Positioning

The patient is positioned supine on the operating table, and general endotracheal anesthesia is administered. If significant spinal cord compression or myelopathy is present, consideration should be given to a fiberoptic nasotracheal intubation on a patient who is awake. After successful intubation, the patient’s neurologic examination results are confirmed to be unchanged before the induction of general anesthesia.

The patient’s head should be supported with either a foam donut or a Mayfield horseshoe headrest. The neck should be supported dorsally with a firm support to prevent intraoperative motion. In addition, an attempt at achieving a normal lordotic cervical curvature should be made to optimize the postoperative sagittal plane alignment. Ordinarily, a degree of neck extension is preferable to improve the lordotic curvature, as well as to aid in the dissection process. This is particularly true for upper cervical dissections. It is important to evaluate the patient’s ability to extend the neck preoperatively and to not exceed this degree of extension intraoperatively. Hyperextension of the neck in a narcotized patient may lead to spinal cord compression.⁴

The operating table is flexed slightly at its midpoint, and a sandbag or other bolster is placed beneath the iliac crest to facilitate bone graft harvesting. All bony prominences must be padded, with particular attention paid to the protection of the ulnar nerves at the elbow. The knees are flexed and the heels are padded. Antiembolic stockings may be placed, and sequential compression devices are used to prevent the development of an intraoperative deep vein thrombosis.

After patient positioning and before preparation, the endotracheal cuff is deflated for 5 seconds and then reinflated. This maneuver was described by Apfelbaum⁴² and has been used to limit compression of the vocal cords at the level of the arytenoid cartilage in the larynx. The recurrent laryngeal nerve (RLN) terminates at the arytenoid cartilage, and if it is compressed by the endotracheal tube, an RLN palsy may result.

A Doppler probe may be used to auscultate a baseline signal for the superficial temporal artery. During intraoperative retraction (of the carotid artery), the Doppler pulse can be reevaluated. If skeletal traction is to be used, the tongs are placed at this stage.

Incision

The selection of the ideal side for approach is controversial, with advocates for both right- and left-sided approaches. As a general rule a right-handed surgeon can approach the operation more easily from the patient’s right side, but the more variable anatomic course of the right RLN may render the nerve more vulnerable to injury during a right-sided approach.^43–45 This vulnerability is particularly true with lower cervical dissections (Fig. 40-1). The reported incidence of postoperative RLN palsies presenting as postoperative hoarseness varies between 0.8% and 3.7%.^{4–7,9,28,43–51} From a left-sided approach, the RLN has a longer course and may be less likely to be injured, but the thoracic duct is vulnerable with left-sided approaches to the lower cervical spine⁹ (Fig. 40-2). In addition, the thoracic duct may be bifid, and injury to one of the limbs of the thoracic duct may not be recognized intraoperatively. If chyle is observed, simple ligation of the thoracic duct is usually all that is necessary. With lower cervical discectomies there is a theoretical risk of pneumothorax or mediastinitis with approaches from either side.^10,16,52,53

FIGURE 40-1. Right-sided low cervical exposure places the right recurrent laryngeal nerve at risk. The regional anatomy is depicted.

(Copyright University of New Mexico, Division of Neurosurgery.)

FIGURE 40-2. Left-sided low cervical exposure places the thoracic duct at risk. The regional anatomy is depicted.

(Copyright University of New Mexico, Division of Neurosurgery.)

It is essential to make the skin incision at the proper level. The most common error is to place the incision too caudal, thereby obligating the physician to operate at an awkward, upward oblique angle. This can limit visibility during the discectomy. It is much easier to gain access caudally from a rostrally placed incision than the converse.

With one- or two-level discectomies a transverse incision is most commonly used. This is placed in a skin fold that allows for a more cosmetic postoperative result. If discectomies at three or more levels are to be performed, an oblique incision that parallels the medial border of the sternocleidomastoid muscle is preferable. This incision is commonly used for carotid endarterectomies because it allows for a better exposure of multiple spine levels. We prefer to make our transverse incisions for lower cervical approaches at the level of the upper border of the crossing omohyoid muscle. This incision will be at the C5-6 level and provides comfortable access to both the C5-6 and C6-7 intervertebral discs. Maintaining the dissection plane rostral to the omohyoid muscle and depressing it inferiorly as necessary has resulted in an extremely low rate of postoperative RLN palsy in our practice.

Dissection

The dissection is carried sharply through the subcutaneous tissue and the platysma muscle. The platysma muscle may be sharply divided in a transverse fashion or split longitudinally for access to the subplatysmal space. As a general rule, transecting the platysmal muscle is preferable for exposures of two or more levels. If access to multiple levels of the upper cervical spine is necessary, a generous subplatysmal dissection is used to limit the extent of soft tissue retraction required to gain adequate exposure. After the subplatysmal dissection is completed the fascia overlying the medial border of the sternocleidomastoid muscle is sharply divided, and the deep dissection is performed, either sharply or bluntly. The plane of the deep dissection is between the sternocleidomastoid muscle and carotid sheath laterally and the trachea, esophagus, and strap muscles of the neck medially. Careful dissection, with identification of the carotid artery by palpation and gentle finger dissection, is required to avoid carotid artery injuries.^6,30,54,55 This trajectory allows for exposure of the prevertebral fascia. In patients who have not undergone previous ventral cervical surgery, blunt dissection is easily and safely accomplished. Excessive soft tissue stretching should be avoided because occasional RLN injury has been hypothesized to be secondary to stretching. In this case, avoiding high endotracheal cuff pressures may reduce the incidence of such injuries.⁴²

