MRI, is consistent with the described approach recently described in veterinary research and used in human medicine for complete evaluation of the cranio-spinal junction [8,14,16,25].…”