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.

If sublaminar fixation cannot be obtained, Luque instrumentation may be secured to the lateral masses or the spinous processes. Fixation of Luque instrumentation to an articular mass requires removal of the facet cartilage, entry into the joint space, and drilling of the lateral mass. After removal of the cartilage, a dissector such as a Penfield no. 1 or Freer dissector is inserted into the facet joint and a small drill hole made in the inferior articular process at each level to be instrumented. This hole should be placed at midposition of each inferior facet and be oriented perpendicular to the dorsal articular surface. A wire or cable is passed through this hole, and the ends are secured outside of the wound with a heavy clamp. Before the wires are tightened over the instrumentation, the facet joint is packed with cancellous bone chips. Alternatively, the instrumentation may be secured to the spinous processes with either wires or cables alone or in conjunction with Wisconsin buttons.

Securing the Luque instrumentation to the spine is performed in steps. First, the precontoured device is carefully introduced into the wound, and the previously placed cables or wires are positioned around it. L-rods are placed such that the short arm of each L lies beneath the end of the opposite long arm (Fig. 147-2). The wires or cables are tightened sequentially. Tightening is done gradually so that opposing levels are tightened concurrently, thereby minimizing torsional forces. Cables can generally be tightened to 6 to 8 inch-pounds of torque, but this value should be individualized. Excess wire or cable should be trimmed appropriately before closure to avoid future wound problems (Fig. 147-3). Before closure of the wound, bone grafts may be laid on the laminae and/or the lateral masses.

FIGURE 147-2 Illustration of the use of Luque L-rods for stabilization. This figure depicts a wide two-level laminectomy, as may be performed to remove a metastatic lesion, and subsequent stabilization with Luque L-rods. Note how the short arms of the rods are placed under the long arm to improve rotatory stability. Also note that the instrumentation extends several levels above and below the unstable segment and that sublaminar cables are used to secure the thoracic segments, whereas interfacet cable fixation is employed in the cervical region.

FIGURE 147-3 A, Immediate postoperative radiograph of a patient with ankylosing spondylitis and a fracture who was stabilized with a Luque rectangle. Note that the cables are not trimmed flush with the crimps (arrows) but they do not reach the surface of the skin (arrowheads). B, One year later the inferior cable eroded through to the skin (arrow), necessitating a second procedure to trim the cable ends.

Compression Clamps

Another method of internal fixation that requires intact laminae to stabilize adjacent levels across one or two motion segments is the interlaminar compression clamp. These devices include the Halifax clamp (American Medical Electronics, Inc., Richardson, TX) and Apofix (Medtronic Sofamor Danek, Memphis, TN).^14,15 One of the few indications for placement of this device is isolated dorsal ligamentous instability. Although their use in patients with facet injuries and even linear laminar fractures has been reported, they may not be indicated if there is any significant bony injury.² Other contraindications to placement of laminar compression clamps are the presence of significant vertebral body injury or facet fractures. Lack of ventral column support should be treated with ventral reconstruction, and loss of facet integrity will predispose the cervical spine to rotatory instability that this device is incapable of correcting.

Lateral exposure need only be carried to the medial or central portion of the facet. The pertinent laminae, spinous processes, and dorsal surface of the facets are denuded of periosteum and their bony surfaces prepared, as mentioned previously. The ligamentum flavum is detached from the laminae to be instrumented. For the Halifax instrumentation, appropriately sized clamps are selected and placed temporarily into the wound to estimate the minimal amount the jaws must be opened to pass over the laminae to be instrumented. The clamps are removed from the wound and adjusted accordingly. This maneuver saves time and decreases the amount of “fiddling” within the wound itself. A piece of corticocancellous bone is fashioned such that the dorsally placed clamps will tightly wedge it against the laminae. The clamps are tightened in a controlled, alternating fashion. Although unilateral implantation of cervical laminar compression clamps has been reported, optimum results can only be expected with bilateral fixation.¹⁴

The Apofix device is somewhat easier to implant. Each sublaminar hook extends into the tubular longitudinal member. The longitudinal tubes are of slightly different diameters, allowing one to telescope into the other. The hooks are set into position, and bone grafts are placed either between the Apofix instrumentation and the laminae or between the spinous processes. A compression instrument is applied, and the clamps are squeezed together. The tubes are secured in the compressed position by a crimper. The excess tube length is trimmed. The Apofix should be implanted bilaterally. Its design makes it less likely to rotate out of position than the Halifax clamp.