In patients who undergo reoperation sharp dissection may be necessary. It is important to confirm that the dissection remains dorsal to the hypopharynx and the esophagus. With reoperation, a nasogastric (NG) tube should be placed. This may be palpated to confirm the location of the esophagus and hypopharynx. The incidence of hypopharynx perforation during upper cervical discectomies varies between 1%^8,46,47,56 and 5%.^48,57,58 Esophageal perforation has also been reported in cervical discectomies.^47,59–64 If the hypopharynx or esophagus is penetrated, a drain should be placed, a layered closure performed, and an NG feeding tube inserted. The latter must be maintained for at least 1 week postoperatively to allow for the soft tissue to heal and prevent the development of a fistula.

If there is a question of perforation of the alimentary tract, the NG tube should be withdrawn so that the tip of the tube is in the esophagus. After this maneuver, instillation of a colored inert dye, such as methylene blue or indigo carmine, should assist with demonstration of the violation. Unrecognized esophageal perforations can lead to the development of deep soft tissue infections (including mediastinitis). These manifest as high fevers, severe retrosternal pain, and subcutaneous emphysema. Other severe complications of esophageal perforation include esophagocutaneous fistula⁵⁷ and even death.⁶¹

Retraction

On entering the prevertebral space a radiographic marker must be placed and a lateral cervical spine radiograph obtained. This mandatory step ensures that the operation is performed at the correct level. There have been reports of ACDs being performed at the wrong level.^2,9

Establishing that the correct level is being operated on is readily accomplished by placing a radiopaque 18-gauge spinal needle into the intervertebral disc space and obtaining a lateral fluoroscopic image. Alternatively, the authors prefer to place the spinal needle into the ventral aspect of the vertebral body cortex rather than the intervertebral disc, which avoids perforation of the anulus. Should the first attempt at localization demonstrate exposure of an intervertebral disc not to be operated upon, perforation of the outer anulus with a spinal needle may lead to accelerated adjacent-segment disc degeneration at this level. Thus, placement of the spinal needle through the ventral vertebral body cortex potentially avoids this complication.

When the appropriate level has been identified, it is useful to mark the true anatomic midline. This is best accomplished by marking a point midway between the most medial borders of the longus colli muscles. After the midline is identified, the longus colli muscles are elevated from the vertebral bodies and discs bilaterally. Longus colli dissection should be limited laterally to 3 mm of muscle. If the longus colli muscles are dissected excessively, a Horner syndrome—the triad of ipsilateral ptosis, myosis, and anhydrosis—may result. The incidence of postoperative Horner syndrome varies from 0.2% to 2%^{2,4–6,46,47,65–67} after ventral cervical spine surgeries.

After the longus colli muscles are elevated, a self-retaining retractor system is used. Toothed retractors are placed under the longus colli muscles bilaterally. With single-level discectomies there is rarely a need to place vertical self-retaining retractors. When operating on the lower cervical spine, it is essential to avoid retraction of the RLN, which is particularly problematic when a right-sided cervical approach is used. If necessary, vertical retractors should be smooth at the tips, and care should be taken to avoid excessive retraction.

The self-retaining lateral retractors should be carefully placed to avoid excessive retraction on the esophagus, which may lead to postoperative dysphagia. The exact mechanism responsible for the development of postoperative dysphagia is unknown; however, it is thought that retraction-induced pressure on the esophageal wall leads to local ischemia with subsequent hyperemia and swelling.⁶⁸ This in turn may lead to postoperative dysphagia. A mild, transient, postoperative dysphagia is common after ventral cervical surgery. However, in the majority of patients this resolves within 3 months.^69–71 Dysphagia rates have been reported to vary from 1.8% to 9.5%,^{1,7,10,17,27,28,48,53,69–72} to between 21.2% and 35%.^5,9,46 Intermittently releasing the retractor pressure during prolonged surgical procedures helps to avoid this complication. Most dysphagia episodes are transient and do not require a gastrostomy tube. In cases of severe postoperative dysphagia, a gastrostomy tube may be needed for enteral feedings.

Excessive lateral retraction may also compress the carotid sheath. In patients with significant preoperative atherosclerosis, prolonged pressure against the carotid artery can lead to thrombosis with cerebral ischemia. To avoid this problem, after the lateral self-retaining retractors have been placed, the pulse of the superficial temporal artery above the level of the zygoma may be auscultated with a Doppler probe or palpated by the anesthesiologist intraoperatively. This measure confirms blood flow in the external carotid artery. Because the common carotid artery bifurcates into its external and internal branches at the C3-4 level, this maneuver indirectly increases the degree of confidence that blood flow in the internal carotid artery has not been significantly compromised. In addition, the retractors may alter the position of the endotracheal tube. Release of the endotracheal tube cuff for 5 seconds, followed by re-inflation to the lowest pressure that eliminates air leak, confirms that the vocal cords are not being excessively compressed.⁴²

Distraction

After the retractors have been firmly positioned, the anulus fibrosus is incised and the ventral two thirds of disc material is removed with a combination of rongeurs and curettes. Distraction techniques may improve the visualization of the disc interspace. Commonly, Gardner-Wells tongs are placed before draping, and additional weights may be added to augment distraction. Holter distraction may also be used. Improved visualization may be achieved by the use of intervertebral body disc spreaders. Alternatively, posts may be placed into the vertebral bodies above and below the desired disc exposure, with a distractor placed over the posts.

