Preoperative Preparation and Positioning

After informed consent for the surgical procedure has been obtained, patients are brought to the operating room wearing antiembolic stockings. Intravenous and intra-arterial access are secured, and a single prophylactic dose of antibiotic is administered 30 minutes before the skin is incised. In patients with evidence of myelopathy or significant compromise of the vertebral canal, baseline evoked potentials (somatosensory and motor) are measured before the patient is intubated or positioned. Muscle relaxants are avoided during surgery to provide an immediate indication of neural irritation. Patients with posttraumatic cervical instability or preexisting myelopathy undergo fiberoptic or awake intubation with the surgeon in attendance. Patients with preexisting myelopathy may receive methylprednisolone in accordance with the NASCIS III protocol immediately before the procedure begins.²¹ Drug infusion is continued throughout the procedure and is discontinued after surgery when the patient’s neurological examination is stable. A urinary catheter is placed after general anesthesia is induced if the procedure is anticipated to exceed 3 hours. When patients are positioned, bony and soft tissue prominences are carefully padded to prevent pressure sores or peripheral neuropathies.

Before surgery patients are counseled regarding the choice of autograft or allograft for their fusion substrate. Given the slightly lower but comparable rate of anterior cervical fusion using fibular allograft instead of autograft (particularly for single-level procedures) and the opportunity to prevent the complications associated with harvesting a tricortical segment of autologous iliac crest, most of our patients choose an allograft fusion procedure.^20,22 Among the choices for allograft sources, we prefer fibular allograft given its greater compressive strength compared with tricortical iliac crest allograft.^6,20,23,24 An alternative to bone grafts is now available with the emergence of polyetheretherketone (PEEK) implants, which are associated with fusion rates similar to those of bone grafts when used in conjunction with the correct dose of recombinant human bone morphogenic protein-2 placed inside the implant.²⁵

Reported donor site complications after autologous iliac crest harvest include acute and chronic pain, infection, arterial hemorrhage, peripheral nerve injury, pelvic instability, cosmetic deformity, hernia formation, and postoperative hematoma.²⁶ The risk of transplanting HIV-infected bone has been estimated at less than 1 in 1 million when stringent screening criteria are used.^6,24,27 If an autograft is to be harvested from the iliac crest, the appropriate hip is elevated with a towel roll. Patient preference determines the side from which the autograft is removed. An intrascapular roll, tape along the lateral aspect of the arms, and soft wrist ties that can be manipulated by the circulating nurse are helpful adjuncts that facilitate intraoperative radiographic visualization of the distal vertebral column.

We prefer the Caspar head holder (Aesculap, Center Valley, PA) to support the patient’s head and cervical spine (Fig. 297-1). The head is maintained in a neutral position, and the neck is maintained neutrally or is extended minimally with the assistance of a chin strap. The evoked potentials should be observed carefully for any changes, and intraoperative fluoroscopy should be available to confirm the maintenance of cervical alignment (anatomic or best attainable) after positioning is completed. At our institution, the convenience and cost-effectiveness of using cross-table fluoroscopy from the beginning of the procedure are well-established compared with the relative expense and delays associated with obtaining intraoperative plain film radiographs. The importance of fluoroscopy in confirming the operative level, selecting an appropriately sized cervical plate, directing screw trajectories, assessing final screw positions, and evaluating plate alignment relative to the vertebral column cannot be overstated.

FIGURE 297-1 Patient positioning with the Caspar head holder. The patient’s head is maintained in a neutral position by means of an elastic chin strap. The cervical spine is carefully maintained in either a neutral or minimally extended posture to recreate cervical lordosis. Adhesive tape is run along the lateral margin of the shoulder joint and arm and affixed to the foot of the bed to assist with intraoperative fluoroscopic visualization of the distal cervical spine. The tape should not be run directly over the clavicle to avoid a pressure injury to the brachial plexus. An intrascapular roll facilitates operative access by allowing the shoulders to fall below the coronal plane of the cervical spine. Both the scalp leads for evoked potential monitoring and the endotracheal tube (not shown) would be rostral in the operative field.

(Used with permission from Barrow Neurological Institute, Phoenix, AZ.)

