Cervical Facet Dislocations

Gregory Gebauer and Brett A. Taylor

Facet dislocations are flexion-distraction injuries to the cervical spine that result from high-energy trauma. Motor vehicle crashes and falls are common modes of injury, and many patients may present with multiple other injuries in addition to their facet dislocation. Depending on the nature of the dislocation, the presence of associated fractures, and the amount of concomitant soft-tissue injury, the spine may be highly unstable. This instability may in turn lead to neurologic injury. Prompt recognition and treatment are essential for these injuries.

Classification

Facet dislocations represent a spectrum of injury. Allen and Ferguson described four levels of severity: (1) facet subluxation, (2) unilateral facet dislocation, (3) bilateral facet dislocation, and (4) complete dislocation or spondyloptosis. These injuries are often also associated with facet fractures, endplate or vertebral body fractures, and discoligamentous injury. Radiographically, facet subluxation may appear with widening of the facet joint or with the facets “perched,” with the inferior artciular process from the superior level sitting atop the superior articular process from the subjacent level. Unilateral facet dislocations involve frank dislocation of one set of facet joints and subluxation of the contralateral joint. Generally, anterolisthesis of the superior body is less than 25% of anterior-posterior diameter of the vertebral body. Bilateral dislocations may have 50% anterolisthesis or more.

Physical Exam

Any patient suspected of having a facet dislocation should undergo a complete physical exam. As these injuries are associated with high-energy trauma, all patients should have a thorough examination of the head, body, and extremities to exclude any other injuries. A complete neurologic examination is essential and should include evaluation of sensation, motor function, reflexes, and rectal tone and sensation.

Imaging

Historically, all patients suspected of having a cervical spine injury or involved in a high-energy trauma were initially screened with plain-film radiographs. Recently, the increased availability and accuracy of computed tomography (CT) have led to plain films’ being bypassed and patients’ being sent directly for CT scans. The CT scan should include the entire cervical spine, including the occipitocervical and cervicothoracic junctions. The images should be reviewed to identify any associated fractures of the facets or vertebral bodies. Imaging of the thoracic and lumbar spine (either by plain-film radiographs or CT) should be obtained to exclude noncontiguous fracture.

While magnetic resonance imaging (MRI) should be obtained on all patients with a facet dislocation, the timing of the study is a matter of debate (this is discussed further in the Treatment section of this chapter). Regardless of the time, the MRI should be used to evaluate for compression of the spinal cord or exiting nerve roots, herniations and injuries to the intervertebral disk, and ligamentous injury.

Treatment

The treatment of facet dislocation depends on the nature and severity of the injury, the presence or absence of any concomitant fractures, the neurologic status of the patient, and whether or not a reliable neurologic exam can be obtained from the patient. Facet subluxations can represent a spectrum of injury, ranging from relatively minor “sprains,” or injuries only to the facet capsule, to full dislocations that have spontaneously reduced prior to radiographs’ being obtained. An MRI may help to demonstrate the extent of ligamentous injury. Minor injuries may be treated in a hard collar, with frequent radiographs taken to ensure that no late-onset instability has occurred. Injuries that become unstable or that demonstrate extensive soft-tissue injury should be stabilized with surgery.

Patients who are awake and who have complete neurologic injuries should be treated with immediate high-weight reduction. There is no need for MRI prior to reduction. Expedient reduction relieves pressure on the spinal cord as quickly as possible and gives the patient the best chance for recovery. An MRI should be obtained after reduction to identify any sites of continued spinal cord compression and to evaluate for any epidural hematoma. Surgical stabilization is then undertaken.

Controversy exists regarding whether or not to obtain MRI prior to reduction in both patients who are awake with intact neurologic exams and patients with only radicular-type symptoms. This concern is driven by a case report describing a patient who was initially neurologically intact but then underwent anesthesia while a posterior open reduction and fusion was performed. She awoke quadriplegic. Subsequent radiographic evaluation revealed an anterior disk herniation, which was believed to have extruded into the canal during the reduction maneuver. This has led some to suggest that MRI should be obtained prior to any attempt at reduction to identify disks that may be at risk for possible posterior extrusion. These patients could then be treated with anterior discectomy prior to reduction to minimize the risk of further spinal cord injury. However, there is no clear definition as to what constitutes a disk that is at risk for hernitation. If no disk herniation is present, the patient can be treated with high-weight reduction, with careful observation to make sure that there is no change in the neurologic exam.

For patients whose neurologic status cannot be assessed, either because the patient is unconscious, uncooperative, or intoxicated or because there are communication barriers or distracting injuries, an MRI should be performed to assess the patient’s injury fully and to exclude the presence of a large disk herniation. Treatment can then be based on the MRI findings.

High-Weight Reduction

During the course of the reduction procedure, the process should be aborted if the lateral radiograph demonstrates excessive disk space widening, roughly defined at a disk space 1.5 times as great as that of adjacent levels. Likewise, if there is any change in the neurologic status, the weight should be removed and the patient taken for an emergent MRI scan. In addition to a disk herniation, other causes of neurologic injury, such as an epidural hematoma, should be excluded. The patient should then be taken emergently to the operating room for surgical decompression, reduction, and fusion.

Surgery

Surgery is indicated if a reduction cannot be obtained by closed reduction, if there is evidence of neural compression resulting in a neurologic deficit, or if the injury is felt to be unstable even after reduction. The approach selected depends on the goals of the surgery. Most dislocations without significant disk herniations can be treated with posterior instrumentation, reduction, and fusion. A large herniation may necessitate an anterior approach to remove the disk material, followed by reduction, grafting, and plate fixation. Some authors have asserted that anterior fixation alone may provide enough mechanical stability; however, many feel that anterior surgery alone is not sufficiently stable and should be backed up by posterior instrumentation. Injuries that are highly unstable or that are in patients with complete paralysis may be treated with both anterior and posterior fixation to provide maximal stability.

Outcomes

Children with minor subluxations generally heal well when treated with collar immobilization. Soft-tissue healing in the adult patient is less predictable, and surgical intervention is often considered. Some patients may develop persistent neck or radicular pain when treated nonoperatively. These patients may be candidates for elective decompression and fusion. The outcome of patients with unilateral and bilateral facet dislocations depends on the severity of their injuries at the time of presentation and, particularly, their neurologic status. Typically these injuries will require surgical stabilization to prevent redislocation, late instability, and persistent pain.