After the distractor is placed, an operating microscope may be used to improve the magnification and lighting. Alternatively, a head light or high-quality overhead light, with or without loupe magnification, may be used. Adequate visualization is essential for performing the discectomy procedure safely. We routinely utilize the operating microscope in all ventral cervical spine surgeries.

Discectomy

The adequacy of neural decompression is directly related to the completeness with which the discectomy itself is performed. In addition, most neurologic complications occur at this stage of the procedure. The disc is removed, including the entirety of the dorsal anulus fibrosus in the midline. The depth of the dissection necessary to achieve this may be estimated from the preoperative MRI and CT scans. Small, upbiting microcurettes and rongeurs allow for removal of the anulus fibrosus. Hemostasis is achieved with judicious use of bipolar electrocautery, hemostatic gelatin (Gelfoam) soaked in thrombin, and cotton patties. After removal of the anulus fibrosus, the underlying posterior longitudinal ligament (PLL) will be seen.

The need to open the PLL is debated. Numerous authors recommend routine opening of the PLL after removal of the dorsal anulus fibrosus.^{42,48,51,73–75} However, others do not agree with the routine sectioning of the PLL after good quality preoperative radiographic imaging studies.^76–78 Although preoperative imaging studies may suggest that the disc material has not protruded dorsally, the PLL may be safely sectioned to allow for entry into the epidural space. On entry a blunt nerve hook may be used to search for disc material. In addition, the PLL itself may be thickened and may be responsible for ongoing neural compression. As a result, if there is any doubt about the adequacy of decompression, the PLL should be opened sharply to allow a direct look at the underlying dura mater. Any disc fragments dorsal to the PLL are removed. Likewise, ridges from dorsal osteophytes may compress the spinal cord or nerve roots. If osteophytes are detected, either by preoperative imaging studies or during the surgical procedure, they should be resected using small Kerrison rongeurs.^{1,7,24,50,76,79–82}

Tearing of the underlying dura mater is possible during the opening of the PLL. This is particularly likely in cases of ossification of the PLL and in patients who have undergone previous ventral procedures.^83,84 In a series of 450 patients who underwent ventral cervical surgery, Bertalanffy and Eggert reported 8 patients (1.8%) who sustained damage to the dural sac. Of these 8 patients, 1 developed meningitis.⁴⁶ If a dural tear occurs, it is usually impossible to repair the defect primarily. The methods used to prevent egress of cerebrospinal fluid (CSF) include placing free muscle and fascial grafts and using Gelfoam soaked in thrombin or fibrin glue. Additionally, newer dural substitutes made from synthetic materials, bovine grafts, and collagen can also be used.^85–88 With a dural tear, placement of a lumbar subarachnoid drain must be considered to divert CSF in the immediate postoperative period. Once the PLL is opened, instead of electrocautery, thrombostatic agents such as Gelfoam and cotton patties should be used for hemostasis. Our philosophy has been to routinely open the PLL in all cases of radiculopathy and myelopathy. In our practice, only surgery for axial mechanical neck pain, which constitutes less than 5% of our cases, is performed without opening the PLL.

The width of the decompression is determined on a case-by-case basis. Care must be taken to maintain the orientation of the midline, which is essential when determining the width of decompression. Useful techniques include referring to the marking of the true bony midline made before the longus colli muscle dissection, as well as being aware of the anatomic bony structures, such as the uncovertebral joints. As a general rule a 15-mm bony dissection centered over the midline is necessary for an adequate decompression.⁸⁹ If nerve root compression is present, the dissection may be extended laterally. The medial border of the uncovertebral joint serves as a bony anatomic marker of the lateral extent of a cervical discectomy. Limiting the dissection to this point will allow for a good decompression of the shoulder of the nerve root. Once again, the majority of intraoperative neurologic injuries that occur are the result of loss of orientation of the bony anatomic midline. A useful intraoperative maneuver to prevent an excessively wide discectomy is frequent placement of a cotton patty in the discectomy defect. A standard cotton patty measures 13 mm and allows for reorientation throughout the procedure.

As mentioned earlier in this chapter, the majority of neurologic injuries occur during the deep portion of the discectomy procedure. The most common complications include dural tears, damage to the neural elements, and vertebral artery injuries. Intraoperative nerve root injuries and spinal cord contusions occur in less than 1% of ACDs.^{2,4,7,16,28,46,90,91}

If the discectomy is too wide, the vertebral artery may be injured. The vertebral artery and its accompanying venous plexus are at risk during removal of the lateral disc material.^{6,8,54,55,92,93} Profuse arterial bleeding occurs after a vertebral artery injury. If the patient’s head was rotated as part of the initial operative positioning, the head should be immediately returned to the midline before attempts are made to control bleeding.⁹⁴ Immediate tamponade should be used for the initial management of vertebral artery injuries. If the tamponade maneuver is unable to curtail bleeding successfully, either direct ligation or primary repair of the vertebral artery may be necessary.⁵⁴ These maneuvers are technically demanding and require extension of the exposure in both a rostral and a caudal direction. More recently, neuroendovascular treatment, performed immediately after a suspected vertebral artery perforation, has been used to successfully treat these injuries.

