Introduction

The description of locked cervical facets (subaxial cervical articular process subluxation and dislocation) is relatively new in the veterinary field. It was first described by Gibson at Mississippi State in 2018 [1] and later by Woelfel at North Carolina State in 2021 [2]. A previous report in 1986 [3] described a similar condition, but this was not referred to as “locked facets.” In all there are 14 cases described as unilateral locked cervical facets (ULCF) in dogs and all have been at either C5–C6 or C6–C7. In addition, all but two have been a consequence of big dog/little dog confrontations; the exceptions being a result of automobile trauma. The likely mechanism for the malady is a combination of flexion and rotation of the cervical spine. In this chapter, we will describe the surgical management of locked cervical facets in the dog. The incidence is likely much higher than has been reported.

Unilateral Locked Cervical Facets in Humans

This condition is well described in the human literature [4]. In addition, there are also descriptions of bilateral locked cervical facets. In ULCF the treatment remains controversial and is somewhat case dependent. A nonsurgical reduction, a more conservative therapy, uses a halo apparatus; however, anatomical results are reported as poor. In most cases, closed reduction is attempted and, if successful, is followed by surgical stabilization (anterior approach). When closed reduction fails, open reduction is performed using a posterior approach.

Clinical Presentation

Reported cases are overwhelmingly in small or toy breeds and as a result of big dog/little dog encounters [1, 2]; however, one patient was medium sized (Llewelin Setter – 15.9 kg) and was presented after automobile trauma [1]. In addition, other coexisting cervical injuries are possible. In the two dogs in the original report there was also atlantoaxial subluxation [1]. The 2021 report described some axial rotation of the more cranial segments and a variety of fractures including a transverse process, articular process, and a lamina fracture [2]. These findings emphasize the need for advanced imaging of the entire cervical spine to display all components of the spinal/vertebral injury.

The majority of the dogs will present as severely tetraparetic and many can be described as having a central cord syndrome, since the thoracic limbs are often more severely affected than the pelvic limbs and the injury involves the more caudal cervical vertebrae. In addition, some patients will present with respiratory compromise, likely as a consequence of damage to the C5 segment’s contribution to the phrenic nerve [5]. Based on this, it is ideal that the respiratory function of these patients – to include an arterial blood gas analysis – be performed before any sedation/anesthesia is started.

Most ULCF patients are considered emergent and thus require immediate attention, including referral to a specialty hospital. After initial evaluation (usually including complete physical and neurologic exam plus cervical radiographs) a computed tomography (CT) scan is performed (Figure 10.1). A 3D reconstruction of the CT scan is helpful in surgical planning (Figure 10.2). Depending on the severity of the neurologic condition, immediate or next day surgical intervention is recommended.