Traditional Interspinous, Laminar, and Facet Fusion

Summary of Key Points

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Use of multistranded cables has made passage of sublaminar cables safer.
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Passage of the leader wire with the cables is most likely to cause injury with sublaminar passage. Extreme care should be exercised during insertion.
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Use of sublaminar cables is good for adjunctive fixation at the ends of long constructs to prevent screw pullout with the pedicle screw rod systems.
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Sublaminar cable at C1 can be utilized to reduce a subluxation intraoperatively.
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Sublaminar cable fixation at the termini of a long pedicle screw construct can be used in an attempt to prevent proximal junctional kyphosis.

Fundamental to the details of therapeutic intervention, either operative or nonoperative, is an understanding of the biomechanical principles of cervical spine function. These considerations permit the most effective planning of a specific treatment, particularly regarding the details of surgical intervention. Generally, in the cervical region, the major mechanism of injury is transmission of force through the head. The corresponding changes are most often related to flexion, extension, or rotation, with associated axial compression or distraction. Clarification of these factors assists the surgeon in designing the most appropriate procedure. A surgeon subsequently aims to counteract the major force vectors responsible for the principal injury pattern and avoid procedures that accentuate the original directional force vector. The selected method of treatment should be based on the biomechanics of the injury and the experience and preference of the surgeon. This chapter covers the factors predisposing to instability in the subaxial (C3-7) cervical spine and the management of instability, using wire and cable techniques. Allen and colleagues proposed a mechanistic classification based on biomechanical considerations of the injury vectors. Panjabi and White proposed a working classification, especially for acute instability, in which more than 3.5 mm of anterolisthesis or more than 11 degrees of angulation constitutes instability in the lower cervical spine; this classification may be helpful in evaluation. For awake patients who fail to demonstrate radiographic evidence of instability with routine cervical spine films, flexion-extension lateral radiographs can be obtained. These dynamic radiographs, however, should be approached with a level of caution. The situation is often most safely approached initially by computed tomography (CT), with sagittal reconstruction for full definition of the possible injury patterns. If instability is not demonstrated with the aforementioned studies yet is suspected from the increased prevertebral soft tissue swelling or the clinical examination demonstrating concerning neck pain, these patients should be placed in a firm cervical collar and the flexion-extension films repeated in 2 weeks. The elapsed time provides for muscle spasm to abate and allows demonstration of ligamentous instability on the flexion-extension radiographs.

Initial Management

An accident victim with suspected cervical spine injury should have the head and neck immobilized in a firm cervical collar, or with sandbags, before being transported. In the emergency department, after stabilization of the respiratory and hemodynamic status, a rapid neurologic assessment is undertaken. CT scans of the cervical spine are now accepted as the standard of care and used as the first line of imaging in most level 1 trauma centers, with particular attention paid to visualization of the cervicothoracic junction. Subsequent evaluation may be warranted and is discussed in detail later.

Imaging Evaluation

The use of imaging following a negative high-resolution CT scan may be indicated by the clinical scenario. In awake patients, significant neck pain upon examination may warrant further flexion-extension studies or continued use of a cervical collar until pain resolves. The use of magnetic resonance imaging (MRI) in obtunded patients who have a negative high-quality CT is sometimes employed to rule out ligamentous injury in these patients, but it has not been shown to be of clinical benefit in alert patients who are able to participate in a neurologic evaluation. The use of secondary MRI in obtunded patients without gross evidence of neurologic deficit has been increasingly demonstrated to be unnecessary in the face of negative findings on modern high-quality CT imaging ; in these cases, the cervical collar can be removed after CT findings are finalized. The use of MRI in the obtunded patient should be considered on a case-by-case basis only, whereas routine use in low-impact trauma is not advocated. MRI may be of utility in patients with predisposing factors such as older age (> 60), cervical spondylosis, polytrauma or high-impact mechanism, and neurologic deficit without intracranial pathology. The presence of these factors may lead to a higher clinical suspicion of spinal cord injury (SCI), epidural hematoma, or ligamentous instability. It is important to note that flexion-extension films are contraindicated in patients who are obtunded and should not be employed.

Timing of Surgery

Surgery for cervical spine instability may be performed ultra early (within < 6 to 8 hours), early (in 24 to 72 hours), or late (several days to weeks later). The multicenter, international, prospective Surgical Timing in Acute Spinal Cord Injury Study (STASCIS) suggested that early surgery (< 24 hours following SCI) is beneficial and associated with improved neurologic outcome, as determined by American Spinal Injury Association (ASIA) grade. The temporal course of events may be conditioned by the presence of other associated injuries, but generally most surgeons operate on these patients between 24 and 72 hours, unless during this period there is deterioration of the patient’s neurologic status since admission. Deterioration of the neurologic status may suggest corresponding vertebral artery compromise or other events that may indicate consideration for emergent surgery. In patients with partial neurologic injury and nonreduction of the subluxation, the ongoing bony or soft tissue compression may suggest a theoretic advantage to early surgery in reducing secondary neurologic injury; the validity of this concept has not been fully defined, however. Although there is no clear evidence guiding timing of surgery for bony spine fractures alone, data from the orthopaedic literature regarding surgical management of bony fractures in trauma patients suggest that early treatment may also be beneficial. Vallier and coworkers conducted a retrospective study on 1443 adults with multiple traumatic fractures who were treated surgically, of which 102 patients had spine fractures. Definitive surgical fixation of pelvis, femur, acetabulum, and spine fractures within 48 hours was associated with decreased incidence of medical complications and ICU stay, with the authors advocating definitive surgical fixation within 36 hours in patients with a positive response to metabolic resuscitation. Early repair and stabilization further allows rapid mobilization to minimize pulmonary and other complications of immobility. Taken together, the evidence suggests that rapid resuscitation and early management of cervical spine instability (within 24 to 48 hours) with or without spinal cord injury are advantageous.