In patients with two functional vertebral arteries and an intact circle of Willis, the majority of vertebral artery injuries are asymptomatic. As a result, the actual incidence of vertebral artery injuries may be underappreciated. However, if one vertebral artery is thrombosed, or if a hypoplastic artery is present, occlusion of the dominant vertebral artery may be catastrophic.⁸⁴ Shintani and Zervas reviewed the results of 100 patients whose vertebral arteries were ligated for a variety of reasons and found a 12% mortality rate.⁹⁵ A useful note is that each vertebral artery is ordinarily accompanied by one to three paravertebral veins, which are generally located medial to the vertebral arteries. If paravertebral vein bleeding is encountered, hemostasis should be attained, and further lateral dissection should not be attempted.⁹⁴ Injuries to these paravertebral veins are not associated with a postoperative neurologic deficit. The venous bleeding simply serves as a warning that the vertebral artery may be in proximity.

If the discectomy is performed for myelopathy or degenerative disc disease, the width of the discectomy may be more limited. Saunders has stated that a width of 15 mm is adequate for decompression.⁸⁹ However, if nerve root compression is part of the preoperative diagnosis, a wider discectomy on one or both sides may be necessary. When performing the dissection in the lateral portion of the disc space, the use of dissectors such as blunt nerve hooks should limit the possibility of direct nerve root trauma. Nerve root injuries may result from direct trauma or from excessive manipulation of the nerve root during the discectomy. Manipulation of the nerve root is particularly problematic with the C5 nerve root, which appears to be more vulnerable to injury; therefore, extreme care should be taken to avoid manipulating it when performing C4-5 discectomies. If a nerve root injury occurs, there is no effective intraoperative management.⁸⁹ In addition, delayed C5 nerve root palsies have been detected in up to 4% of ventral cervical surgeries regardless of the levels treated. Fortunately, the great majority of these delayed C5 palsies, which are usually apparent a few days after surgery, are completely resolved within 3 to 6 months.

Donor Site Considerations

The skin incision for harvesting an autologous bone graft from the iliac crest should be at least 2 cm lateral to the anterior superior iliac spine. An incision placed medial to this point may result in an injury to the lateral femoral cutaneous nerve. If direct transection of the nerve occurs, permanent numbness in the ventrolateral thigh results. Lateral femoral cutaneous nerve dysfunction may be transient when it occurs secondary to excessive retraction of the nerve.

Numbness of the skin that immediately surrounds the iliac incision is a common finding; it is usually transient. The skin incision should also be placed approximately 0.5 cm below the most prominent edge of the iliac ridge. In this manner the incision does not lie over the iliac crest, thus minimizing irritation from belts and other items. Also the fascial plane between the inner and outer musculature inserting on the iliac crest may be dissected with the least amount of muscle destruction.

Autologous iliac crest bone grafts for ACDF are usually tricortical. When the iliac crest is being exposed for the removal of the bone graft, the medial musculature must be dissected free from the most medial border of the iliac crest. If the transversalis fascia is violated during this medial dissection, a hernia may occur. If this fascial violation is detected intraoperatively, it should be repaired immediately to prevent the hernia.

Tricortical iliac crest bone grafts may be obtained by using an oscillating sagittal saw. The use of an osteotome produces microfractures in the bone graft,⁹⁶ which, as hypothesized by some, may lead to graft collapse. Many surgeons, however, successfully use osteotomes for this purpose.

After the removal of the bone graft, hemostasis is obtained with unipolar electrocautery for soft tissue hemostasis. Frequently, bleeding of the exposed cancellous portion of the iliac crest may occur. This is controlled best by irrigating the wound generously, followed by firmly packing the wound with laparotomy pads soaked in thrombin. The wound is copiously irrigated again. After adequate hemostasis has been obtained, a drain may be placed in the bed of the wound and brought through a separate stab wound in the skin. Foreign bodies, such as bone wax, should be used minimally and only when necessary.

The major complications associated with iliac crest bone graft sites include lateral femoral cutaneous nerve palsies, postoperative hematomas, and postoperative wound infections. Appropriately placed skin incisions should prevent nerve palsies, and good surgical technique should prevent the development of hematomas. The incidence of donor site hematomas ranges from 2%^{3,6,19,35,46,77,97–100} to 7%.^53,65,67,72 Donor site infections may be limited by the use of perioperative antibiotics, generous irrigation, and preventing wound hematoma accumulation. The incidence of donor site infections has been reported to be between 0.2%^* and 5%.^10,77 Finally, it is important to limit the subperiosteal dissection when removing an iliac bone graft, because hematomas may develop in the subperiosteal space and lead to persistent hip pain or meralgia paresthetica. The latter occurs in 0.6% to 5.8%.^{4,6,7,17,19,77}

Attempts have been made to find alternative sites for graft harvest to avoid the complications of iliac crest bone grafts while maintaining the benefits of using autografts.^102–105 Alternative sites include the spine, manubrium, clavicle, and rib. Although some of these results are promising, they are limited by study design and sample size. Until further studies are available, the iliac crest remains the best site for graft harvest.