The bony implant is an extremely important part of the construct. It optimizes the chance of obtaining a successful fusion, which is necessary to avoid delayed instrumentation failure. Biomechanically, the interlaminar or interspinous position of the graft enables the entire construct to resist extension. Although compression clamps provide a resistance only to flexion (tension band fixation), if some effort is not made to limit extension at the instrumented segment, they can lose their purchase in extension. The graft also helps maintain proper alignment by acting as a “spacer” between the laminae as the clamps are tightened.

The complication rate for these devices is higher at the atlantoaxial level than in the subaxial cervical spine.¹⁴ This difference is probably due to the large amount of axial rotation that occurs at this level. However, because of the risks of laminar fracture, device dislodgement, and screw loosening associated with laminar compression clamp fixation, the authors believe that if possible, other more effective methods for subaxial dorsal cervical instrumentation should be used.

Hook-Rod Systems

Immediate multilevel fixation may be achieved by using the hook-rod type systems that have been traditionally applied to the thoracolumbar spine. These devices may be used successfully in select cases of cervicothoracic instability.¹⁶ Recently, rod systems have been developed specifically for the cervical spine. These systems primarily achieve rigid fixation by using lateral mass screws attached to the rods. These rods can also be attached to hooks sized to fit the cervical and upper thoracic laminae.^17,18 Avoidance of hook-rod construct complications in the cervical spine begins with a careful and thoughtful assessment of the true need to place such instrumentation.^19–21

Unlike the thoracolumbar spine, hooks are not usually attached to the pedicles and transverse processes, and cervical fixation is therefore limited to the laminae. When used in the cervical region, these devices are most often applied in compression or as “claw”-type constructs. Pure distraction mode will predispose the cervical spine to kyphosis and is therefore not used.

The application of laminar hooks is described in detail elsewhere in this text. The laminar edge is prepared and a hook inserted. Rods bent to match the cervical lordotic curve are attached to the hooks. Whenever possible, the construct should be cross-linked to increase torsional stability. When instrumenting multiple segments, levels not secured with a hook should be fixed to the rods with sublaminar, facet, or spinous process wires. Care should be taken when designing a hook-rod construct for the cervical spine to avoid crowding the spinal canal significantly with the instrumentation.

Lateral Mass Instrumentation

Stabilization of the subaxial cervical spine with lateral mass instrumentation has gained popularity for a variety of reasons.^22–25 Lateral mass screws may be applied from C2 to the upper thoracic spine, and fixation does not depend on intact laminae or spinous processes. Lateral mass screws provide superb flexural stability and resist torsion and extension significantly better than wiring constructs.²⁵ In experienced hands, fusion with lateral mass plates requires significantly less operative time than segmentally wiring rib, iliac crest, or rods to the articular masses. The excellent stability achieved with lateral mass instrumentation can decrease or eliminate the need for postoperative orthotics. Lateral mass plates and screws are more expensive than wire, but this cost may be recouped in decreased operative time, diminished need for extensive orthotics, and improved outcomes.

The disadvantages of lateral mass stabilization include the potential for nerve root and vertebral artery injury. As with all cervical instrumentation, lateral mass screws must be used cautiously in osteoporotic patients, and adequate spinal alignment must be achieved before insertion. Lateral mass screws cannot correct kyphotic deformities, significant translation, or subluxation; therefore, normal lordosis or at least neutral alignment should be achieved before instrumentation with positioning or traction. The small screw sizes (on average 3.5-mm diameter × 14-mm length) are not capable of exerting sufficient force to correct spinal deformities or malalignments. Lateral mass instrumentation is also used to augment anterior decompression and kyphotic deformity reduction.

The standard midline approach described previously is expanded so that the entire lateral mass is exposed at each level to be plated. This is necessary to accurately determine proper screw trajectory and to facilitate surface area for arthrodesis. Dislocated facets must be reduced prior to application of instrumentation. The joint space is prepared for fusion as previously described. Occasionally, the facet joints may be lax and partly separated. Often, this occurs in conjunction with posttraumatic ligamentous instability. In these cases, simple interspinous process wiring approximates and preloads the facet joints, thereby rectifying this problem. If an interspinous process wire is used, it can be left after plating to augment flexural stability. If the dorsal elements are incompetent, approximation of separated facets should be attempted with positional adjustments, if possible.

