Congenital bipartite atlas with hypodactyly in a dog: clinical, radiographic and CT findings.

A three-year-old Border collie was diagnosed with a bipartite atlas and bilateral forelimb hypodactyly. The dog showed signs of acute, non-progressive neck pain, general stiffness and right thoracic limb non-weight-bearing lameness. Computed tomography imaging revealed a bipartite atlas with abaxial vertical bone proliferation, which was the cause of the clinical signs. In addition, bilateral hypodactyly of the second and fifth digits was incidentally found. This report suggests that hypodactyly may be associated with atlas malformations.