Fusion

The majority of difficulties with postoperative axial neck pain result from inadequate bony fusion. Regardless of whether the discectomy was performed for myelopathy, radiculopathy, or degenerative disc disease, a solid bony fusion is optimal. Options for interbody fusion substrate include structural autologous iliac crest, structural allograft, titanium, and polyetheretherketone (PEEK) or carbon fiber cages, with or without supplemental nonstructural autograft or allograft. Currently, no class 1 data exist to support the use of one method over another. Class 2 data are available to suggest that autograft, allograft, and titanium cages are all suitable for achieving bony fusion.¹⁰⁶ For a noninstrumented single-level ACDF, a fusion rate of greater than 80% is expected with autograft bone harvested from the iliac crest.^106,107 Similar fusion rates are expected with allograft and interbody cages and avoid the donor site complications from iliac crest bone harvest. In nonimmunocompromised patients who are nonsmokers and who undergo single-level discectomy, long-term fusion rates are high, regardless of the fusion substrate used.^{8,10,27,53,100} In smokers, immunocompromised patients, and patients who undergo multilevel discectomies, autologous bone graft yields the best long-term fusion results.¹⁰¹ Recombinant human bone morphogenetic protein (rhBMP-2) has more recently been used in an off-label fashion for anterior cervical fusions. Numerous reports of increased complication rates related to its use, such as severe postoperative soft-tissue edema, hematoma formation, and dysphagia, have since emerged.^106,108 Consequently, the U.S. Food and Drug Administration released a public health notification advising against the use of rhBMP-2 for anterior cervical fusions.

Autologous bone is an ideal graft because it is osteogenic, osteoinductive, and osteoconductive. To date, no graft substitute is available that possesses all three of these properties. The surgeon must consider both the donor site complications of autologous iliac crest bone graft and the cost and complications of graft substitutes when deciding which to use.

Experience from the treatment of long bone fractures has shown two elements to be of greatest importance in achieving a bony fusion—compression and immobilization. After distraction of the disc space a bone graft that is slightly larger than the nondistracted interspace should be chosen. This allows for the bone graft to be seated under a compressive load. Bone placed under a compressive load will adapt and remodel itself, thus becoming stronger to resist axial loading in accordance with Wolff’s law.¹⁰⁹

Before placement of a bone graft, the recipient site must be meticulously prepared. This includes removal of all articular cartilage from the bony end plates above and below, with care taken to preserve the actual bony end plates. In addition, ventral osteophytes should be resected. The graft should be aligned between the vertebral bodies above and below so that the cancellous portion of the vertebral body is in direct alignment with the cancellous portion of the bone graft proper. Before placing the bone graft, single small perforations of the vertebral body end plates above and below with a high-speed drill allow for exposure of bleeding cancellous bone while not compromising the peripheral portion of the end plates that are in contact with the cortical bone of the graft or with the cages. These end-plate perforations should be aligned with the cancellous portion of the iliac bone graft.

A slightly oversized bone graft should be centered over the midline with a minimum width of 10 mm (Fig. 40-3). The depth of the bone graft should be determined by a careful review of the preoperative imaging studies, and it should be confirmed by intraoperative visual inspection. In general, bone graft depth should measure between 12 and 15 mm.

FIGURE 40-3. Sagittal MRI of a 54-year-old female who presented with complaints of axial neck pain and progressive myelopathy, demonstrating multilevel cervical kyphosis and herniated intervertebral discs at the C3-4, C4-5, C5-6, and C6-7 levels with spinal cord compression (A). Immediate postoperative anteroposterior (B) and lateral (C) radiographs following the performance of four-level ACDFs from C3 to C7. Note that the screw-plate system is centered on the midline, with screw trajectories passing through the center of the vertebral bodies. Screw trajectories for the rostralmost and caudalmost levels are angled superiorly and inferiorly, respectively, to maximize screw purchase at the extremes of the construct. Cervical lordosis has been restored by lordotically shaped interbody autografts at each level and the use of a lordotically contoured plate. The plate sits flush with the ventral surface of the vertebral bodies and the interbody grafts are countersunk by 1 mm below the ventral surface of the vertebral bodies. Coronally reconstructed CT scan (D) of the same patient at short-term follow-up demonstrating the midline position of the interbody grafts and screws. Screw trajectories through the center of the vertebral bodies are demonstrated.

The bone graft is oriented with the open end of the tricortical graft directed dorsally (Fig. 40-4). This allows maximum cortical bone at the most ventral aspect to provide a stable strut ventrally, thereby minimizing kyphotic angular deformation. The bone graft should be gently impacted into place and countersunk so that the most ventral aspect of the bone graft is 1 mm below the most ventral surface of the vertebral bodies above and below. Attempts to reduce segmented kyphotic deformation or preserve normal lordotic posture should be aggressive. Kyphotic deformities predispose to further degenerative changes at adjacent levels. With an increased appreciation of the benefits of preserving or improving cervical sagittal plane alignment, we routinely sculpt our graft in a lordotic fashion so that the ventral height of the graft is approximately 2 mm longer than the dorsal graft height.

FIGURE 40-4. Early postoperative sagittally reconstructed CT scan following three-level anterior cervical discectomy and fusions from C4 to C7. The open end of the tricortical autograft is directed dorsally, and the ventral aspect is countersunk 1 mm below the ventral vertebral body surface. Screw trajectories are directed superiorly and inferiorly at the rostral and caudal extremes of the construct, respectively. The plate sits flush with the ventral aspect of the vertebral bodies and is lordotically contoured to allow for maintenance of a normal sagittal alignment of the cervical spine.