Screw holes are drilled into the lateral masses. Several screw trajectories have been used. Based on anatomic, biomechanical, and clinical observations, we believe the best trajectory begins 1 mm medial to the midportion of the lateral mass and is oriented 15 degrees rostral and 20 to 30 degrees lateral (Fig. 147-4). Although a screw may be placed into C7 by using the angles mentioned, the lateral mass of this vertebra is very small. If C7 lateral mass fixation is desired, it may be more appropriate to drill by using trajectories that are slightly more rostral and lateral. It is often preferable to obtain pedicle fixation at C7 (as well as at T1). The pedicle may be entered 1 mm caudal to the facet joint. Drilling may continue in a directly ventral course, but a trajectory that angles medially 25 to 30 degrees is more consistent with the anatomic position of the pedicle. The orientation is perpendicular to the long axis of the spine at C7, T1, and T2^26,27 (Fig. 147-5). It is our practice to verify the position of the pedicle by palpation through a small laminoforaminotomy prior to drilling in all cases.

FIGURE 147-4 A, Lateral trajectory for subaxial articular mass drilling. B, Sagittal trajectory for articular mass drilling. Note that the facet joint is packed with autogenous bone.

FIGURE 147-5 A, Medial trajectory for T1 pedicle drilling. B, Sagittal trajectory for T1 drilling.

Screws may also be placed into the pars interarticularis of the axis. This technique is more difficult than placing lateral mass screws, and precision is required to avoid vertebral artery injury. The drill entry site is high and medial on the articular mass. The trajectory is as great as 15 degrees from the medial plane and is about 35 degrees from the long axis of the spine^6,28 (Fig. 147-6). Fluoroscopy is not necessary for subaxial lateral mass drilling and screw placement, but it should be used when instrumenting the C2 pars.

FIGURE 147-6 A, Medial trajectory for drilling of the C2 pars interarticularis. B, Sagittal trajectory for drilling of the C2 pars interarticularis.

The dorsal cortex of the lateral mass is perpendicularly pierced with an awl or drill bit to facilitate initial drilling and limit the potential for deviation from the proposed trajectory. One should use a drill bit that incorporates a depth stop, usually at 14 mm. The diameter of the drill bit must comply with the manufacturer’s recommendation for the particular screw to be implanted. Drilling is performed in a precise and steady manner to limit vibration and inadvertent creation of an irregular or oversized hole. Occasionally, the drill bit will be felt to penetrate the ventral cortex before its entire length is used. In this situation, drilling should stop. All of the holes on one side should be drilled and prepared and a plate or rod placed before drilling the opposite side. The screws used for lateral mass fixation are most frequently 3.5 mm in diameter. Cancellous screws provide better purchase than those with cortical threads. The specific screw type used, however, is generally dictated by the system used. If the screw is not self-tapping, at least the dorsal cortex should be tapped before screw insertion. Safe bicortical fixation is usually achieved with 14- to 16-mm screws. Only rarely are longer screws necessary, and shorter screws are appropriate for smaller patients. Although bicortical fixation is considered superior to unicortical fixation, it is not mandatory.^28,29 Primary pedicle fixation may be achieved with 4-mm diameter screws.

Inadequate screw purchase may result from osteoporosis, an excessively large hole secondary to inadvertent toggling during drilling, or stripping of threads in the corticocancellous bone during tapping or screw placement. Frequently, in these cases, a “rescue” screw of slightly larger diameter will improve bony purchase.³⁰ These are not placed without risk, however, because they may result in a fracture of the lateral mass. Alternatively, a small amount of polymethylmethacrylate may be placed in the hole before screw tightening. Cervical transfacet screws are an excellent choice for salvaging fixation if a lateral mass screw strips. The purchase achieved by these screws is excellent.³¹ In selected cases, one may wish to place additional graft material over the dorsal elements after denuding their periosteum and burring the dorsal cortical surface.¹⁸ Rods are then contoured and secured using set screws. Excessive force using a rod persuader in securing the screws to the rod should be avoided because the small lateral mass screws may dislodge from the lateral mass if force is applied to reduce the screw to the rod. Additionally, the close proximity to the cervical spinal cord can result in slippage and neurologic injury. Securing the rod is facilitated by the small 3.0- to 3.5-mm titanium rod diameters allowing for some rod flexibility.

