Trauma

Trauma is a common indication for dorsal cervical stabilization.² The primary management of cervical spine injuries consists of realignment (when necessary), decompression of the neural elements (when indicated), and stabilization. In the setting of trauma, if the spine is in good alignment and no decompression is necessary, external immobilization may be all that is required to protect the neural elements while healing occurs. This is particularly true when the major cause of the instability is bony injury. Primary ligamentous instability is much less likely to resolve after immobilization; hence early surgical stabilization is often an appropriate consideration in the management of these injuries.

Instrumentation of the dorsal cervical spine should be considered seriously in all trauma victims who require an open reduction or a dorsal cervical decompression. Persistent dorsal ligamentous instability is most appropriately treated by dorsal surgical stabilization; in fact, it is not unreasonable to offer patients with severe ligamentous injuries internal fixation as an alternative to halo immobilization. Fixation across the afflicted level only is usually successful in achieving long-term stabilization in patients with dorsal ligamentous injuries; however, consideration should be given toward incorporating additional levels into the construct in the setting of severe instability³ (Fig. 147-1). Bony cervical spinal injuries may also be stabilized by using dorsal instrumentation. In particular, cervical lateral mass instrumentation may be used in the presence of laminar and spinous process fractures that often preclude the use of many other types of dorsal fixation.

FIGURE 147-1 A, Lateral cervical radiograph demonstrating a C5-6 fracture in a patient with ankylosing spondylitis. B, Internal fixation was achieved with lateral mass plates and rib cabled to the spinous processes. The high degree of instability associated with this injury influenced the decision to obtain fixation two levels above and below the injury. Postoperatively the patient wore a rigid orthosis for 2 months. His fusion was noted to be solid 1 year postoperatively.

Extension instability and injuries of the ventral axial spine have been managed successfully by using multilevel dorsal fixation; however, a ventral approach is usually more appropriate. This is particularly true if the spinal canal is compromised from bone or disc fragments or when a burst fracture is associated with 25-degree or greater kyphosis.^3,4

Neoplasia

Dorsal cervical instrumentation can be useful in the management of instability associated with neoplasia. If tumor resection is performed via an extensive laminectomy and/or a transpedicular approach, immediate internal stabilization may be accomplished with lateral mass plating. The number of motion segments to be instrumented depends on the location and magnitude of the tumor. In the setting of malignancy, the surgeon must be certain that solid fixation is achieved well above and below the affected levels. Significant tumor invasion of the vertebral bodies requires a ventral approach not only for decompression but also for stabilization. It should be remembered that the treatment of benign tumors may also result in cervical instability. This is particularly true when preoperative root and/or cord dysfunction is present and a wide exposure is necessary (e.g., with large neurofibromas).

Spondylosis

Dorsal cervical instrumentation is also useful in the management of spondylotic disease. Proper instrumentation at the time of initial decompression in patients with abnormal segmental motion or absent lordosis markedly decreases their risk of developing postlaminectomy kyphosis. In these cases, instrumentation and subsequent fusion are important to prevent further problems; when a kyphotic deformity has occurred, treatment with dorsal instrumentation alone does not usually provide the optimum result. Almost invariably, ventral spinal reconstruction is the necessary first step needed to correct or halt progressive postlaminectomy kyphotic deformities; dorsal fixation may then be considered as an adjunctive measure in select patients. Dorsal fusion may provide a more successful means of treating patients who experience symptoms from failed ventral arthrodesis than a second ventral surgery.^5,6 In highly selected cases of severe ventral and dorsal spinal incompetence, a combined or staged “360-degree” operation may be indicated.

Osteopenia

It is often difficult to maintain alignment and achieve fusion in severely osteopenic patients regardless of the fixation technique. Osteoporotic spines are also predisposed to screw pull-out, wire cutout, and instrumentation-associated laminar fractures. Increasing points of fixation may be necessary to offset poor bone quality. The use of rigid external orthotics in such patients aids in maintaining stability while fusion occurs.

Imaging

A complete radiographic workup is essential to properly plan and execute any spinal stabilization procedure. This does not mean that every imaging modality must be employed in every patient. MRI is extremely important in the evaluation of cervical pathology because of its excellent multiplanar visualization of the spinal cord, nerve roots, and surrounding soft tissue. Gadolinium contrast MRI studies should be used for imaging possible tumors and infections but have limited benefit in spondylosis. Static plain radiographs provide information concerning segmental and overall alignment and bone quality and should always be obtained. Considering the widespread use of MRI and CT, preoperative radiographs should still be ordered almost routinely. Preoperative radiographs serve as standards against which alignment can be judged after prone positioning and surgery.

