Chapter 94 Cervical Facet Dislocations

A Ventral Surgical Strategy for Decompression, Reduction, and Stabilization

Much controversy surrounds the management of subaxial cervical subluxations resulting from facet fracture-dislocation.^1–11 An initial attempt at closed reduction using skeletal traction is not without risk.^12–18 The most serious complication of cervical traction and closed reduction is the retropulsion of disc fragments into the spinal canal and resultant spinal cord compression (Fig. 94-1). Several reports of neurologic deterioration after closed reduction in the setting of concurrent disc herniation have been described.^19–23 In addition, late instability is relatively common in patients treated with closed reduction alone, because of the concomitant presence of significant ligamentous disruption associated with these injuries.

FIGURE 94-1 A typical bilateral facet dislocation with disc extrusion. A, Note that the spinal cord is compressed predominantly by the dislocated caudal vertebral body and rostral lamina before reduction. B, After reduction, the large fragment of extruded disc has been retropulsed into the spinal canal (arrow), resulting in spinal cord compression.

(From University of New Mexico, Division of Neurosurgery, with permission.)

The surgical technique for the open reduction of unstable cervical dislocations varies from surgeon to surgeon. Most reports have described dorsal reduction techniques.^{20,21,24–29} However, the ventral surgical approach for reduction has its advocates.³⁰ Several small series have been published that describe the technique of ventral reduction of locked facets.^19,31–35 Because of the popularization of dorsal fixation techniques (e.g., lateral mass plating and spinous process wiring), ventral reduction has not been widely used in clinical practice. However, an increasing concern has been raised regarding the danger associated with the dorsal reduction of a cervical spine dislocation in the presence of a ventral disc herniation.^19,21–24 Furthermore, because of the common coexistence of significant dorsal bony and soft tissue disruption, a three-vertebral segment (two-motion segment) dorsal fixation is commonly required to stabilize a two-vertebral segment (one-motion segment) instability. In addition, in dorsal reduction of locked facets, it is commonly necessary to remove a significant portion of the involved facet(s), thus often mandating a three-vertebral segment dorsal fixation procedure. Conversely, ventral reduction may be followed by arthrodesis of only a single-motion segment, thus sparing additional motion segments from arthrodesis.

Kwon et al.³⁶ concluded that both ventral stabilization and dorsal stabilization for unilateral cervical facet injuries were valid treatment options. In this randomized study of 42 patients with unilateral cervical facet injuries, patients on whom a ventral approach was used had a lower rate of wound infection, had a higher rate of radiographically demonstrated union, and healed in a more lordotic sagittal alignment. However, they also more frequently had signs of dysphagia and voice changes in the early postoperative period in comparison to the group treated with dorsal stabilization. Patients undergoing a ventral approach should be informed of these (and all other) risks.

Surgical Technique

Discectomy

The standard ventromedial approach is used through a transverse skin incision. After radiographic confirmation of the operative level, a discectomy is performed. A special consideration in the case of facet dislocation is the ventral translation (ventrolisthesis) of the rostral vertebral body on its caudal counterpart. This is often associated with some degree of kyphotic angulation and a resultant obscuration of the disc space, necessitating removal of the ventral aspect of the caudal end plate of the rostral vertebral body with a high-speed air drill (Fig. 94-2). Care must be taken not to remove so much of the vertebral body as to preclude ventral screw-plate fixation. After exposure of the disc space, a standard discectomy is performed. The posterior longitudinal ligament is always removed, thus exposing the dura mater and ensuring adequate decompression.

FIGURE 94-2 The ventrocaudal aspect of the rostral vertebral body obscures visualization of the disc interspace, necessitating partial resection.

(From University of New Mexico, Division of Neurosurgery, with permission.)

Reduction

After completion of the discectomy, deformity reduction is attempted. Often, simple distraction is successful, because a potentially significant obstruction to reduction (the disc and anulus fibrosus) has been removed. However, if this maneuver fails, one of two intraoperative maneuvers may be used to facilitate reduction through the ventral approach: the interbody spreader technique or the vertebral body post technique. Failure to use either technique appropriately may result in failure of reduction.

Interbody Spreader Technique

A Cloward interbody spreader, or an equivalent device, is inserted into the disc interspace at a 30- to 40-degree angle (Fig. 94-3A). Failure to place this device at an angle results in achieving only distraction force application (as simple distraction with tongs achieves). This does not result in the application of a bending moment, which is required for reduction with this technique.

FIGURE 94-3 The interbody spreader technique for reduction of locked facets. After completion of discectomy, the spreader is placed into the disc interspace at a 30- to 40-degree angle. A, Note that the blades of the spreader should be placed deep enough to provide an adequate bending moment. B, The application of traction (thick arrow) and the simultaneous opening of the appropriately placed spreader (thin arrows) create a bending moment and distraction of the disc interspace. C, The application of a dorsally directed force by the spreader on the ventrocaudal aspect of the rostral vertebral body results in the realignment of the disengaged vertebrae.