After the graft is placed, a blunt nerve hook should be used to confirm that the graft is not seated too deeply. If the bone graft is seated too deeply or too far lateral, the spinal cord or nerve roots may be compressed. If this is identified intraoperatively, the graft should be removed and either replaced or modified to fit the interspace accordingly. After the bone graft is in place, the interbody distraction device is removed. A lateral cervical spine radiograph is obtained, with distraction pins in place, to confirm correct graft placement and spine alignment and to determine the optimal screw length if a screw-plate stabilization construct is to be placed. Proper screw length is determined by examining the radiographic appearance of the known distraction pin screw lengths.

If multiple interbody fusions are to be performed, the interbody distractors are then placed sequentially at each level and the interbody graft is placed. After placement of all interbody grafts, all distraction devices and pins are removed, all traction is discontinued, and a lateral cervical radiograph is obtained. The radiograph should be studied to confirm spine alignment and the depth of the bone graft(s) and to reconfirm that the facet joints are not overdistracted (Fig. 40-5A).

FIGURE 40-5. A noninstrumented anterior cervical discectomy and fusion at C6-7 with a generous, oversized bone graft with the crest portions of the graft oriented ventrally. A, Note that the graft is seated 2 mm below the ventral-most surface of the vertebral bodies above and below. B, A subsequent radiograph (3 months postoperatively) demonstrates an acceptable degree of subsidence.

Ventral cervical plating is now often employed when performing ACDF. The potential benefits of plating include higher fusion rates, decreased pseudarthrosis and strut graft dislodgement, resistance to segmental kyphosis, and less need for external immobilization. A recent meta-analysis suggests that ventral plating increases fusion rates regardless of the number of levels involved.¹⁰⁷

When using ventral cervical plating the basic technique is as follows: proper identification of the midline and the alignment of the plate along its centerline, meticulous preparation of the ventral vertebral bodies to facilitate plate contact, selection of a properly sized plate, selection of a screw size that provides maximal cortical purchase based on preoperative or intraoperative imaging, screw placement within the vertebral body, and engaging the screw-plate locking mechanism (see Fig. 40-3). The exact plating system chosen will determine any variations to screw placement.

It is important for the rostral end of the plate system to sit as flush as possible with the ventral vertebral bodies. This is accomplished through meticulous preparation of the ventral vertebral bodies to accommodate the plating system, in addition to the specific technique used to place the screw-plate system. Once the centerline of the plate is aligned with the midline and the correctly sized plate is chosen, which will allow screws to be placed in the vertical center of the vertebral bodies to be fused, the first screw hole is drilled at the caudalmost level on the surgeon’s side. A self-tapping screw is then placed and tightened until approximately 90% of the screw threads are engaged within the vertebral body. The two rostralmost screw holes are then drilled, the screws are placed, and the screws are fully engaged within the vertebral body to allow the plate to sit as flush as possible at its rostral end. The caudal screw is then fully engaged and a screw is placed on the contralateral side of the caudally fixated vertebra. If a multilevel fusion is being performed, screws may then be placed at each intermediate level to achieve additional points of fixation. A final lateral radiograph is obtained to confirm graft position, screw-plate position, spine alignment, and the appearance of the dorsal facet complexes. After this confirmatory radiograph is obtained, the final locking mechanism of the plate is engaged. Once again, it is essential to release the distraction pins or the tongs before placing the spinal instrumentation to prevent inadvertent loading of the instrumentation with stress shielding of the bone graft or cage.

The most common complication of the fusion portion of the operation is the development of a delayed nonunion, or pseudarthrosis. Complications related to improper positioning of the bone graft are less common. Useful intraoperative maneuvers to avoid nonunion include placement of the graft under tension and the use of an adequately sized bone graft. Preservation of the vertebral body end plates above and below minimizes the chance of collapse or pistoning (Fig. 40-5B). Graft collapse has been detected on follow-up imaging studies in 0.8% to 5.8% of cases.^{17,27,65,77,100,110} Foreign bodies should be avoided at all times. Bone wax limits bony fusion rates and should be avoided.

After the bone graft is placed, hemostasis must be attained. Generous irrigation is performed. A drain may be placed in the prevertebral space, ventral to the bone graft, and it is brought out through a separate stab wound in the skin. However, as with the iliac donor site, drains are not mandatory.

Complications

Postoperative complications are categorized as problems related to the decompression (neurologic) and those related to the fusion (pain). In the immediate postoperative period, neurologic complications are the most common. Overall, complications include esophageal injury, postoperative airway compromise, vertebral artery injury, dural tear, spinal cord injury, dysphagia, dysphonia, graft dislodgement, infection, and hematoma.^30,38,111

The most catastrophic immediate postoperative complication is the development of an epidural hematoma, with an accompanying neurologic dysfunction. Symptomatic epidural hematomas occur in 0.2% to 0.9% of cases.^{2,46,55,75,92} This complication is managed by immediate surgical evacuation of the hematoma. Any unnecessary delay in the evacuation of an epidural hematoma may lead to an irreversible neurologic deficit. If a postoperative neurologic decline that suggests an epidural hematoma is observed, either a CT scan and a myelogram or an MRI study should be performed immediately. Alternatively, if a high index of suspicion suggests the presence of spinal cord compression, the patient can be brought back to the operating room immediately without advanced neuroimaging studies being obtained.

