OBJECTIVE: To evaluate the occurrence and frequency of abnormalities at the second and third cervical vertebral junction (C2/3) in dogs with and without atlantoaxial instability (AAI).
STUDY DESIGN: Retrospective multi-institutional case-controlled case series.
ANIMALS: One hundred and seventeen dogs with AAI and 117 dogs without AAI.
METHODS: Radiographs, together with computer tomographic images or magnetic resonance images or both, of the cranial cervical spine of dogs were reviewed for the presence or absence of intervertebral disc-related anomalies, osseous fusion of the vertebrae, spondylosis, or any other anomaly of the C2/3.
RESULTS: The incidence of anomalies affecting the C2/3 in dogs with AAI was 38.46% (n = 45) and in the control group it was 11.97% (n = 14). The majority of the observed anomalies involved the intervertebral disc. In conjunction with AAI, intervertebral disc-related anomalies were noted in 33.34%, spondylosis in 2.56%, osseous fusion in 1.71% and a hypoplasia of the spinous process in 0.85% of the cases. Summarized under the term intervertebral disc-related anomalies, a morphological alteration of the intervertebral disc was noted in 10 cases with AAI, characterized by a spherical outer shape and a minimally reduced size and a dorsal positioning in the intervertebral space.
CONCLUSIONS: There is a significantly higher incidence of anomalies affecting the C2/3 in association with AAI. In conjunction with AAI, intervertebral disc-related anomalies are the most frequent pathological finding affecting the C2/3.