Hyperextension and/or hyperflexion of the neck have been reported, resulting in (sub) luxation lesions of the occipito-atlantoaxial region, with or without various combinations of vertebral body and articular process fractures. Young, Excitable animals may injure the immature cervical vertebrae by rearing and falling during play or training. Cranial cervical fractures, such as fractures of the axial dens, are therefore more commonly seen in young horses (less than six months old). The physis of the odontoid peg closes by the age of seven to nine months. The axis (C2) has separate centres of ossification for the dens (odontoid peg), head, body and caudal epiphysis. The odontoid peg originates embryonically from the body of C1. This case report describes a fracture of the odontoid process of the axis (C2). Krook and Maylin reported three fractures of the cervical vertebrae in a total of 192 breakdown injuries in the United States, none of which involved the dens. None of these were odontoid peg fractures instead they involved the caudal body of C2. Vaughan and Mason reported 10 fractures of the axis over a three-year period in the United Kingdom. Cervical vertebral fractures are not uncommon in horses but usually involve the more caudal cervical vertebrae. There are seven cervical vertebrae in the horse: C1-C7.
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