Historical Perspective

At the turn of the 20th century, Elliot first reported how arthritis in the cervical spine appeared to be responsible for the development of radicular symptoms caused by compression at the neural foramina.³ Stookey later revealed pathologic syndromes caused by cervical disk herniations that were incorrectly attributed to chondromas.⁴ Stookey divided the compression of these extradural chondromas into three regions: (1) those compressing half of the ventral aspect of the spinal cord, (2) those compressing both halves of the spinal cord, and (3) those compressing laterally on the nerve roots. Elsberg classified these chondroma-like lesions as ecchondrosis and local hyperplasia of the cartilage.⁵ Stookey and Elsberg were the first surgeons to address the surgical removal of chronic degenerated cervical disks. The classic paper by Mixter and Barr first presented the correlation between radicular symptoms and lateral herniation of the lumbar disks.⁶ This observation propelled an intense interest in the role of cervical disk degeneration and herniation in the development of cervical radiculopathy and myelopathy.

The surgical approach to the treatment of cervical disk disease was refined in the 20th century. In 1955, Smith and Robinson described their anterior approach for removing the disk and performing an arthrodesis with a horseshoe-shaped bone graft⁷ and later expanded the success of this technique.^8,9 In 1958, Cloward presented his technique for removing the disk and performing an interbody fusion with a cylindrical bone graft.¹⁰ In 1960, Bailey and Badgley introduced interbody fusion through a keystone technique.¹¹ In the late 1960s, Verbiest expanded the anterior approach to incorporate a more anterolateral exposure for resecting the foramen transversarium and controlling the vertebral artery.¹² These procedures have enjoyed a tremendous amount of success in the treatment of cervical spondylosis and degenerative disk disease. The advent of new imaging modalities has further improved understanding of the natural history of cervical spondylosis. Moreover, new spinal instrumentation permits safe and extensive decompression with excellent clinical outcomes.

Cervical Spine Anatomy

The cervical segment of the spine consists of seven vertebrae. Within the cervical spine, there are three distinct anatomic, physiologic, and biomechanical regions. Because the cervical vertebrae bear the least weight of any spinal region, the cervical vertebral bodies are small in relation to their respective arch and transverse foramina. In addition, the transverse diameter is greater than the anteroposterior (AP) diameter. Except for the upper two cervical vertebrae, each vertebra articulates with adjoining vertebrae at the intervertebral disk interspace and at the facet joints posteriorly. The disks are wider anteriorly than posteriorly, and this configuration creates a natural lordotic posture. Within the intervertebral space, the superior surfaces of the vertebrae turn sharply upward in a superolateral direction to form the uncinate processes.

A unique feature of the cervical vertebrae is the transverse foramen, which perforates the transverse processes. The anterior aspect of the transverse process represents a fused costal joint that arises from the vertebral body. The lateral portion of the transverse process contains two projections referred to as the anterior and posterior tubercles. The anterior tubercle serves as the origin of the anterior cervical musculature, whereas the posterior tubercle serves as the origin and insertion of the posterior musculature. The spinal nerves exit through a deep groove within the tubercles. As it traverses from C6 to the skull base, the vertebral artery is located anterior to the spinal nerve roots.

The articulation between vertebral bodies is formed by the disks. Intervertebral disks consist of a semifluid gelatinous matrix, the nucleus pulposus, surrounded by the annulus fibrosus. The intervertebral disk adheres firmly to the vertebral bodies via the cartilaginous end plate. More posteriorly, the position of the nucleus pulposus is slightly eccentric. In younger age groups, the nucleus pulposus has a high water content. With time, however, it dehydrates, thereby leading to degeneration. The annulus fibrosus consists of well-defined fibrous lamellae that adhere strongly to the vertebral end plate. In addition to containing the nucleus pulposus, the annulus fibrosus withstands considerable shearing and tensile forces from all directions. The annulus fibrosus is innervated by the sinuvertebral nerve, which might play a role in the origin of diskogenic pain.¹³