If an epidural hematoma is identified on postoperative neuroimaging, the patient is immediately returned to the operating room, the bone graft is removed, and the hematoma is evacuated. If there is no evidence of compression of neural tissue on the neuroimaging study, expectant observation is proper. In the absence of imaging evidence of neural compression, the majority of neurologic deficits resolve.

An additional complication during the postoperative period is an unrecognized dural tear. If this occurs, a lumbar drain is placed and maintained for 1 week to divert the flow of CSF and allow the durotomy to spontaneously close. If this is unsuccessful, surgical reexploration and direct operative treatment of the durotomy may be necessary.

Wound infections may occur at variable periods during the postoperative course. These are best identified by persistent pain, as well as by an elevation of the erythrocyte sedimentation rate. Fever or an elevated white blood cell count is not a reliable indicator of postoperative wound infections. Wound infections occur in 0.1% to 2% of cases.^* If a cervical wound infection is identified, the treatment is prompt surgical reexploration, culture, irrigation, and closure of the wound, with the placement of a drain. Appropriate antibiotics are used postoperatively. If an iliac crest wound infection occurs, the wound must be reopened, debrided, and drained. Prevention of cervical and iliac crest wound infections is best accomplished by avoiding the use of foreign bodies (e.g., bone wax) and by obtaining meticulous hemostasis. Some surgeons argue that the use of drains may decrease the development of hematomas and subsequently decrease wound infection rates. Others argue that they provide an access route for microorganisms.

Iliac region pain is ordinarily secondary to the development of a subperiosteal hematoma. The majority of these resolve spontaneously. If the hematoma is excessively large or painful, surgical reexploration and evacuation of the hematoma may be necessary. Persistent occult blood loss during the postoperative period may be secondary to enlargement of a retroperitoneal hematoma. This may dictate the need for reexploration of the iliac crest graft harvest site. A wound infection must also be ruled out. In questionable situations, obtaining a bone scan and a C-reactive protein level may be helpful in establishing the diagnosis. A postoperative hernia secondary to violation of the transversalis fascia may present with chronic donor site pain postoperatively. This may be diagnosed by an intraluminal contrast study such as a barium enema. If a painful hernia is present or if a bowel obstruction occurs, surgical reexploration, with closure of the hernia defect, is usually successful.

Postoperative neck pain in the first few weeks is usually transient and self-limited. Persistent postoperative pain in the neck, arm, and interscapular region has been observed in 4% to 20% of cases.^{7,46,48,80,97} Wound infections or the development of a deep hematoma should be ruled out. We have found that surgery at the C6-7 level is most frequently associated with postoperative interscapular pain. Fortunately, this pain is usually transient.

A bony nonunion, or pseudarthrosis, after an ACDF often presents with persistent axial neck pain. This may or may not be associated with radicular symptoms. Bony fusion is typically well under way by 12 weeks postoperatively. This may be delayed in smokers, immunocompromised patients, or patients undergoing multilevel discectomies. A pseudarthrosis is diagnosed by persistent axial neck pain with evidence of a radiographic lucency at the vertebral body–graft junction at 6 or more months after surgery. Bone graft collapse is diagnosed by a 2-mm or greater loss of graft height detected on radiographs taken 12 months postoperatively.³⁵

If a pseudarthrosis develops, imaging studies should be performed to confirm whether neural compression is also present. If neural compression is present, a repeat ventral operation is necessary to remove the bone graft, perform a neural element decompression, and re-fuse the cervical spine. If axial neck pain is present and neuroimaging studies do not demonstrate evidence of neural compression, a cervical pseudarthrosis is best treated with either a ventral or dorsal fusion of the involved motion segment. A successful dorsal fusion for the treatment of a pseudarthrosis secondary to an ACDF most often results in a stable circumferential fusion. In exceptional cases it may be necessary to revise a pseudarthrosis ventrally and perform a dorsal fusion at the same time. This leads to a higher fusion rate, but is considered excessive by some.

If the patient develops persistent axial neck pain and plain radiographs cannot demonstrate a lucency suggestive of a pseudarthrosis, further diagnostic studies may be necessary. Tomograms are more sensitive than plain radiographs for detecting pseudarthroses. In addition, flexion and extension views may help confirm the diagnosis. CT scans with sagittal reconstructions are very effective at identifying nonunions.

The issue of postoperative immobilization is controversial. Some authors use no postoperative bracing after a single-level ACDF. Others use a cervical collar for a variable period of 6 to 12 weeks. In rare circumstances, a postoperative Minerva jacket or halo vest may be used for prolonged immobilization. A spinal implant may be indicated in a patient who is likely to suffer fusion failure. Such patients include smokers, immunocompromised patients, and those undergoing multilevel discectomies.

In the postoperative period, serial radiographs are obtained until a bony fusion is confirmed. Patients should be followed for a minimum of 12 months postoperatively and should only be discharged after evidence of a successful clinical and radiographic fusion. We typically discontinue patient follow-up after 24 months in patients with good outcomes.

Other delayed complications that may occur after an ACDF include a loss of cervical lordosis. This is most commonly observed after the use of undersized grafts, graft material of insufficient integrity, or excessive end plate removal, possibly leading to the development of a kyphotic deformity (Fig. 40-6).^2,57,100,110 In general, no surgical intervention is necessary for this problem, unless it is severe. Graft subsidence without angulation may also occur.

