Neuroradiology Case of the Week

Case 32

Larry Buadu, MD, PhD, and P-L Westesson, MD, PhD, DDS

Clinical Presentation: Patient is a 20-year-old male who is status post MVC anterior subluxation at C5-6.

Radiological Findings: Plain radiograph of the cervical spine (Fig. 1) demonstrates a marked anterolisthesis of C5-6 as well as focal kyphosis. CT of the cervical spine with sagittal reconstructions (Fig. 2) demonstrates in addition to marked anterolisthesis of C5-6 bifacetal dislocation. Fractures of the superior facet of C5 (not shown) and the posterior elements of C4 were also present.
   Sagittal T2-weighted MR image (Fig. 3) shows severe anterior subluxation of C5-6 by more than half of vertebral body width. In addition, there is disruption of the anterior and posterior longitudinal ligament as well as the ligamentum flavum. Sagittal proton density weighted images, confirmed bifacetal dislocation. Severe narrowing of the spinal canal of this level with angulation and deformity of the cord is consistent with acute cord compression.

Figure 1: Lateral plain radiograph of the cervical spine showing marked anterior subluxation of C5 on C6

Figure 2A: Sagittal reconstructed CT image shows anterior subluxation of C5 on C6 to better advantage.	Figure 2B: Parasagittal reconstructed CT image shows interfacetal dislocation with the inferior facets of C5 located anterior to the superior facets of C6
Figure 2C: Axial images demonstrate the CT equivalent of the “double facet” sign of bifacetal dislocation (arrows).

Figure 3A: Fat-suppressed mid-sagittal T2-weighted images demonstrate marked subluxation at C5-6 with angulation and deformity of the cord.	Figure 3B: Mid-sagittal proton density weighted images show disruption of the anterior and posterior longitudinal ligaments to better advantage.
Figure 4A
Figure 4B	Figure 4C
Figure 4: Post reduction shows anatomic alignment and minimal area of myelopathy of the cord

Diagnosis: Acute hyperflexion injury with marked anterior subluxation of C5-6, bifacetal dislocation, and cord compression.

Discussion:
   The majority of authors agree that bilateral interfacetal dislocation (BID) is a result of hyperflexion injury very close to the sagittal plane [1]. Others contend that BID results from combined flexion and rotational forces. It is appropriate to consider BID as a flexion injury because it has been experimentally produced by a flexion mechanism [2].
   The pathophysiology of BID includes complete destruction of the posterior ligament complex, the posterior longitudinal ligament, the intervertebral disk, usually the anterior longitudinal ligament and anterior dislocation of articular masses of the involved vertebrae with respect to the articular masses of the subjacent vertebrae [3]. The dislocated articular masses pass upward, forward and over the superior articular process of the subjacent vertebrae coming to rest in the intervertebral foramina so that inferior facet of the involved vertebra lie anterior to the superior facets of the subjacent vertebrae.
   BID may be partial or complete. When the dislocation is incomplete the dislocated vertebrae is anteriorly displaced a distance less than one-half the AP diameter of the vertebral body. The posterior inferior margins of the inferior facet of the dislocated vertebrae may come to rest atop the margins of the superior articular process of the subjacent vertebrae (the “perched” vertebra) or the dislocated articular masses may sit high in the intervertebral foramina. When CT is not immediately available, oblique radiographs with established degree and validity of incomplete BID.
   Beatson [3] has demonstrated experimentally that complete BID can occur only with total disruption of the posterior ligament complex, the intervertebral disk and the anterior longitudinal ligament. Because of these skeletal derangements and soft tissue injuries the dislocated vertebra is anteriorly displaced a distance equivalent to one-half of the AP diameter, or greater of the vertebral body
   Because of its extensive soft tissue damage and dislocated facet joints, BID is unstable and is associated with a high incidence of cord damage [1].

References:

1. White AA, Johnson RM, Panjabi MD, et al. Biomedical analysis of clinical instability in the cervical spine. Clin Orthop 109;85, 1975
2. Selecki BR, Williams HBL. Injuries to the cervical spine and cord in man. Australian Medical Association, Mervyn Archdall Medical Monograph No. 7. New South Wales: Australian Medical Publishing, 1970
3. Beatson TR. Fractures and dislocations of the cervical spine. J Bone Joint Surg 1963; 45B:21