The intervertebral disk is supported by the anterior longitudinal ligament and the posterior longitudinal ligament (PLL). The former is stronger than the latter. The PLL is formed by two bands of fibers. The superficial fibers extend through several vertebral bodies and are attached to their posterior midline. A deeper band extends no more than two vertebral segments and attaches itself firmly into the disks. Laterally, the PLL becomes thinner and does not extend completely to the lateral margins of the disk. These features make this region more susceptible to disk herniation. Lateral disk herniations can compress the exiting nerve roots and cause radiculopathy. Central compression of the spinal cord can occur with central disk herniation and the concomitant development of osteophytes from adjacent vertebral bodies. In some cases, multisegmental ossification of the PLL can also cause severe spinal cord compression.

Biomechanics

Within the cervical spine, several functional regions are responsible for motion. Approximately 40% of axial rotation occurs at the atlantoaxial joints. The anatomic configuration of the atlantoaxial joint, which is stabilized by the transverse and alar ligaments, permits only rotation. The remaining axial rotation is evenly distributed among the subaxial vertebrae, but the middle and lower (C4-7) segments provide the most motion, partially because of the orientation of their facets. Almost 30% to 50% of flexion occurs at the occipital-C2 region; the remainder is distributed unevenly throughout the spine, with the lower cervical segments being mostly responsible.¹⁴

The height of the intervertebral disk accounts for about one fourth of the total height of the cervical spine. The lenticular shape of the disk in the sagittal dimension permits the disk to slide forward. The superior vertebral body overrides the inferior one to increase flexion. Cervical lateral flexion is partially limited by the large pars articularis, intertransverse ligaments, and orientation of the facets. During lateral flexion, considerable coupling related to the horizontal orientation of the facets provides lateral support and increases lateral rigidity. The anatomic configuration of the facet in conjunction with large lateral masses makes hyperextension injuries associated with slight head rotation devastating.

Pathophysiology: the Degenerative Process

Most reports on the natural history of cervical spondylosis and myelopathy were published before the advent of contemporary imaging techniques and do not accurately represent the true natural history of cervical spondylosis.^15–21 New imaging techniques, however, are improving our understanding of the natural history and progression of symptomatic cervical spondylosis and its pathophysiology. Gore and coauthors¹ reported that the radiographic incidence of cervical spondylosis in asymptomatic patients was about 95% in men and 70% in women in the seventh decade of life.

In 1963, Lees and Turner reported their data on a group of patients suffering from cervical stenosis with and without myelopathy.¹⁸ They found that the development of symptoms was typically followed by periods of improvement or stabilization. Of the 44 patients with myelopathy, only 5 showed progressive symptoms at the time of last follow-up. In contrast, in 1967 Symon and Lavender reported that 67% of their patients with conservatively treated cervical myelopathy had a steadily progressive course.²²

More recent studies have also described a more worrisome course for cervical myelopathy. Shimomura and associates observed 56 patients after nonsurgical treatment of cervical spondylotic myelopathy as defined by a Japanese Orthopedic Association score of 13 or higher.²³ Although most patients remained stable, 11 deteriorated and suffered moderate or severe symptoms. In contrast to partial compression, circumferential compression of the spinal cord was predictive of deterioration.

The onset of symptoms is generally in the sixth decade, and men are affected more than women. C5-6 and C6-7 are the levels most involved because of their relatively extensive range of motion. The onset of symptoms is usually insidious, with long periods of stabilization and intermittent episodes of decline. The outcome of symptomatic cervical spondylosis depends on the severity of the radiculopathy and myelopathic signs and the age of patients when they seek treatment.^15,16,19,21

The development of cervical spondylosis is a consequence of disk degeneration and dynamic processes. The vertebrae of the cervical spine contain five joints: two zygapophyseal (facets) joints, two neurocentral (Luschka) joints, and the intervertebral disk. As mentioned, the anatomic configuration of the facet joints allows a significant degree of motion in flexion and extension and some lateral bending. Moreover, the shape of the intervertebral disk in conjunction with its interface with the end plates of the adjacent vertebra permits flexion, extension, lateral bending, and shearing motion. The neurocentral joints are located laterally. They confine the intervertebral disk and closely abut the superior end plate of the adjacent vertebral body with little cushioning. Progressive degeneration of these joints leads to compression of the exiting nerve root and clinical symptoms of radiculopathy.