Dynamic studies (i.e., flexion-extension lateral views) often provide valuable information, particularly in terms of assessing stability. Although dynamic films should be obtained in most patients, they are not universally appropriate, and judgment must be exercised before obtaining flexion-extension radiographs. Specifically, flexion-extension radiographs should not be obtained in the trauma patient until the potential for significant instability has been ruled out with static films and/or scans.

CT provides better bony detail than MRI and therefore is more useful to define fractures. MRI often complements CT in the trauma setting because of its ability to define ligamentous injury.⁷ Both modalities are useful in assessing the extent of tumor involvement in patients with metastatic malignancies. CT myelograms should be considered in patients who are unable to have MRIs or when the MRI is equivocal, such as when a previous instrumentation artifact obscures adequate visualization. CT allows for evaluation of the transverse foramina and, by proxy, the vertebral artery. Localization of the vertebral artery is important in surgical planning for placement of screws in the cervical spine.

Intraoperative Monitoring

Neurophysiologic monitoring can be used to monitor the spinal cord integrity during surgery. Options include monitoring somatosensory-evoked potentials (SSEPs) and motor-evoked potentials (MEPs). SSEPs represent signal-averaged data often over several minutes and monitor the spinal cord dorsal columns. MEPs are usually associated with patient motion during recording and are therefore obtained episodically. Special anesthesia considerations exist with intraoperative monitoring. The usefulness of intraoperative monitoring is established for intradural tumors and vascular malformations but is unclear for other cervical spine surgeries. The authors rarely employ such monitoring (barring experimental protocols) in treating cervical pathology other than intrinsic tumors, vascular malformations, or severe deformities.

Tracheal Intubation

Awake fiberoptic intubations should be considered in patients with significant preoperative instability. Fiberoptic intubation allows for securing the airway with minimal manipulation and extension of the cervical spine. Awake intubation facilitates awake positioning of the patient. Careful intubation under general anesthesia is an alternative to an awake intubation. The head must be held in the neutral position or traction employed if there is a concern for preoperative instability. External orthoses, manual in-line immobilization, and/or axial traction may be used to limit the motion of unstable segments during intubation and positioning.^8–10

Positioning

The prone position is most frequently used for posterior cervical operations, and positioning the patient is probably more dangerous than intubation because of the possibility of compromising spinal alignment. Awake positioning is a reasonable method of minimizing risk during turning; however, this technique is not advised for uncooperative patients. The surgeon should be responsible for maintaining proper cervical alignment while turning. Neurologic deterioration after positioning warrants prompt physical reappraisal of cervical alignment, evaluation of the amount and direction of axial traction, and radiographic examination. As always, the turn should be performed in a deliberate and controlled manner with care taken to maintain proper cervical alignment. Unstable patients positioned under general anesthesia should have lateral cervical spine films taken after positioning.

Surgical Exposure

The surgical opening should provide adequate visualization, but care should be taken to expose only the levels necessary to safely perform the procedure. Specifically, exposure of articular joints at additional segments should be avoided. The large ligamentous attachments to the spinous process of the axis are preserved when possible. The large ligaments are key in preventing postsurgical kyphosis. Any dorsal supporting structures, such as the interspinous and supraspinous ligaments, should be left intact whenever possible. Exposure should be carried out laterally up to the edge of the lateral mass.

Bony Fusion

Fusion is always part of a cervical instrumentation procedure, and the segments to be fused should be properly prepared. Complete removal of the soft tissues and periosteum from all bone surfaces is required for fusion. The cortex should be scraped with a curet or may be eburnated with a bur. If a drill technique is used, the bur should be of cutting design rather than a diamond. Copious irrigation should be employed while drilling to prevent scorching temperatures, which may inhibit bony fusion. The facet joint is frequently the site of fusion when using dorsal instrumentation. Each facet joint is prepared for fusion by removing all cartilage and scraping or using a bur on the bony joint surfaces. If a dorsal decompression is to be performed as part of the operative procedure, the facet joint is dissected and denuded of cartilage before the laminectomy (or laminectomies) is performed. Theoretically, the longer the spinal cord is protected by the bony and ligamentous dorsal elements, the less the chance of inadvertent intraoperative trauma. Approximation of the bony articular surfaces will result in a successful arthrodesis. Frequently, the lateral mass joint space is packed with autogenous bone to facilitate fusion.

