Computed Tomography Variations in Morphology of the Canine Atlas in Dogs With and Without Atlantoaxial Subluxation

Abstract

Computed tomography images of 120 dogs were reviewed to characterize variations in atlas morphology, and to identify breed-specific morphologic features. The neural arch of the atlas was thicker in large dogs and male dogs than in small dogs, having a layer of trabecular bone between the inner and outer layers of compact bone. The transverse processes of the atlas were relatively longer in large dogs than in small dogs. Twelve (10%) dogs had incomplete ossification of the atlas. Incomplete ossification of the atlas was associated with gun dogs. Eight dogs had atlantoaxial subluxation. All eight dogs with atlantoaxial subluxation had cervical signs, whereas none of the seven dogs with incomplete ossification of the atlas unaccompanied by atlantoaxial subluxation had clinical signs referable to that area. Of five dogs with both atlantoaxial subluxation and incomplete ossification of the atlas, four had osseous defects affecting both the intercentrum and neural arch, and one had only an osseous defect affecting the neural arch. There was a strong association between incomplete ossification of the atlas and atlantoaxial subluxation (odds ratio 35.0, 95% CI 7.0-175, P = 0.00002), which supports the hypothesis that incomplete ossification of the atlas predisposes dogs to atlantoaxial subluxation.

CT scan based determination of optimal bone corridor for atlantoaxial ventral screw fixation in miniature breed dogs

“…Furthermore, the atlantoaxial joint has been associated with several malformations affecting solely the dens but not the joint itself or the screw path area . Also, the CT scan study of the canine atlas identified proportionate dimensions of the atlas transverse process length and the lateral diameter of the vertebral canal in dogs, which supports the hypothesis in our match sized population.…”

Cervical myelopathy due to complex Atlanto‐axial malformation including partial atlantal dorsal arch aplasia in a domestic rabbit

“…To our knowledge this is the first description of an affected rabbit. Dorsal arch partial aplasia of C1 is also recognised in humans and dogs and has a suspected congenital aetiology (Currarino et al 1994, Owen et al 2008, Warren-Smith et al 2009, Parry et al 2010, Wrzosek et al 2014, Voorbij et al 2015. A congenital aetiology also seems to be the most likely explanation in our rabbit.…”

“…Dogs without atlanto‐axial subluxation showed no clinical signs of a lesion in the cervical spinal cord ( Parry et al . ). In five dogs minor trauma or increased physical activity caused the initiation of clinical signs ( Owen et al .…”

Flexed radiographic angles for determination of atlantoaxial instability in dogs

“…However, our control sample was selected for breeds known to be affected with AAI to limit any breed or size inconsistencies that could alter the established measurement protocol. This was an important distinction from the McLear and Saunders study design because established differences in atlantoaxial structures have been found in affected and nonaffected AAI toy breed dogs compared with other breeds …”