The anatomy of the cervical spine and its relationship to the neural elements are unique in comparison to other regions of the spine. The cross-sectional area of the cervical spinal canal is almost entirely occupied by the spinal cord and exiting nerve roots. In contrast, the lumbar region is mostly occupied by nerve roots. This anatomic relationship, coupled with increasing cervical motion, makes the cervical spine vulnerable to small degenerative changes that might become manifested clinically.^24,25

Degeneration of any disk is a dynamic process that begins with loss of the absorptive and viscoelastic properties as a result of dehydration and changes in proteoglycans. Events that increase motion, chronic heavy use, and smoking can accelerate these degenerative changes. Disk dehydration alters the biomechanical properties. The resulting loss of height and annular bulging make the disk and end plates more vulnerable to injury. Altered physical demands on the disk produce gradual fibrocartilaginous changes that blur the boundaries between the nucleus pulposus and the annulus fibrosus until they are indistinguishable. Moreover, these biomechanical changes can increase segmental motion and thereby accelerate the degeneration.

As degeneration ensues, fissures in the annulus make the disk more susceptible to herniation and narrow its height. As the disk narrows, the facet joints override each other, and the neurocentral joints rub against the superior end plates. Reparative efforts between adjacent end plates and the joints cause sclerosis of subchondral bone and the formation of osteophytes. As the extent of contact surfaces and the transfer of force to equilibrate the new biomechanical demands increase, the surfaces expand and form disk-osteophyte complexes that constrict the neural foramen and spinal canal.^19,25–27

Unlike the lumbar nerve roots, which exit the foramen after a long oblique course, the cervical nerve roots exit through the neural foramen in a shorter, more direct transverse route. Moreover, the cervical neural foramen is mostly filled by the nerve root. These features make it difficult for the nerve roots to accommodate a decrease in the surface area of their foraminal exit. Consequently, clinical radiculopathy can be associated with an insignificantly small to moderately sized bone spur. Another potential cause of a disk-osteophyte complex is calcified herniated disk material.²⁸ Overt trauma might exacerbate the symptoms of cervical spondylosis; however, its association with the development of cervical spondylosis has not been clearly established.²⁹

As a degenerating disk fails biomechanically, load shared by the facets increases. Together with the ligamentum flavum, these structures become hypertrophied, thus further compromising the spinal canal posteriorly and the neural foramen.³⁰ As the facet joints degenerate, this region becomes incompetent to shear stress, thereby leading to spondylolisthesis or retrolisthesis. Posterior disk-osteophyte complexes form from the inferior articular joint and may further constrict the dimensions of the intervertebral foramen and cause clinical symptoms.³¹ Occasionally, disk-osteophyte complexes become quite large and yet are clinically silent. However, in individuals with congenital cervical stenosis, relatively small osteophytes can compromise a large percentage of the spinal canal and produce significant clinical findings. In patients with spinal canals larger than 13 mm in the AP dimension, symptomatic cervical myelopathy rarely develops.^32,33

In addition to anatomic constraints, the area of the cervical canal changes during flexion and extension.^30,34 During flexion, the spinal cord lengthens and bows anteriorly such that it abuts the posterior surfaces of the vertebral column.³⁵ In the presence of a posteriorly displaced osteophytic complex, the spinal cord stretches over these bars. As documented in autopsy studies, chronic changes develop.^30,35 Local changes in areas of significant compression might affect the physiologic state of local neurons or axons via compressive forces or vascular compromise (venous or arterial).^30,32,36