Screws are generally polyaxial, allowing for greater freedom in orientation of the bone screw in relation the longitudinal rod. Some screws are “favored-angle screws,” allowing for fewer angulations in certain planes and a bias in the way the screw saddle sits on the screw. Lateral offset connectors can be placed if a screw is significantly outside the rod longitudinal axis, as sometimes occurs with the transition from lateral mass screws to thoracic pedicle screws. Final tightening is often achieved using a torque-limiting screwdriver and antitorque instrument. Sets may also include occipital plates and mechanisms to transition to larger rod diameters used in the thoracic spine. Longer screws are often available for upper thoracic pedicle screw placement as well as for C1 placement. Because lateral mass fixation is successful in almost all patients and has little risk, we do not advocate pedicle fixation from C3 to C6 except in unusual circumstances.^32–34

General Complications

Large postoperative wound hematomas can cause significant neurologic impairment. Smaller clots predispose the patient to infection by acting as a culture medium. Before closure, every effort must be made to achieve adequate hemostasis. Avoidance of hypertension and wound elevation and correction of coagulopathies help limit intraoperative hemorrhage. Thrombin-soaked Gelfoam can help decrease bone bleeding. Epidural venous hemorrhage may occur after a laminectomy or after passage of sublaminar wires. Whenever possible, it should be controlled with bipolar coagulation and hemostatic agents. Epidural bleeding associated with sublaminar instrumentation is usually self-limited and stops prior to wound closure. In very rare cases, such bleeding is brisk and does not cease, in which case one should consider exposing the spinal canal and directly attacking the source of hemorrhage.

Maintenance of a subperiosteal dissection plane minimizes muscle bleeding. Most significant muscular bleeding comes from violation of small and medium-sized veins. Bleeding from these vessels can be controlled by the pressure exerted by wound retractors. When the retractors are removed, the wound must be irrigated several times and a Valsalva maneuver performed by the anesthetist so these potential sources of postoperative hemorrhage may be identified and cauterized. Postoperative wound drainage is generally used routinely.

Frequent and regular wound inspection in the early postoperative period allows for the early identification of complications such as a wound infection or CSF fistula. Wound infections should be treated as soon as they are recognized. Wound infections typically manifest as persistent wound drainage. Antibiotic coverage is guided by Gram stain and culture results. Any fluid accumulations should be drained. Areas of loculated infection or regions of devitalized tissue should be treated surgically. If an infection occurs, it may not be necessary to remove implanted hardware, particularly if expeditious treatment is rendered. When an infection persists despite antibiotic coverage or if the construct integrity is threatened or compromised by significant osteomyelitis, it may be necessary to remove the instrumentation. If the instrumentation must be removed, immobilization, external orthosis, or traction may be used to manage instability. Rarely, a ventral stabilization procedure may be useful in these cases. It should be noted that metallic instrumentation may not be threatened by infection and does not usually need to be removed. This is particularly true when the infection remains superficial to the fascia.

The management of intraoperative CSF leaks has been discussed. Postoperative leakage of CSF from the wound should be treated aggressively with surgical reexploration accompanied by lumbar CSF drainage. The possibility of a wound infection must always be considered and definitively ruled out in these patients.

Neurologic Complications

Neurologic complications may be immediate or delayed. The workup of new postoperative neurologic deficits should proceed with great urgency. The possible causes of immediate deficits are numerous. Many instrumentation-related causes of neurologic deficit may be determined radiographically, but the evaluation of these patients must be individualized. Delayed neurologic complications are more likely to be due to instrumentation failures, loss of reduction, or infection. Although evaluation of delayed deficits is dictated by the specific clinical presentation, all such cases should be promptly investigated and appropriate treatment instituted.

Placement of instrumentation may result directly in neurologic compromise. Lateral mass screws have the potential to compress or injure the nerve roots, spinal cord, and vertebral artery. Spinal cord injury secondary to lateral mass screws has not been reported to our knowledge. Anatomic studies support the concept that the spinal cord is not placed at any great risk from lateral mass screw placement. The direction of drill trajectory and screw placement is important for limiting the risk of arterial or root injury. Roy-Camille et al.²⁸ advocate a screw position that begins at the center of the lateral mass, is oriented perpendicular to the long axis of the spine, and is angled 10 degrees laterally. The Magerl technique involves placement of the screw 2 to 3 mm medial and rostral to the center of the lateral mass and a trajectory that runs parallel to the facet joint and is angled 25 degrees laterally.³⁵ Anderson et al.²² suggest screw placement 1 mm medial to the center of the lateral articular mass with trajectory parallel to the facet joints and oriented 10 degrees laterally from the sagittal plane, whereas Cooper et al.²³ recommend placement of the screws 1 mm medial to the center of the lateral articular mass and oriented 10 degrees laterally but perpendicular to the long axis of the spine.