FIGURE 40-6. Graft collapse with kyphotic angulation is seen in this noninstrumented C5-6 anterior cervical discectomy and fusion 3 months after surgery. This collapse is frequently the result of excessive removal of the bony vertebral end plates or an undersized graft.

Some neck motion is lost postoperatively. As a general approximation, there is a 10-degree loss of cervical motion for each fused motion segment. For a single-level discectomy this loss of motion is not ordinarily discernible. With multilevel discectomies the patient and physician may notice a loss of neck motion.

Graft protrusions or dislodgements occur in 0.4% to 4.6% of cases.^* The treatment of a graft dislodgement involves a surgical reexploration and fusion.

Discitis or osteomyelitis may also occur as a delayed complication.^{1,24,46,57,65,66,77} This warrants antibiotic therapy and, usually, surgical debridement.

Some patients (as many as 50%) develop persistent radiographic nonunion without clinical symptoms. Lateral radiographs from these patients have a persistent lucency, but no clinical neck pain or radicular symptoms. Such patients should be followed clinically with serial imaging studies. Delayed radiographic fusion may occur in some of these cases. If radiographic fusion is not demonstrable but no clinical symptoms are present, there is no indication for surgical reexploration.

After an ACDF, there is an increased risk of disc degeneration at the levels adjacent to the fused segments (accelerated degenerative changes or adjacent segment disease). This is most common and is clinically significant at the interspace immediately rostral to the fusion. Adjacent-level disc degenerations may occur after longer cervical fusions, and longer-term follow-up is necessary after a multiple-level ACDF, both to monitor the fusion itself and to monitor for degenerative changes at adjacent levels. Adjacent-segment disease may require treatment if symptomatic.

Accelerated degenerative changes at motion segments adjacent to a spine fusion may occur as a result of increased biomechanical stresses and hypermobility. Some surgeons have advocated the performance of a total disc arthroplasty (TDA) in an off-label fashion, for the treatment of adjacent-segment disease, as a well-intentioned effort to preserve motion at the affected spine level. However, since the pathophysiology of adjacent-segment disease is hypermobility itself, we recommend an ACDF rather than a “mobility-sparing” TDA (Fig. 40-7). In addition, we strongly recommend the use of autograft in this clinical scenario because a more rapid spine fusion is likely to be obtained, and thus there will be a shorter time in which the screw-plate construct is exposed to the increased biomechanical stresses at this excessively mobile spine level.

FIGURE 40-7. A, Sagittally reconstructed CT scan of a 48-year-old female who previously underwent three-level anterior cervical discectomy and fusions from C4 to C7. After 3 years, a herniated disc at C3-4 was treated by a total disc arthroscopy (TDA) with the Prodisc device for adjacent-segment disease. The goal of this total disc arthroscopy was to preserve motion at that adjacent level; however, immediately after the TDA, the patient developed severe axial neck pain that was unresponsive to conservative treatment. A reoperation was performed to remove the TDA and stabilize and fuse the unstable segment. Due to the keel on the device and rigid incorporation of the TDA at the TDA-C4 surface, a C4 corpectomy was necessary for its removal. B, The previously placed polyetheretherketone cage at C4-5 was also removed and structural autograft was placed from C3 to C5. The TDA had not incorporated into the inferior C3 bony end plate, and it was removed from C3 without substantial damage to the C3 end plate. The patient experienced immediate relief of axial neck pain in the early postoperative period. C, Lateral cervical spine radiograph at 1-year follow-up, demonstrating full incorporation of the bone graft and fusion from C3 to C7. Improved spinal sagittal alignment was obtained, and graft position remains optimal.

Hospitalization for ACDF can range from less than 24 hours to 3 to 4 days. Given the low overall complication rate of ACDF, it seems feasible that this surgery could be performed on an outpatient basis. Doing so could significantly lower the cost of performing this procedure. Although class 1 data on this topic are lacking, recent studies have attempted to evaluate the safety of performing outpatient ACDF.^113–115 The results of these studies suggest that this surgery can be safely performed on outpatients with a short observational period. Until further studies are available, the surgeon must continue to evaluate the preoperative, intraoperative, and immediate postoperative considerations when deciding the length of hospitalization for patients.

Multiple-Level Anterior Cervical Discectomy and Fusion

The complications associated with multiple-level discectomies and fusions are similar to those for single-level operations, with respect to each fused segment. However, certain complications are more prevalent with multiple-level operations. The rate of pseudarthrosis increases with the addition of each fused segment.^{8,10,27,53,86,100,102,116–118} Thus, the indication for each fused level must remain as strict as the indications for a single fused level. Dysphagia rates are higher because of the longer duration of surgery with prolonged retraction of the esophagus. Similarly, the incidence of hoarseness secondary to RLN dysfunction is higher with multiple-level discectomies. This is particularly true if the C6-7 space is fused. Multiple-level discectomies require a longer operative time, which increases the complications related to anesthesia, as well as general medical problems. In addition, larger iliac crest bone grafts are necessary for multiple-level discectomies. The incidence of bleeding, pain, and infections at the iliac crest donor site may thus be increased. The strategies for avoiding and managing each of the individual complications are identical for multiple-level and single-level discectomies.