During extension, the posterior elements become a critical factor in the development of cervical stenosis. Extension of the cervical spine allows the ligamentum flavum to buckle inward and shortens the cross-sectional area available for the spinal cord. The spinal cord also shortens during extension, which increases its cross-sectional area and further compromises the cervical canal.^32,37 In patients with degenerated disks, loss of height, disk-osteophyte complexes, and hypertrophied joints, as seen in older adults, extension injuries can be neurologically devastating.³⁸

The overriding hypertrophied facets narrow the foramen and impale the exiting nerve roots. The size of the foramen can be further compromised by lateral bending and flexion, which causes radicular symptoms.³²

The critical size of the spinal canal and foramen responsible for clinical symptoms is difficult to characterize with current imaging modalities. Individual anatomic and local biomechanical factors are responsible for the development of these symptoms and must be evaluated carefully on an individual basis.^30,39 Excessive motion can cause ligamentous laxity and segmental instability and thereby contribute to myelopathic symptoms. The ligaments become incompetent and hypertrophied, and this condition is usually seen adjacent to surgically or degenerated fused levels. Excessive segmental loading results in degenerative subluxation, which further compromises the spinal canal.²⁹

The actual pathophysiologic mechanism of myelopathy is not fully understood. Proposed theories include direct compression of the neural elements, ischemia from compromise of the vasculature, and repetitive microtrauma to the spinal cord with neck movements. The actual mechanism is probably a combination of direct microtrauma and vascular compromise. A study using a canine model of chronic cervical compression showed the characteristic irreversible pathologic findings of large motor neuron loss, necrosis, and cavitation in the region of the anterolateral gray matter at the level of greatest compression.⁴⁰ There were also potentially reversible changes such as edema and demyelination. The authors postulated that changes in the dimensions of the spinal cord and canal in response to movement pinches the cord when the neck is in certain positions. The pinching then interferes with the microvasculature and causes ischemia in watershed areas.

Clinical Manifestations

Clinical symptoms of cervical spondylosis can develop in an insidious fashion and may include myelopathy, axial neck pain, occipital pain, shoulder pain, and radiculopathy. Myelopathic patients typically exhibit subtle changes in their gait, which tends to be broad-based, stumbling, spastic, and ataxic. Patients report difficulty going up an incline, buckling of their legs, and sensory disturbances in their proximal extremities. They may also report profound weakness and clumsiness of their hands, difficulty with writing and joint position sense, fine tremor, chronic and ill-defined numbness, and intrinsic musculature dysfunction. Bowel or bladder dysfunction characterized by urinary incontinence or retention can also be present. During flexion and extension, patients often report electrical shock–like sensations up and down the spine, a myelopathy known as Lhermitte’s sign. This sign usually indicates severe spinal cord compression and a dynamic component, possibly with incompetent structural support.

Physical findings in myelopathic patients include lower motor neuron disease at the level of the lesion and upper motor neuron disease below the level of the lesion. Hoffman’s sign may be elicited by flicking the middle finger and observing flexion contractions of the thumb and index finger. Reflex abnormalities can include hyporeflexia at the level of the compromised nerve root and hyperreflexia distally. Other findings may include altered suspended sensory disturbances, diffuse spasticity, diffuse hand weakness, proximal lower extremity weakness, clonus, and Babinski’s sign. The differential diagnosis of patients with symptoms of cervical spondylosis who may have myelopathy can include intrinsic medullary tumors, syringomyelia, multiple sclerosis, extramedullary tumors in the cervical or thoracic spine, subacute combined degeneration, hereditary spastic paraplegia, amyotrophic lateral sclerosis, normal-pressure hydrocephalus, and arteriovenous malformations.^{2,20,29,41–43}

Axial neck pain can result from segmental instability caused by disk degeneration and from direct nerve root compression. Myofascial syndromes have also been implicated in the development of axial neck pain.⁴⁴ Occipital pain has been attributed to arthritic changes or instability at the C1 and C2 junction causing compression of the exiting C2 nerve root.⁴⁵ Shoulder pain may be related to cervical disk degeneration, brachial neuritis, or nerve root compression at C3, C4, or C5.^46–49

The symptoms of cervical radiculopathy follow a specific dermatomal pattern corresponding to the involved nerve root. These features can include loss of motor strength, decreased reflexes, loss of sensation, and well-delineated pain along the dermatome of the nerve root. The most common radiculopathies involve the C5, C6, and C7 nerve roots (also see Chapter 278).^24,50

In all cases of radiculopathy, the clinician can attempt to elicit radiating symptoms with provocative maneuvers. Spurling’s maneuver, performed by slight extension with lateral bending toward the symptomatic side and axial compression, can exacerbate and elicit radicular symptoms along a compromised nerve root.

