Detect, diagnose, and care for a unilateral cervical facet dislocation in your patients

Cervical facet dislocations generally can be divided into two main categories: unilateral and bilateral. Simple unilateral facet dislocations are often stable injuries, despite the common association of a disruption of the posterior ligamentous integrity. The mechanism of injury usually consists of anterior rotation of one side of the vertebra, resulting in rotation about the contralateral facet joint in a pivot-like fashion. In addition to the rotation, the forward flexion leads to the development of the unilateral facet dislocation.

Figure 1: Lateral cervical view

During the injury, the superior facet of the contralateral side moves anterior-superior and over the tip of the inferior articular facet of the involved side, resulting in placement in the intervertebral foramen anterior to the inferior facet, thus assuming a locked position and giving rise to the radiographic “bow-tie” sign.¹ There may be an anterior migration of the superior vertebral body of up to 25% on the segment below. Several associated injuries may be observed, which might include disruption of the nondislocated joint, concomitant fracture of either facet or the complete lateral mass, or partial tearing of the posterior longitudinal ligament, as well as additional bony fractures of the remaining cervical spine.

The clinical presentation of a unilateral facet dislocation is usually one of a high-impact injury in 15- to 50-year-old patients (low impact in patients more than 55 years old). Patients may have torticollis with axial rotation to the contralateral side.

Imaging
Imaging studies usually begin with routine radiography using static positions so as not to induce or worsen potential neurological damage. The cross-table lateral view can be helpful in screening for a dislocation. Unilateral facet dislocation will manifest on a lateral cervical radiograph as a partial overlap of the two articular pillars of the involved segments, giving rise to the bow-tie appearance. In addition to this sign, a decrease in the overlap of the articular processes compared with the articulation superiorly will be noted. Mild anterior subluxation of the vertebral body above may be noted with possible prevertebral soft tissue swelling. Anterior displacement of the superior segment can be apparent, although this is usually less than 25% of the anterior-posterior dimension of the vertebral body.

Additional views cover the remainder of the routine series, including the anterior-posterior lower-cervical view in which the spinous process of the involved segment may sometimes point to the side of involvement. Additional series, including oblique and dynamic views, should not be routinely performed due to the potential for the induction of serious neurological consequences.

Instead, special imaging should be used, especially MRIs to assess associated neurological injuries that commonly occur in conjunction with facet dislocations.² Structures involved in such injuries include ligamentous, capsular, disc, cord, and nerve root damage, as well as levels remote to the site of the primary injury.^3,4 Important consideration should be given to the state of the disc at the level involved since a significant disc extrusion is most commonly associated with a bilateral facet dislocation—management that varies to that of a unilateral facet dislocation.⁵

Treatment
Treatment of a unilateral facet dislocation falls in two distinctive groups—nonoperative and operative. The less commonly used nonoperative approach can be appropriate if there is minimal subluxation involved in the injury. Patients are placed in a collar for a minimum of 6 weeks and should be continuously monitored for signs of displacement. If reduction using skeletal traction with halo immobilization is not successful, then use open reduction.

Figure 2: Anterior-posterior lower cervical

Alternative nonoperative techniques include closed reduction by manipulation under general anaesthetic with fluoroscopy guidance. If this is successful, patients are either placed in a halo vest for 3 months or wired posteriorly with bone-grafting. However, due to the multiplicity of associated complications of unilateral facet dislocations, the operative approach is commonly taken.

It is important for chiropractors to recognize the extent of injury to the osseous and soft tissue structures. Often the injury is unstable. However, after the recovery stage of the injury has passed and instability is not an issue, chiropractors can provide treatment for rehabilitative approaches to restore and stabilize the motion units.

Operative approaches are considered if closed reduction fails, if persistent instability remains after 12 weeks following the injury, or if there is evidence of middle-column involvement that carries a frequent sequel of late instability. Signs of middle-column instability include facet dislocation of more than 25%, widening of the disc more than 1.7 mm, initial displacement of more than 3.5 mm, and an angulation of more than 11°. The surgical approach may be posterior or anterior. The posterior approach allows direct visualization of the articular processes and allows for posterior wiring. The anterior approach provides only a limited view and may further disrupt the disc. However, this approach may allow the complete removal of the disc, eliminating the possible consequence of paralysis from a disc extrusion during the reduction part of the procedure.

Case Study
A young boy fell off the roof and had immediate pain and difficulty moving his neck. He was taken to the hospital, and radiographs were taken as part of the initial evaluation (Figures 1 and 2). The patient was discharged and wore a hard collar for 1 month. He began to develop headaches 1 year later and presented to a chiropractor for evaluation and treatment.

Imaging findings. An anterolisthesis of C2 on C3 of approximately 20% (with respect to the vertebral body of C3) is evident. Interruption of the anterior-inferior portion of the vertebral body of C2 with the presence of a small fragment of bone just inferior to this region exists. Near complete loss of contact between the facet joints of C2–C3 is present. A small degree of prevertebral soft tissue swelling is evident at the level of C2–C3. The intervertebral disc height at C2–C3 is within normal limits. There is deviation of the spinous process of C2 to the right. Lateral flexion to the left of the entire cervical spine is noted. No additional fracture is evident. The remaining discs and articulations appear to be within normal limits. The remaining osseous structures appear to be within normal limits. The soft tissues are unremarkable.

Diagnosis. Near complete, unilateral right facet dislocation of C2–C3. Possible tear-drop fracture of C2.

Recommendations. Special imaging is essential to evaluate associated injury to the spinal cord and soft tissues, using MRI. To further identify the full nature of the region of apparent cortical disruption of C2, computed tomography is necessary to assess the osseous nature of the injury. CP

Michelle Wessely, BSc (Chiropractic), DC, DACBR, FCC (UK/Radiology), is the departmental head of Radiology at Institut Franco-European de Chiropratique, Paris. She completed her fellowship in musculoskeletal radiology at the Department of Osteoradiology, Veterans Affairs Healthcare Center, San Diego, under Donald Resnick, MD, professor of radiology. Wessely provides a film-reading service for chiropractors and lectures to both chiropractic undergraduates and postgraduates in Europe. She can be reached at: mwessely@ifec.net;   michelle_wessely@yahoo.com;   (033) (0)1 45 15 89 10.

References
1.  Yochum T, Rowe L. Essentials of Skeletal Radiology. 2nd ed. Baltimore: Williams and Wilkins; 1996.
2. Leite CC, Escobar BE, Bazan C, Jinkins JR. MRI of cervical facet dislocation. Neuroradiology. 1997;39(8):583–588.
3. Crawford NR, Duggal N, Chamberlain RH, Park SC, Sonntag VK, Dickman CA. Unilateral cervical facet dislocation: injury mechanism and biomechanical consequences. Spine. 2002;27(17):1858–1864.
4. King SW, Hosler BK, King MA, Eiselt EW. Missed cervical spine fracture-dislocations: the importance of clinical and radiographic assessment. J Manip Physio Thera. 2002;25(4):263–269.
5. Vaccaro AR. Nachwalter RS. Is magnetic resonance imaging indicated before reduction of a unilateral cervical facet dislocation? Spine. 2002;27(1):117–118.