Overall, there seems to be a general agreement that the screw trajectory should be at least 10 degrees laterally and oriented no more rostral than the articular surface of the facet joint to minimize the risk of inadvertent injury to the nerve root or vertebral artery.^26,36 Cadaveric studies that use such a trajectory suggest that the predicted rates of injury to the nerve roots and vertebral artery would be 3.6% or less and 0%, respectively.³⁶ The actual clinical incidence of nerve root injury secondary to screw placement is much less. In a review of 704 lateral mass screw placements in 79 patients, Heller et al.³⁷ reported a 0.6% rate of nerve root injury. Patients with postoperative radiculopathy secondary to malpositioned screws usually improve significantly with removal of the offending screw.

Despite the fear of vertebral artery injury with lateral mass screw placement, vertebral artery injuries are very rare. Lateral angling of the screws is important to minimize the risk of vascular compromise. Vertebral artery injury may or may not be recognized at the time of surgery. There is usually bleeding from the drill hole in the lateral mass, and at times the flow may seem brisk; however, it should never be pulsatile or appear to be under high pressure. When arterial hemorrhage is noted after lateral mass drilling, an attempt may be made to control the hemorrhage by placement of thrombogenic substances and bone wax in the drill hole. A screw may be placed in the hole to control bleeding. Screw placement is not unreasonable if one assumes that (if vertebral artery injury has indeed occurred) the drill has already significantly lacerated the vertebral artery. If the bleeding is refractory to these measures, it may be necessary to expose the vertebral artery for primary repair or occlusion. No contralateral drilling or screw placement should be performed if a vertebral artery injury is suspected intraoperatively, and the patient must be examined immediately on conclusion of the procedure. Vertebral artery injury or occlusion may not be apparent immediately. The development of delayed posterior circulation deficits should alert the surgeon to this possibility. We recommend prompt angiographic evaluation of suspected vertebral artery injuries.

Spinal Complications

Postoperative spinal instrumentation complications usually, but not always, concern failure to maintain immediate or long-term stability. Poorly conceived stabilization procedures probably account for most dorsal cervical construct failures (Fig. 147-7). When a cervical kyphotic deformity is not adequately reduced, the instrumentation rate failure is increased. Instrumentation should be applied judiciously in osteoporotic patients, and in such individuals a 360-degree approach or postoperative external immobilization is very important. Preoperative evaluation and planning are important to ensure that the proposed construct is biomechanically appropriate for the clinical situation.

FIGURE 147-7 Severe C6-7 fracture-dislocation in a patient with only minor neurologic deficit. A, MRI on admission demonstrates significant ventral and dorsal injury. B, Reconstructed CT images demonstrate complete loss of left C6 facet integrity. C, After realignment, lateral mass plate stabilization was performed and the patient was immobilized in a halo for 3 months. D, Lateral radiograph after halo removal demonstrates resubluxation. This loss of reduction could probably have been prevented by either a 360-degree stabilization procedure or by extending the levels of dorsal fixation.

Instrumentation failure may occur without clinical consequence.³ Heller et al.³⁷ observed a 1.3% rate of plate breakage over an average follow-up of 1.5 years. In the same review, the following incidences of screw complications were noted: breakage 0.1%, avulsion 0.1%, and loosening 0.9%. Minor instrumentation failures (i.e., 1-mm screw loosening) or those that occur many months after surgery (i.e., single wire breakage) often do not require treatment. Significant or early postoperative instrumentation failures and loss of reduction must be addressed. The management options include institution of rigid external immobilization, bedrest, and/or cervical traction during healing, or reoperation (either repeat dorsal approach or ventral instrumentation). The decision for appropriate treatment must be made on an individual basis, taking into consideration the patient’s condition and prognosis, degree of bony union and instability, and rationale for initial choice of dorsal surgical stabilization.