What is an Atlantoaxial Subluxation?
C1(atlas) -C2(axis) have unique mobility compared to the rest of the cervical spine. C1 is connected to the caudal skull and C1-2 are connected by ligaments. Furthermore, there is not an intervertebral disc present between C1-2. The cranial aspect of the C2 has a bony protuberance called a dens, on which an apical ligament attaches the dens to the ventral aspect of the skull. The transverse ligament runs left/right across the top of the dens, and the paired alar ligaments run from the cranial aspect of the dens (next to the apical ligament) laterally to the occipital protuberances of the caudal skull. All the ligaments must be formed properly, as must the dens, for stability of the C1-C2 joint.
Congenital AA subluxation: most commonly the dens fails to ossify, which results in instability of the joint.
Traumatic/acquired: rupture of the ligaments secondary to spinal trauma can result in subluxation of this joint.
What clinical signs are commonly noted with A-A subluxation?
Lesion localization is C1-C5, therefore signs include pain only (about 25% of cases), pain plus proprioceptive ataxia +/- ambulatory tetraparesis (30% of cases), Nonambulatory tetraparesis (25%), tetraplegia (5%).
What diagnostic tests are useful?
Radiographs can diagnose the subluxation, however if trauma is suspected 3D imaging with CT is recommended. Caution should always be exercised when performing any anesthesia or sedation with these patients. DO NOT VENTROFLEX!!
How do we manage it?
Medical: Cervical brace for 2-3 months has been successful in mildly clinically affected, young dogs with early onset diagnosis. Secondary fibrosis at the joint is the goal of medical management. Strict rest, brace placement and pain management as needed is utilized. I typically start here with mildly affected, young dogs with a short clinical history. 60% of patients were successfully managed in this manner (1 study).
Surgical: Successful outcome has been obtained with both ventral and dorsal stabilization, however ventral appears to have less morbidity and shorter recovery. Implant placement allows for more rigid fixation and is recommended for surgical correction. Between an 80-90% success rate is expected, depending on the technique employed.
The online scheduler is now up and running again! I am pushing for more telemedicine type consults (per AVMA recommendations, and common sense) so please feel free to use this service if at all possible.
Stay safe, stay healthy, and keep those consults rolling!