Radiographic definition of the anticlinal vertebra in the dog.

The anticlinal vertebra is a point in the caudal thoracic vertebral column at which vertebral anatomic features change. It may be used as a point of reference in diagnostic imaging studies. However, its exact definition and anatomic location are not consistent between anatomic texts. The position of the anticlinal vertebra was evaluated radiographically in 100 dogs, using three different definitions of the anticlinal vertebra. Definition P referred to perpendicularity of the spinous proceses, definition V referred to verticality of the spinous processes, and definition J referred to the orientation of the intervertebral joints. The anticlinal vertebra was assessed to be T11 in 85%, 75%, and 89% of dogs for definitions P, V, and J, respectively. Combining definitions improved the likelihood that the vertebra assessed to be the anticlinal vertebra was T11, if the combination included definition J, but at the expense of loss of sensitivity. The degree of agreement between the definitions ranged from fair to poor. The level of agreement between definitions P and J was improved for small and large dogs and the level of agreement between definitions V and J was improved for medium and large dogs. Compared with large breed dogs, small breed dogs were more likely to have T10 described as the anticlinal vertebra. The presence of transitional vertebra did not affect the position of the anticlinal vertebra. It should not be assumed that the anticlinal vertebra is T11 in all dogs. Care should be taken to define this anatomic feature accurately when using it as an anatomic landmark.