Unusual manifestations of cervical spondylosis can include Brown-Séquard syndrome with ipsilateral hemiparesis, contralateral loss of pain and temperature sensation, and ipsilateral loss of joint perception.⁵¹ Although rare, an anterior spinal artery syndrome can result from thrombosis caused by compression of this vessel. This syndrome is associated with complete loss of motor function and sensation below the lesion with preserved joint and vibratory sensation. Vertebrobasilar insufficiency, manifested by nausea, vertigo, dizziness, and visual disturbances, has also resulted from osteophytic overgrowth in the transverse foramen.^52,53 Anterior osteophytic spurs can grow quite large and cause dysphagia. This condition, however, is rare because osteophytes grow slowly and the esophagus is flexible and mobile.^54,55

Diagnostic Studies

The diagnosis of cervical spondylotic myelopathy and radiculopathy includes the use of radiologic or electrophysiologic studies. Radiographic evaluation of cervical disease begins with comprehensive plain radiographic studies that include AP, lateral, and oblique views. Swimmer’s views are used to assess the cervicothoracic junction. Flexion and extension views can be helpful in patients with a history of trauma, evidence of spondylolisthesis, and previous surgical fusions. Plain radiographs must be evaluated carefully for the presence of congenital stenosis, misalignment, degenerative changes, and instability. A spinal canal less than 12 mm in diameter is considered to be abnormally narrow. One difficulty in relying on plain radiographs is the almost ubiquitous findings of cervical spondylosis in the aging population and the presence of degenerative changes in asymptomatic patients.^1,34,56,57 Moreover, plain radiographs are inadequate for the assessment of soft tissue compression, such as ligamentous and disk herniation.

Magnetic resonance imaging (MRI) has become the mainstay for assessing cervical degenerative changes. It is rapid and accurate and does not involve the use of ionizing radiation. It is now the preferred method for screening patients suspected of having radiculopathy or myelopathy (Fig. 280-1).^58–60 MRI clearly visualizes the neural elements, as well as ligamentous and soft tissue structures. High-intensity signals within the spinal cord occur in areas of severe compression and suggest intrinsic neural damage, which has implications for postoperative prognosis.^36,61–63 MRI can provide excellent visualization of ligamentous disruption caused by trauma.⁶⁴ This modality images the cervical spine in a multiplanar fashion, thereby facilitating visualization and anatomic definition of the disks and neural foramina and their compressive relationship to the exiting nerve roots. MRI can visualize bone marrow changes that suggest neoplastic, degenerative, inflammatory, or infectious processes. Moreover, MRI is a valuable tool for postoperative evaluation. However, it cannot adequately assess bony or osseous features, which should be imaged with computed tomography (CT).

FIGURE 280-1 A, A 65-year-old woman with a 2-month history of gait ataxia, hand numbness, and urinary incontinence was found to have multilevel cervical stenosis on T2-weighted sagittal magnetic resonance imaging. B, She underwent C4 corpectomy along with C5-6 and C6-7 diskectomy and allograft fusion and plating. Postoperatively, she had a short course of physical therapy and her symptoms resolved completely. Lateral radiographs at 6 months show incorporation of the allograft with no evidence of motion in flexion (C), neutral (D) and extension (E) views.

