[Radiologic description of the growth plates of the atlas and axis in foals]

Fractures of the first two cervical vertebrae, atlas and axis, may occur in foals for different reasons, e.g. in cases of a fall, going head over heels or when being hit by a hoof. The tentative clinical diagnosis can be confirmed by x-raying the standing animal, with aid of computed tomography in the anaesthetized foal respectively. The growth plates however, and their time of closure have to be considered when interpreting radiographs. In the atlas there are two ventrolateral plates and one dorsomedian cartilagineous plate. Only the dorsal plate, however, can be found in the dorsoventral projection up to an age of about 12 months. The ventrolateral growth plates which have closed at about six months of age cannot be seen in either ther dorsoventral or laterolateral projection. In transversely oriented CT-scans all of the three centres of ossification can easily be made visible in the atlas. In the axis the cartilagineous gaps between the dens axis and the cranial epiphysis as well as the cranial and caudal epiphyseal growth plate can be shown in normal x-radiographs in both planes of projection. Besides this there are growth plates between the corpus vertebrae and the arcus vertebrae in the axis which cannot be seen in either radiographic projection. They become clearly visible in transversal CT-scans and are ossified at the age of three to four months. At the end of the first year the growth plates between the dens axis and the cranial epiphysis have closed. The cranial and caudal epiphyseal plate are gone at an age of about four to five years.