Traumatic odontoid process synchondrosis fracture with atlantoaxial instability in a calf: clinical presentation and imaging findings

Abstract

A 6-week-old female Simmental calf was evaluated for acute non-ambulatory tetraparesis. Physical and laboratory examinations revealed no clinically relevant abnormalities. Neurological findings were consistent with acute, progressive and painful cervical myelopathy. Radiographs displayed a fractured odontoid process (dens axis) and vertebral step misalignment at the fracture site. A traumatic origin was suspected. Advanced diagnostic imaging was considered to allow better planning of potential surgical stabilisation and to exclude any additional lesions of the cervical vertebral column. However, during trailer transportation to the advanced diagnostic imaging and surgery site, the calf deteriorated neurologically and was humanely euthanised. Magnetic resonance imaging (MRI) and computed tomography (CT) were performed immediately post-mortem for scientific reasons. The MRI examination reflected the radiographic findings and confirmed severe spinal cord compression at the fracture site. In addition, a T2W-hyperintense signal change within the paravertebral soft tissue dorsal to the fracture site was indicative of a traumatic event. CT identified the fracture site at the synchondrosis between the odontoid process and the body of the axis, and this finding was confirmed by post-mortem examination. Advanced diagnostic imaging and post-mortem examination did not identify any other cervical lesion. In summary, this calf was diagnosed with a traumatic odontoid process synchondrosis fracture, which has not been reported previously in calves but presents a challenging and well-known fracture type in young children. This case report indicates that the odontoid process synchondrosis is a potential predisposed injury site and that traumatic odontoid process synchondrosis fractures should be considered as a potential differential in calves with acute cervical pain and/or signs of a cervical myelopathy.

Comparative anatomy and biomechanical properties of atlanto-axial ligaments in equine, bovine, and canine cadaveric specimens

“…Whereas in canines, agenesia or rupture of the atlantoaxial ligaments with an intact odontoid process, has commonly been described as a cause of atlantoaxial instability (9), this is not the case in equids and bovines. Reported cases of atlantoaxial subluxation in these two species were consistently associated with malformation of the atlantooccipital region and/or malformation or fracture of the odontoid process (6). In equids, complete tearing of the ligamentous attachments of the dens and disruption of the atlantoaxial joint capsule are necessary to allow complete luxation of the joint, whereas partial tearing of the ligamentous and capsular support can result in subluxation (3).…”

“…Similarly traumatic hyperflexion or hyperextension of the neck is reported to cause atlantoaxial fractures in horses (3). In calves, cervical trauma leading to atlantoaxial instability is usually attributed to traumatic hyperflexion or hyperextension of the neck by accidents (6). However, the available literature only provides sparse reports on the integrity and the potential role of the atlantoaxial ligaments in cases of observed instability.…”

“…In previously reported bovine cases, mostly the atlantoaxial instability was caused by a congenital malformation of the odontoid process and/or atlanto-occipital fusion (1,2). Only one case of a calf with traumatic atlantoaxial instability associated with an odontoid fracture has been described to date (6).…”