CT provides cross-sectional views of the cervical spine, which allows clear visualization of disk-osteophyte complexes and calcified ridges. Myelography via injection of a water-soluble contrast agent into the subarachnoid space can be used to visualize the spinal cord and segmental nerve roots. Lateral and AP radiographs provide limited definition of compressive lesions. However, the combination of cervical myelography with postmyelography CT provides excellent definition of osteophytic ridges, herniated disks, and their relationship to the nerve roots and spinal cord. In cases of severe compression, CT-myelography allows visualization distal to myelographic blocks.⁶⁵ CT-myelography is complementary to MRI for patients suffering from an ossified PLL and for those who have previously undergone instrumented fusion. In some cases, CT-myelography has provided enough definition to avoid vertebrectomy, thereby providing another point of fixation for the instrumentation and enhancing stability.

Electrodiagnostic studies can also be used to evaluate patients with radiculopathy or myelopathy. Such tests include electromyography (EMG), nerve conduction velocity (NCV), and somatosensory evoked potentials (SSEPs). These studies are usually performed when there are discrepancies between the clinical and radiographic findings or when other underlying conditions such as amyotrophic lateral sclerosis, multiple sclerosis, or peripheral neuropathy are suspected. EMG and NCV are performed concomitantly and can differentiate among radiculopathy, peripheral nerve pathology, and brachial plexus pathology. All of these electrodiagnostic tools suffer from a lack of specificity and sensitivity in localizing or grading the extent of compression. In selected cases, changes in SSEPs may serve as an objective measure of the progression of cervical spondylosis.⁶⁶ In their model of chronic spinal cord compression, Al-Mefty and coworkers³⁶ found that changes in SSEPs were present almost immediately before or at the time of initial neurological evaluation.

Preoperative diagnostic images must be evaluated carefully to ensure appropriate surgical planning.

Surgical Decision Making

Patients with radiographically proven spinal cord compression and myelopathic findings should be considered for surgery. Those with moderate to severe myelopathy should be offered surgery unless extenuating circumstances preclude surgery, such as significant medical comorbid conditions. Patients with significant cervical stenosis but no clinical symptoms could also be considered for prophylactic surgery to avoid a catastrophic neurological decline related to injury or progression of disease. This decision must be made with the patient after a full evaluation of the risks and benefits of the procedure.

Given the natural history of the disease, some surgeons believe that patients with only mild symptoms can be observed conservatively. As mentioned, the status of a significant proportion of patients will decline progressively. Most contemporary neurosurgeons do not consider cervical myelopathy to be a benign condition.

As with any surgical procedure, the risks and benefits to patients should be evaluated on a case-by-case basis. Factors such as age and medical comorbidity, which clearly influence the surgical outcome, must be considered. Boakye and colleagues pooled the data of more than 46,562 patients from the National Inpatient Sample who underwent anterior spinal fusion for cervical spondylotic myelopathy.⁶⁷ When compared with patients younger than 45 years, those 65 to 85 years old were 8 times more likely to suffer an adverse event after surgery. When compared with that same group, patients older than 85 years were 60 times more likely to experience an adverse event. Medical comorbid conditions such as hypertension, lung disease, diabetes, and obesity were also found to be predictors of adverse surgical events. Patients with one, two, and three comorbid conditions were 1.4, 2.2, and 2.8 times more likely, respectively, to suffer an adverse event when compared with patients without a significant comorbidity.

The decision to use an anterior approach instead of a posterior approach depends on multiple factors. Typically, however, the anterior approach should be used when most of the compressive pathology lies anterior to the spinal cord. The anterior approach should also be considered when a kyphotic deformity is present and lordosis needs to be restored. A simple diskectomy can be performed if the compression is at the level of the disk space, but corpectomy should be considered if the compression lies directly posterior to the vertebral body.

Operative Technique for the Anterior Approach

On the morning of surgery, informed consent is obtained, and unless contraindicated, for example, because of a history of trauma, the patient is asked to extend and flex the neck voluntarily to assess for any clinical symptoms. In this way the surgeon and anesthesiologist can limit their manipulations and not exceed the patient’s own range of motion. The anesthesiologist can also determine whether flexible fiberoptic intubation is necessary.