Skin Incision

The operative approach is directed from the side that is most comfortable for the surgeon and usually corresponds to the patient’s right side in a right-handed surgeon. It was thought that the recurrent laryngeal nerve is more susceptible to injury given its relatively anterolateral course outside the tracheoesophageal groove when compared with the left side.²⁸ Consequently, some surgeons may prefer an approach directed from the patient’s left side. However, injury to the thoracic duct has been reported as a complication of approaching the caudal cervical spine from the left side.²⁹ Studies have shown that there is no difference in the incidence of recurrent laryngeal nerve injury associated with a right- or left-sided approach.^30,31 If the patient has already undergone a cervical procedure, we pursue operative access from the ipsilateral side. Although this strategy requires contending with scar tissue and altered anatomic planes, it avoids the more daunting possibility of incurring bilateral injury to vagal nerve branches, the unilateral manifestations of which may be subtle and otherwise undetected unless specifically evaluated for after the previous procedure. If a contralateral approach to a previous scar is pursued, we recommend that the patient undergo preoperative examination of the vocal cords by an otolaryngologist to avoid the possibility of bilateral injury to vagal nerve branches.

A general orientation along the cervical spine can be estimated by external anatomic landmarks (Fig. 297-2), but intraoperative fluoroscopy ensures a more precise placement of the skin incision and limits the amount of soft tissue dissection necessary to obtain adequate visualization of the targeted segment of the vertebral column. Preoperative use of the fluoroscope to define the most rostral and caudal levels of exposure necessary for decompression and stabilization also assists in selecting the optimal orientation for the incision. We have found that a transverse incision located within a skin crease is cosmetically superior to a longitudinal incision that follows the medial border of the sternocleidomastoid muscle. When extended adequately (beyond the midline and laterally across the sternocleidomastoid muscle) and accompanied by generous undermining of the platysma muscle, a transverse incision rarely fails to provide sufficient access and visualization to enable multiple corpectomies to be performed with an accompanying fusion and plating procedure. However, the longitudinal incision may be more functional in patients with difficult anatomy or in whom a particularly long fusion construct is required.

FIGURE 297-2 Orientation to the vertebral column may be estimated by palpating superficial anatomic structures. The hyoid bone sits roughly at the level of the C2-C3 disk space. The top of the thyroid cartilage can be estimated as the C3-C4 disk space. The inferior border of the thyroid cartilage can be estimated as the C4-C5 level. The cricoid ring approximates the level of the C5-C6 disk space. The C7-T1 disk space sits approximately one finger’s breadth above the clavicle. The incision is planned according to the level and extent of the pathology. Single-level procedures may be performed with a transverse incision (dashed line) through a skin fold. Multilevel procedures are undertaken with a longitudinal incision (solid line) along the anterior border of the sternocleidomastoid muscle. Our preference is to expose the vertebral column through a transversely oriented skin incision.

(Used with permission from Barrow Neurological Institute, Phoenix, AZ.)

Soft Tissue Dissection and Exposure of the Vertebral Column

After the patient has been prepared and draped, the skin is sharply incised to the level of the platysma muscle. Hemostasis is obtained with electrocauterization, and the platysma layer is traversed or split longitudinally. Early attention to broad undermining of this subcutaneous muscle is greatly rewarded by the rostral and caudal extents of surgical exposure that can be attained. The underlying sternocleidomastoid muscle and tracheoesophageal bundle are identified, and the avascular plane between these structures is developed with careful, blunt dissection. A trajectory medial to the carotid sheath is followed, and the underlying vertebral column is palpated (Fig. 297-3). Comparing the osteophytic topography to preoperative or intraoperative radiographs can often help orient the surgeon along the cervical column, but fluoroscopy is used for definitive localization along the cervical spine. The prevertebral fascia is opened, and the ventral aspect of the anterior longitudinal ligament is cleaned of overlying soft tissue. The medial insertions of the longus colli muscles are elevated bilaterally from the vertebral column.

FIGURE 297-3 The relative anatomy and trajectory for an anterior transcervical retropharyngeal approach to the cervical vertebral column. A plane of dissection is maintained lateral to the tracheol-esophageal bundle and medial to the carotid sheath. Bilaterally, the longus colli muscles are dissected subperiosteally to provide a submuscular pocket for seating the toothed retractor blades. Failure to seat these blades beneath the longus colli muscles properly places the esophagus and adjacent vascular structures at risk for perforation. When the vertebral column is approached anterolaterally, the tendency is to direct decompression eccentric to the contralateral side. Thus, regardless of whether the operative approach is conducted from the patient’s left or right side, it is important to ensure that the ipsilateral neural foramen receives adequate attention and decompression. When anterior cervical plates are applied, the tendency is to place the plates slightly eccentric to the side from which dissection is directed. Ideally, the plates should be applied in as midline of a position as possible to minimize the risk of injuring the vertebral artery and to provide as optimal a biomechanical construct as possible.