Operative Techniques

Positioning, Intubation, and Monitoring

Intraoperative multimodal monitoring may be indicated in patients with severe spinal instability or spinal cord injury. There is incomplete evidence to provide a guidelines level recommendation, but use of these techniques should be at the discretion of the operating surgeon. Patients in traction are brought to the operating room in their beds. Flexible fiberoptic intubation (awake or asleep) or video laryngoscopy such as with the GlideScope (Verathon, Bethell, Walsh) may be variably employed to reduce cervical spine movement and subsequent risk of extension injury in unstable patients ; the use of these methods is largely at the discretion of the anesthesiologist and may not be necessary in all cases.

The patient is turned to the prone position, in a firm cervical collar with manual traction applied to the head ring by the surgeon. The head is supported in a cerebellar headrest, and traction is reestablished ( Fig. 67-1 ). A Mayfield three-point head holder can be used if alignment can be maintained without traction. The latter mode of fixation minimizes problems with pressure necrosis of the face and potentially disastrous ocular injury. A lateral cervical spine radiograph is obtained to check alignment after turning and positioning the patient.

Exposure

The neck (up to the occiput) and the area around the iliac crest and posterior superior iliac spine are routinely prepared and draped. A midline incision is made in the neck, with the length of the incision determined based on the number of segments to be addressed. Midline exposure is critical to minimize muscle injury and excessive bleeding. The paracervical muscles are stripped subperiosteally from the spine and laminae and retracted laterally. The possibility of preexisting bony or ligamentous incompetence with associated instability or dural exposure cautions the surgeon to exercise care in the exposure of the dorsal elements. Supported by preoperative imaging information, dissection is accomplished sharply. Blunt dissection and monopolar cautery are avoided when the safety of the neural elements is in question. The dissection is carried to the lateral edge of the facet joints. When possible, the supraspinous and interspinous ligaments are preserved. Once the spine is exposed, a lateral radiograph is obtained with a marker on the spinous process or other appropriate bony landmark to identify the levels to be fused.

Reduction of preoperatively unreduced, unilateral, or bilateral locked (“jumped”) facets should be attempted at this time. The tip of the superior facet is drilled. Using two straight curettes between the adjacent laminae in the “tire-lever” B-type maneuver and working from medially to laterally toward the facet joint, the surgeon removes the superior facet ventral to the inferior facet ( Fig. 67-2 ). In cases in which there is a facet fracture with encroachment into the neural foramen, this fragment of bone should be removed to relieve pressure on the exiting nerve root. The surgeon should always be aware of the potential for a lateral mass fracture that mimics a unilateral facet displacement.

Wire and Cable Fixation

The dorsal anatomic configuration of the subaxial cervical spine favors the use of adjunctive wire and cable fixation techniques. Wire and cable can be passed through and around spinous processes, through facet joints, and underneath the laminae.

Sublaminar passage of wire in the subaxial spine may injure the spinal cord. Thus, most surgeons restrict the use of sublaminar cables and wires to the more capacious upper cervical spine only, avoiding the regions of cervical spinal cord enlargement. The use of flexible cables has improved the safety of sublaminar cable placement. These wires and cables can also be used to hold the bone graft to the spine, lamina, and facets.

For maximum efficiency, the wire and cable should be strong, malleable, and MRI compatible. The cable systems on the market, in addition to fulfilling these criteria, are coupled with high-quality instrumentation and have generated a renewed interest in the use of wiring in the cervical spine.

Interspinous Wiring

Since Rogers first reported a high success rate for cervical fusion with a single, interspinous wiring, numerous techniques for dorsal wiring have been defined. As previously noted, the availability of commercially prepared, braided-wire (cable) systems has improved the technical ease of applying some of these wiring methods. The systems are typically 18 gauge (Songer) and 20 gauge (Codman), with varying characteristics that may offer improved usage in different constructs. Each system is available in stainless steel or titanium, with specific force application limits that are dependent on the specific type of metal. The braided character of the cables markedly improves strength and malleability. These characteristics are not meant to imply a universal acceptance of the cable systems in creating dorsal constructs; some surgeons prefer the less malleable Luque wire, especially when applying compression techniques with spinous process wiring.

After exposure of the appropriate levels in the cervical spine and confirmation by radiography, the process of wiring can begin. For spinous process wiring, a transverse hole is made at the junction of the spinous process and lamina of the most rostral level to be fused. This can be made using a power drill and can be completed with a large towel clip. Care should be taken not to angle the drill ventrally and enter the spinal canal. The use of a right-angled dental drill appliance permits a straight lateral drill path. The leader wire of the cable system is passed through the drill hole at the spinolaminar junction and then carried distally, parallel across the interspace, down to the next most rostral spinous process. The cable ends are then passed in opposite directions around the caudal aspect of that spinous process ( Figs. 67-3A and B ). The cable is tightened with the Tensioner-Crimper, as defined by the recommendations of the system’s manufacturer. The wire can also be looped around the rostral border of the spinolaminar junction of the upper level and then threaded in opposite directions through the drill hole at the spinolaminar junction, before being carried caudally. Alternatively, the cable can be passed in the form of a loop through two drill holes at the base of the two spinous processes to be fused. In multilevel fusion, each level is wired individually, beginning at the rostral end ( Fig. 67-4 ). This latter construct places the majority of the stress between the donor bone and wire, rather than between the spinous process and wire.