The diagnosis of a unilateral facet dislocation can be difficult to identify on initial radiographic examination (8). Although the lateral radiograph provides the best visualization of the rotational deformity, this injury is still often missed. The identification of the actual dislocated facet can be difficult to visualize since the normal facet is superimposed on the injured one. A high index of suspicion and attention to subtle radiographic findings can help to avoid a missed or delayed diagnosis.

The first hint of a rotational abnormality on the lateral radiograph is the apparent translation or listhesis of the vertebral body at the injured level. The rotation of the vertebral body gives the appearance of a change in size (anteroposterior [AP] measurement) and orientation of the body compared to an adjacent level. A second clue involves the appearance of a double shadow of the dorsal vertebral body line of the injured level. On a good lateral view, the normal orientation of the dorsal vertebral body appears as a single line. Finally, there may be the appearance of widening of the dorsal vertebral structures, indicating the damage to the interspinous and dorsal spinous ligaments. The AP radiograph can also be helpful in the diagnosis of a rotational injury by identifying the discontinuity of the spinous processes.

Secondary imaging can confirm the diagnosis of the dislocated facet joint. Sagittal or 3-D reconstruction of computed tomography (CT) images can readily reveal the injury. In a trauma setting, a CT scan can readily reveal the injury as well as any associated facet fractures. The utility of an MRI lies in the ability to identify the extent of any significant disk injury.

The decision of when to obtain an MRI is a subject of debate. Many surgeons proceed with reduction without an MRI in an appropriate awake and cooperative patient after diagnosis of the dislocation. In the case of a patient with a severe neurologic deficit, an early reduction may reduce the duration of spinal cord compression and possibly reduce the extent of neurologic injury. Potentially, there may be a neurologic benefit to immediate reduction in the patient with complete or incomplete spinal cord injury. Since the lack of availability of an MRI may lead to a delay in treatment, optimal neurologic recovery may be compromised. After a successful reduction, the spinal canal is now
decompressed, reducing the potential for further spinal cord injury, and surgical treatment may then proceed at the best time for the patient.

In patients with less severe neurologic deficits or a normal examination, proceeding with a closed reduction before an MRI is done has been documented to be safe in an awake, cooperative patient (9, 10 and 11). The key point to proceeding this way is the systematic evaluation of the awake patient’s neurologic examination during the entire reduction attempt. If at any time during the reduction attempt a patient’s neurologic status worsens, the procedure is stopped and an MRI is obtained with further surgical treatment planned. The most catastrophic outcome during a closed reduction attempt would be the worsening of neurologic status, which may occur because of displacement of a disk herniation causing spinal cord compression and injury (12). Obtaining a prereduction MRI can reveal any significant disk injury or herniation and allow for appropriate treatment. While waiting for the MRI, it is imperative to monitor the patient’s neurologic examination with systematic evaluation. If neurologic worsening appears to be developing, then proceeding with an immediate closed reduction attempt would be recommended to potentially prevent significant further neurologic injury.

Finally, patients with unilateral dislocation with delayed presentation should undergo an MRI before reduction and treatment. Since these patients have already missed the short time window of reversible spinal cord injury as shown in animal studies, the relatively short time it would take to obtain an MRI in this situation would likely be inconsequential. In this situation, the full extent of the injury would be known, and appropriate treatment can be planned and executed.