(Used with permission from Barrow Neurological Institute, Phoenix, AZ.)

Several self-retaining retractor systems are available for enhancing exposure of the anterior vertebral column. Fundamental to all of these retractors is the requirement to seat their laterally directed blades deep to the longus colli musculature to prevent injury to the adjacent tracheoesophageal bundle or carotid artery. Injury to the vagal innervation of the larynx can result in silent aspiration (superior laryngeal branch) or hoarseness (recurrent laryngeal nerve). Apfelbaum and Kriskovich⁸ have reported that injury to the recurrent laryngeal nerve during anterior cervical surgery is most likely because of compression of the endolaryngeal segment of this nerve against the shaft of the endotracheal tube after the retractor is placed rather than direct injury from dissection. To protect against this neuropraxia, they describe transiently deflating the cuff of the endotracheal tube after placing the self-retaining retractors and then reinflating the cuff to “just seal” pressure. This allows the endotracheal tube to recenter within the larynx and remove pressure from the laryngeal wall. This technique improved the incidence of injury to the recurrent laryngeal nerve, which decreased from 6.4% in 250 patients undergoing anterior cervical plating without this maneuver to 1.7% of the next 650 consecutive patients in whom it was used.

Rostral-caudal exposure can be improved by placing a second retractor perpendicular to the first (Fig. 297-4). Use of the high-speed drill to remove obstructing osteophytes, in conjunction with the superior illumination and magnification offered by the surgical microscope, has significantly diminished the amount of active cervical distraction necessary to confirm adequate neural decompression during a diskectomy procedure. Distraction posts are usually inserted in the vertebrae to improve exposure of the disk space during decompression of the spinal cord and neural foramina. Alternatively, some surgeons maintain vertebral distraction by placing patients in axial traction using Gardner-Wells tongs at the start of the procedure³² or through gentle, even traction applied by the anesthesiologist during graft impaction. If the patient is maintained in tongs during the procedure, it is crucial to remember to release this distraction after the grafting material has been inserted and before the fixation hardware is placed.

FIGURE 297-4 A second, perpendicularly oriented Caspar retractor system assists with rostral-caudal exposure of the vertebral column. These longitudinally oriented retractor blades are without teeth. Alternatively, the Caspar vertebral body distraction posts can be used to help retract soft tissue in this plane. If the latter system is used, the posts are preferentially placed in the vertebral bodies rostral and caudal to those intended for screw placement.

(Used with permission from Barrow Neurological Institute, Phoenix, AZ.)

Discectomy With or Without Corpectomy

Once orientation at the level of pathology has been confirmed, annulotomies are performed and superficial diskectomies are initiated with straight and angle curets (Fig. 297-5A). If an interval corpectomy is necessary, a bone rongeur can be used to resect the anterior half of the vertebral body and the Midas Rex drill (Medtronic, Memphis, TN.) used to complete the deeper aspect of bone removal (Fig. 297-5B). If placement of an allograft strut (fibular) is planned, autologous bone from the vertebrectomy site is saved for packing the hollow center of the allograft shaft. The operative microscope is routinely used to assist with the removal of deeper bone and soft tissues to facilitate safe exposure of the dura. The epidural space is inspected, and posteriorly based osteophytes are removed from the vertebral bodies and foramen to ensure adequate decompression of the spinal cord and nerve roots. Where possible, generous diskectomies are substituted for a corpectomy if adequate neural decompression can be achieved through wide and deep undercutting of the offending posterior vertebral body surfaces. The benefits of avoiding a complete corpectomy include preserving additional sites for screw fixation along the plate and circumventing the higher risk of nonunion or hardware failure that accompanies fusion constructs involving multiple corpectomy segments.^33,34 This latter point is particularly relevant for patients who require multilevel decompressions.

FIGURE 297-5 A, Anterior view of partially completed C3-C4 and C4-C5 diskectomies. The lateral extent of disk removal is the uncovertebral joints bilaterally. If a corpectomy is planned, the adjacent disk spaces are similarly first defined, and superficial diskectomies are performed before the vertebral body is resected. The superficial aspect of the corpectomy can then be performed easily with either a bone rongeur or a Midas Rex (Medtronic, Minncapolis, MN) drill. Typically, we prefer to use the AM-8 Midas bit to perform the corpectomy. B, Sagittal view of a C4 corpectomy. The deeper aspects of the diskectomies and corpectomy are performed under the operating microscope to ensure the safe exposure and decompression of the epidural space. Once the epidural space has been identified at the level of the rostral and caudal disk spaces, the remaining posterior cortex of the interval vertebral body is removed with bone punches.