Once the patient is placed on the operating table, the anesthesiologist secures the airway via orotracheal access. When fiberoptic intubation is used, the patient is intubated awake under conscious sedation and local anesthesia. Once the patient is anesthetized, SSEP leads are placed so that functional feedback can be obtained during surgery. Appropriate venous access is obtained, and the patient is secured to the bed in a supine position.

Once the leads are placed, the patient’s neck is extended slightly. A small towel roll may be placed in the interscapular space, or the patient can be placed in a Caspar head holder (Fig. 280-2; Aesculap, San Francisco). Five- to 10-pound traction might be placed with the use of Gardner-Well tongs or an occipitomental traction device.

FIGURE 280-2 Patient positioning with the Caspar head holder. The patient’s head is maintained in a neutral position and secured by an elastic band around the chin that is attached to the frame. Cervical lordosis can be re-created by positioning the mobile neck holder in the midcervical or lower cervical region and by providing slight pressure on the posterior aspect of the neck. The shoulder can be taped to the frame or pulled down from the bottom of the table to improve visualization of the lower cervical region.

(With permission from Barrow Neurological Institute, Phoenix, AZ.)

The shoulders are taped to the foot of the bed or the hands are wrapped with a Kerlix bandage (Kerlix AMD, Covidien, Mansfield, MA). Securing the shoulders provides traction if the lower part of the spine needs to be visualized radiographically. The Kerlix bandage allows the hands to be pulled, which helps visualize the lower cervical spine. Care is exerted to avoid overstretching the shoulder to prevent a brachial plexus injury. Neurovascular structures at risk for compression are padded carefully. One dose of a prophylactic intravenous antibiotic is administered before the skin incision is made.

Surface landmarks do not correspond to exact levels of the cervical spine but do provide general reference points. The cricothyroid membrane identifies the C6 vertebral level. The thyroid cartilage corresponds to C3-4, and the space halfway between these two points corresponds to C4-5. The angle of the jaw corresponds to C2-3. For skin incisions, two fingerbreadths above the clavicle usually correspond to C6-7, and three fingerbreadths correspond to C4-5. The C6 anterior tubercle can be palpated in thin patients. C-arm fluoroscopy can also be used to determine where the skin incision should be made.

The side of approach depends on the surgeon’s preference. Right-handed surgeons prefer operating from the patient’s right. A disadvantage of operating from the right is a recurrent laryngeal nerve with an aberrant course. On the left side the thoracic duct may be in the surgical field in the lower spine. Patients with vocal cord paralysis must be approached from the side of the paralysis.

For simple one- or two-level diskectomies, a transverse incision is made along a skin crease. When multilevel diskectomies or corpectomies are being considered, the border of the sternocleidomastoid is incised obliquely (Fig. 280-3). The transverse incision should be 5 or 6 cm long and extend medially near the anatomic midline. Once the incision is delineated, the area is prepared and draped in sterile fashion. If an autograft will be harvested, this area, usually the left iliac crest, is also prepared for surgical access.

FIGURE 280-3 Lateral (A) and anterior (B) views of the patient’s position and planned skin incisions for single- or two-level diskectomies (dashed line) and multilevel diskectomies or corpectomies (dotted line).

(With permission from Barrow Neurological Institute, Phoenix, AZ.)

The platysma muscle is divided sharply either along its fibers or along the axis of the transverse incision. The platysma muscle is undermined by sharp dissection to permit adequate access to the deeper surgical field. Such undermining also minimizes the superficial tension that can rotate retractors. It is important to reapproximate this layer during closure for cosmesis.

Deep to the platysma muscle lies the anterior jugular plexus. The veins can be ligated or mobilized. Underneath the platysma muscle the medial border of the sternocleidomastoid is identified. The muscle may be mobilized with blunt dissection and retracted laterally. The laryngeal strap muscles are also identified and carefully mobilized medially. In an extended exposure of the lower cervical spine, the omohyoid muscle may be in the surgical field. This muscle can be divided if it will help in the exposure.

