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, with the increasing recognition of the importance of normal lordotic cervical sagittal alignment on surgical outcomes, every attempt should be made to maintain, and preferably improve, cervical lordosis ( Fig. 59-1 ). 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.

Lateral ( A ), flexion ( B ), and extension ( C ) radiographs of a C5-6 fixation. Solid fusion with bridging trabecular bone and no motion of the spinous processes between flexion and extension can be seen. The C2-7 Cobb angle remained normal postoperatively.

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 if this region will be utilized to obtain bone graft material. 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 Apfelbaum and colleagues 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. This vulnerability is particularly true with lower cervical dissections ( Fig. 59-2 ). The reported incidence of postoperative RLN palsies presenting as postoperative hoarseness varies between 0.8% and 9.6%. 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 spine ( Fig. 59-3 ). 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 theoretic risk of pneumothorax or mediastinitis with approaches from either side.

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, Albuquerque.)

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

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

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, and 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 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 has been 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. 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.

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% and 5%. Esophageal perforation has also been reported in cervical discectomies. 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, a colored inert dye, such as methylene blue or indigo carmine, should be instilled to assist with demonstration of the violation. Unrecognized esophageal perforations can lead to the development of deep soft tissue infections (including mediastinitis). These may manifest as Mackler’s triad of vomiting, severe retrosternal pain, and subcutaneous emphysema. Other severe complications of esophageal perforation include esophagocutaneous fistula and even death.

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.

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 into 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 too widely, a Horner syndrome—the triad of ipsilateral ptosis, myosis, and anhidrosis—may result. The incidence of postoperative Horner syndrome varies from 0.1% to 2% 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. This 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. 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. Dysphagia rates have been reported to vary from 1.8% to 9.5%, to between 21.2% and 35%. 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 reinflation to the lowest pressure that eliminates air leak, confirms that the vocal cords are not being excessively compressed.

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 headlight 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 hemostatic gelatin (Gelfoam), soaked in thrombin, and cotton patties. After removal of the anulus fibrosus, the underlying posterior longitudinal ligament (PLL) will be visible.

The need to open the PLL has been debated. Numerous authors have recommended routine opening of the PLL after removal of the dorsal anulus fibrosus. However, others do not agree with the routine sectioning of the PLL after good quality preoperative radiographic imaging studies. 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.

Tearing of the underlying dura mater is possible during the opening of the PLL. This is particularly likely in cases of opacification of the posterior longitudinal ligament (OPLL) and in patients who have undergone previous ventral procedures. 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. If a dural tear occurs, and is noted intraoperatively, primary repair should be attempted. Postoperatively, the head of the bed is kept at 30 to 45 degrees for a minimum of 48 hours. Additional surgical techniques that may be employed to prevent egress of cerebrospinal fluid (CSF) include placing free muscle and fascial grafts and using Gelfoam soaked in thrombin or fibrin glue. Newer dural substitutes made from synthetic materials, bovine grafts, and collagen can also be used. If CSF leakage continues, placement of a lumbar subarachnoid drain should be considered to divert CSF for 3 days postoperatively. After this, if signs of CSF leakage continue, the decision to reopen to attempt primary repair or placement of a ventriculoperitoneal shunt can be considered. 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. 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 a loss of orientation of the bony anatomic midline. A useful intraoperative maneuver to prevent an excessively wide discectomy is placement of a cotton patty in the discectomy defect. A standard cotton patty measures 12.5 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.

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. 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. 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. 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 address 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. 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. 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. 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. 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 the C5 nerve root when performing C4-5 discectomies. If a nerve root injury occurs, there is no effective intraoperative management. In addition, delayed C5 nerve root palsies have been reported to occur in 1.6% to 12.1% of anterior cases, with an increasing number of levels and corpectomies correlating to increased incidences. Fortunately, the great majority of these delayed C5 palsies, which are usually apparent a few days after surgery, are completely resolved within 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 injure the lateral femoral cutaneous nerve. If direct transection of the nerve occurs, permanent numbness in the ventrolateral thigh may result. Lateral femoral cutaneous nerve dysfunction may be transient when it occurs secondary to retraction of the nerve.

Numbness of the skin that immediately surrounds the iliac incision is a common finding, and 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, which minimizes 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 can produce microfractures in the bone graft, 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 monopolar 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. We have preferred to utilize a Gelfoam paste formed by a combination of Gelfoam powder and thrombin to pack into the exposed cancellous bone to aid in hemostasis.

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% to 7%. 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 7.5%. 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% of cases.

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. 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 optimal 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 necessary to achieve the best postoperative result. 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, PEEK, carbon fiber, and titanium cages are all suitable for achieving bony fusion. For a noninstrumented single-level ACDF, a fusion rate of greater than 80% is expected with autograft bone harvested from the iliac crest. 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. In smokers, immunocompromised patients, and patients who undergo multilevel discectomies, autologous bone grafts yield the best long-term fusion results. Recombinant human bone morphogenetic protein (rhBMP-2) has 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 protracted dysphagia, have emerged. Consequently, the U.S. Food and Drug Administration (FDA) 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 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. In accordance with Wolff’s law, bone placed under a compressive load will adapt and remodel itself, thus becoming stronger to resist axial loading.

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 placement of the bone graft, a high-speed drill is used to make single small perforations of the vertebral body end plates, above and below, which exposes bleeding cancellous bone without 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. 59-4 ). 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 mm and 15 mm.

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

Anatomy of Nerve Root Compression, Nerve Root Tethering, and Spinal Instability Ventral and Ventrolateral Subaxial Decompression Complex Lumbosacropelvic Fixation Techniques Timing of Surgery Following Spinal Cord Injury Spinal Wound Closure Explant Analysis of Wear, Degradation, and Fatigue in Motion Preserving Spinal Implants

Stay updated, free articles. Join our Telegram channel

Join