(Used with permission from Barrow Neurological Institute, Phoenix, AZ.)

When completed, the typical lateral extent of tissue removed for diskectomies or corpectomies spans up to 18 to 20 mm. Reliable identification of the vertebral midline is crucial to ensure adequate decompression of neural tissue and to prevent vascular complications related to injury of the vertebral artery.^35–37 Frequently, severe degenerative disease, traumatic disruption, or scarring from previous surgical procedures result in the loss of the otherwise apparent anatomic midline. Typically, however, several anatomic cues remain and can be used to provide orientation to the midline for both decompressive maneuvers and plate positioning (Table 297-1). Marking the midline of the vertebral bodies with monopolar cauterization before the longus colli muscles are elevated can also provide helpful reference as the procedure progresses. It is also worthwhile to confirm with the anesthesiologist that the patient’s head has not deviated from the midline position established at the beginning of the case.

TABLE 297-1 Anatomic Cues Available for Maintaining Midline Orientation

Bone Grafting and Plate Fixation

Screw-plate application provides immediate rigid fixation of the cervical spine and functions analogously to an internal halo brace. By ideally imparting some combination of load bearing to the vertebral column and load-sharing properties through the graft site, plating systems protect the neural elements from trauma while facilitating the development of a fusion response, respectively. Bone and instrumentation deform and reform as stress is applied.³⁸ Over time, even the most rigid constructs permit some segmental motion across the site of fixation. In the absence of an osseous union, repetitive loading will fatigue an implant to the point of failure through loosening or breakage. Consequently, perhaps the most fundamental principle related to performing rigid internal fixation is that the presence of instrumentation does not substitute for a carefully conceived and meticulously prepared fusion site.^39,40 In the absence of an associated arthrodesis, hardware failure is a time-dependent certainty (Fig. 297-6).

FIGURE 297-6 A, Anteroposterior and (B) lateral views of a patient treated at an outside facility with a failed anterior cervical plate. Note the transversely oriented fracture at the plate’s midline. The rostral and caudal screw sets maintain good position. There is no evidence of arthrodesis spanning the diskectomy site.

We typically use the Robinson-Smith technique for interbody fusion after a cervical diskectomy.⁴¹ Techniques to optimize the chances for successful arthrodesis (Table 297-2) at the operative site can be subdivided into those that (1) enhance the natural capacity for bone healing to occur, (2) minimize the extent of iatrogenically induced impediments to bone graft incorporation, and (3) maximize the biomechanical advantage of the hardware construct.

TABLE 297-2 Techniques to Optimize Fusion-Hardware Construct

Enhancing the Natural Capacity for Bone Healing

Bone grafts are incorporated with the greatest success when the fusion construct is maintained under a compressive load (Wolff’s law).⁴² Consequently, the vertical dimension of the graft material being used is typically sized a few millimeters longer than the measured diskectomy or corpectomy defect to ensure mechanical compression of the graft within the recipient bed. At the time the graft is placed, the adjacent vertebral bodies can be distracted mildly through several techniques (disk space spreader, vertebral body distraction posts, axial traction, or gentle vertical distraction by the anesthesiologist) to ensure that the graft ultimately experiences a compressive load. After the posterior half of the graft has been tamped into place, the vertebral body distraction is released and the remainder of the graft advanced. These maneuvers promote seating and prevent excessive impaction of the graft. When relying on axial traction applied with cranial tongs to achieve vertebral distraction during the decompressive portion of the procedure, it is important not to overlook requesting its release before proceeding to internal fixation.

After final positioning, graft security and an appropriate epidural margin are confirmed by palpating posterior to the graft with a nerve hook and visualizing the posterior border of the graft with fluoroscopy. Before the graft is inserted, all soft tissues are removed from the graft material and fusion interfaces (end plate articular cartilage) to prevent the delayed differentiation of fibrous tissue that might hinder bone formation. The creation of smooth, apposing surfaces along the bone graft and vertebral bodies serve to improve the environment for fusion by maximizing the area of surface contact at the bony interfaces.