Corticocancellous bone may be obtained from the cervical laminae if a laminectomy is performed. If spinal canal decompression is not warranted, adequate bone for a facet fusion may be obtained from the cervical or upper thoracic spinous processes. Another alternative is to harvest bone from the dorsal iliac crest or a rib.¹¹ Corticocancellous bone is placed over the dorsal elements.

Hemostasis

After the fusion construct (graft plus instrumentation) has been placed, intraoperative radiographs may be obtained to ensure proper alignment and document hardware position. Before closure, every reasonable effort should be made to achieve hemostasis. In lieu of bone wax, which inhibits bony fusion, thrombin-soaked hemostatic gelatin (Gelfoam [Upjohn, Kalamazoo, MI]) can be pressed into denuded bone surfaces. This maneuver can be a great aid for achieving hemostasis and may not decrease the likelihood of achieving a successful fusion. Epidural venous bleeding can be controlled with bipolar electrocautery. Thrombogenic substances such as oxidized cellulose (Surgicel), autogenous muscle, or thrombin-soaked Gelfoam may be placed in the epidural space, but care must be taken not to compress the neural elements.

Cerebrospinal Fluid Leak

If cerebrospinal fluid (CSF) is noted at any time during the procedure, the site of the leak should be determined. Ideally, all dural defects are closed primarily. If a dural violation cannot be directly repaired, such as may be the case if the defect is located laterally or ventrally, fibrin glue may help seal the leak.¹² If a watertight dural closure is not achieved, wound drains should be avoided. In some situations, lumbar CSF drainage will help decrease the risk of developing a CSF fistula or a pseudomeningocele.

Wound Closure

The wound should be closed in layers with interrupted suture. Removal of the dorsal portion of a prominent C7 and/or T1 spinous process can be extremely helpful for limiting wound tension in slender patients. If local irradiation has been performed or is anticipated, nonabsorbable suture should be considered, at least for the fascial closure. It may be wise to close the entire wound with such suture in these patients. Wound drain placement should be individualized. Some completely dry wounds need no drain; however, if there is oozing from the raw bone surfaces, it may be prudent to place a drain. This is particularly important if a laminectomy has been performed. All wound drains should be tunneled and exit via a separate stab incision.

Luque Instrumentation

Stainless steel pediatric Luque L-rods and Luque rectangles (Zimmer, Warsaw, IN) may be used to stabilize the cervical spine.¹³ The rectangular construct provides greater torsional stability than the L-rods and is therefore preferable. These devices are not indicated for one- or two-level fixation but rather multilevel stabilization procedures. Ideally, both the rods and the rectangles are segmentally secured to every level traversed; however, this is not always necessary. Luque instrumentation can be used to bridge dorsal element defects, such as may occur with metastatic malignancies; however, when using this technique, at least two levels of segmental fixation must be obtained above and below the incompetent region. These devices are most useful for fixation extending to the upper cervical spine or crossing the cervicothoracic junction.

For insertion, the majority of the facet should be exposed at each level one wishes to instrument. It is important to choose a rod or rectangle of correct length. The device should not extend above or below the segments at which arthrodesis is desired. When the proper size is selected, the instrumentation is bent to conform to the normal cervical lordotic curve. After contouring is performed, the surgeon should verify again that the length is appropriate. Luque instrumentation can be secured by using wires or braided cables. Cable is stronger and easier to work with than wire. An effort should be made to obtain segmental fixation at every level to undergo arthrodesis.

Laminar, facet, or spinous process purchase may be used. Cervical sublaminar cables are relatively easy to pass, but their use is associated with risk of neurologic injury. Sublaminar wires should be passed with trepidation in the region of the cervical enlargement of the cord; therefore, sublaminar fixation is often limited to the upper cervical segments (C1, C2), C7, and the upper thoracic spine. Spinal canal stenosis is an absolute contraindication to the use of sublaminar wires and cables. Safe passage of sublaminar wires requires opening the ligamentum flavum and directly visualizing the dura mater.

Sublaminar wires and cables should be passed very carefully by using two hands to push and pull simultaneously. When the wires or cables are passed, they should be held taut with heavy clamps hung over the side of the wound. These maneuvers minimize the risk of ventral displacement of the wire or cable. All wires and cables should be passed without the Luque rods or rectangle in the wound. Some epidural bleeding may occur with the dissection and passage of sublaminar wires and cables, but this often stops as the cables or wires are tightened. If the epidural bleeding persists, hemostatic agents such as thrombin-soaked Gelfoam should be employed.