(From University of New Mexico, Division of Neurosurgery, with permission.)

While distraction is gradually applied with the disc interspace spreader (applied in the midvertebral body region) (Fig. 94-3B), the spreader is rotated rostrally. This applies a bending moment to the dislocated vertebral body while the facet dislocation is reduced by distraction. If the locked facets are disengaged, the vertebrae should realign. Distraction is then relaxed in the aligned position, and the spreader is removed (Fig. 94-3C).

For bilateral facet dislocations, the intervertebral spreader should be placed in the midvertebral body region. For unilateral dislocations, the spreader should be placed on the side of the dislocation to facilitate the application of a torque about the long axis of the spine via the spreader. Placement of the intervertebral spreader too far ventrally may result in fracture of the end plate.

Vertebral Body Post Technique

If the aforementioned technique fails, the vertebral body post technique may be attempted. This technique uses a vertebral body distractor post. It is important to remember that parallel distraction via the vertebral body posts is equivalent to simple traction, in that these techniques do not apply a bending moment.

The vertebral body post technique usually involves placing the posts at an angle with respect to each other (Fig. 94-4A). This facilitates the application of a bending moment that unlocks the facets before the application of distraction forces (Fig. 94-4B). Distraction should then allow for complete disengagement of the locked facets. Manual reduction via the placement of the dorsally directed pressure on the rostral vertebral body encourages reduction if the facets have been adequately disengaged (Fig. 94-4C). Relaxation of the distraction forces then allows reengagement of the facets in a normal position. The placement of dorsally directed pressure on the rostral vertebral body, as described previously, may also be applied with the interbody spreader technique.

FIGURE 94-4 The vertebral body distractor post technique. A, Placement of the posts at an angle with respect to each other allows for the application of a bending moment that helps disengage the dislocated facet joints. B, The application of distraction forces (arrows) results in realignment. Relaxation of the distraction can lead to reengagement of the facets in their normal position. C, Relaxation can be aided by the application of a dorsally directed force on the rostral vertebra.

(From University of New Mexico, Division of Neurosurgery, with permission.)

As an aside, unilateral facet dislocation reduction through a ventral approach may be achieved in a similar manner with the application of torque about the long axis of the spine, thus facilitating the reduction of the rotatory component of the deformity (Fig. 94-5). This tends to reduce the rotational component of the dislocation.

FIGURE 94-5 Appropriately placed posts and the application of torque about the long axis of the spine (arrow) can reduce the rotational component of a deformity.

(From University of New Mexico, Division of Neurosurgery, with permission.)

Special Considerations

In contemplating a ventral approach to the dislocated and unstable cervical spine, at least four factors must be considered: (1) the advantage of first performing a ventral discectomy before an attempt at reduction, (2) the feasibility of achieving a reduction by using a ventral approach, (3) the potential need for an accompanying dorsal procedure (failure of ventral reduction), and (4) the ability to obtain a stable construct through an isolated ventral approach. We emphasize that each of these factors must be thoroughly addressed preoperatively.

Ventral Decompression before Reduction

The incidence of extruded cervical disc herniation associated with cervical spine injury has been reported to be 0.7% to 42%.^{19–21,23,37} Reduction of the dislocation with the potential for retropulsion of disc material into the reduced and realigned spinal canal may result in significant spinal cord encroachment.

Several authors have recommended a ventral decompression before reduction when they suspect the potential for reduction-induced spinal cord encroachment.^{19–21,23,38} This relatively uncommon event may occur with either open or closed reduction strategies and is avoided by the removal of the potentially offending disc before reduction (see Fig. 94-1). Although magnetic resonance imaging (MRI) is useful in predicting this event, it probably is not universally accurate. In fact, MRI may demonstrate the absence of intracanalicular disc fragments. Nevertheless, disc material could be retropulsed through a disrupted anulus into the spinal canal during reduction.²⁰

Summary

A ventral approach to cervical dislocation and instability may be appropriate in more cases than was previously thought. The ventral approach facilitates (1) ventral decompression before reduction (thus minimizing the chance for iatrogenic neurologic injury), (2) single-motion segment fixation (in contrast to two-motion segment fixation using a dorsal approach), and (3) stability acquisition through the application of effective ventral fixation techniques (Fig. 94-6).

FIGURE 94-6 Lateral cervical radiograph of a neurologically intact 18-year-old woman who was involved in a diving accident, demonstrating a bilateral C5-6 facet dislocation (unilateral jumped facet, contralateral perched facet). Note the significant focal kyphosis with resultant obstruction of ventral access to the disc space (A). Preoperative T2-weighted sagittal magnetic resonance image demonstrating a traumatic disc herniation at the level of the dislocation (B). Postoperative lateral (C) and anteroposterior (D) radiographs after ventral decompression, reduction, and stabilization.