Once the sternocleidomastoid muscle is mobilized, the surgeon can feel the pulsations of the carotid artery with digital palpation. The carotid sheath is retracted laterally with Cloward retractors, and the trachea and esophagus are retracted medially (Fig. 280-4A). Two fascial layers, the pretracheal and prevertebral layers, are identified and easily dissected to expose the spine. The longus colli muscles are identified laterally, and the anterior longitudinal ligaments are seen to overlie the anterior aspect of the cervical spine. To identify the level of interest, lateral radiographs are obtained with a bayonetted spinal needle in the disk space or a Caspar distracting pin in an adjacent vertebral body (see Fig. 280-5A).

FIGURE 280-4 A, Axial view of the surgically relevant anatomic structures and plane of dissection. The carotid sheath and jugular vein are gently retracted laterally while the esophagus and trachea are mobilized medially. B, After lateral mobilization of the longus colli muscles, self-retaining retractors are placed underneath their medial border to obtain an ample and full view of the anterior cervical spine.

(With permission from Barrow Neurological Institute, Phoenix, AZ.)

FIGURE 280-5 A, A bayonetted spinal needle is placed at the desired level, and a radiograph is obtained to confirm the level. B, A Caspar pin retractor is placed in the middle of the vertebral body. C, An interbody spreader helps distract the collapsed disk space.

(With permission from Barrow Neurological Institute, Phoenix, AZ.)

Once the correct level is identified, the longus colli muscle is dissected laterally off the anterior vertebral body with bipolar cauterization and periosteal elevators. The muscle is mobilized from its medial insertion in a rostrocaudal direction to provide about 20 mm of exposure of the anterior aspect of the vertebral body, disk, or both. Aggressive dissection of the muscle can disrupt the sympathetic fibers that course along its medial edge or inadvertently injure the vertebral artery.^68,69

Once the muscle is mobilized, self-retaining retractors are placed with the teeth of the retractor underneath the muscle (Fig. 280-4B). Placing the retractors incorrectly can cause excessive retraction on the esophagus and carotid artery. A second set of retractors can be placed in a rostrocaudal direction to gain full exposure of the area of interest. Alternatively, Caspar distracting pins can be placed at the midlevel of the vertebral body to obtain adequate exposure and provide distraction to facilitate identification of the intervertebral space (see Fig. 280-5B and C).

Diskectomy and Corpectomy

Once the anterior aspect of the spine is exposed, the microscope is brought into the surgical field for the diskectomy. The diskectomy begins by removing the anterior aspect of the annulus fibrosis circumferentially with a sharp knife (Fig. 280-6). The superficial disk is resected with curets and pituitary rongeurs. When significant osteophytic ridges are present, a high-speed, small-diameter bur is used to approach the PLL cautiously. A mental picture of the midline is necessary to avoid wandering too far laterally. The Luschka joints are excellent anatomic landmarks that help the surgeon avoid inadvertent injury to the vertebral artery, which lies immediately lateral to the joint.

FIGURE 280-6 A, Once the area of interest is identified, the diskectomy begins with dissection of the annulus with a no. 11 blade. B, Next, the disk material is removed with curets or pituitary rongeurs. Distraction is applied and the posterior longitudinal ligament is resected with curets or thin-plated Kerrison rongeurs. C, The end plates are prepared by removing the cartilaginous surface with curets or a high-speed drill. A small posterior shelf is created to prevent retromigration of the graft into the spinal canal.

(With permission from Barrow Neurological Institute, Phoenix, AZ.)

Once the PLL is identified, we remove it to determine whether any subligamentous disk material is present. The safest way to elevate the PLL is by placing a blunt hook in the most lateral aspect of the canal near the exit of the nerve root where the PLL is weakest and thinnest. Sometimes, resection and drilling of the Luschka joint must be extended laterally. Once the PLL is elevated, it can be resected safely with upgoing curets or small Kerrison punches, which do not compromise the spinal canal during their insertion.

Central disk-osteophyte complexes can be removed safely by using thin-plated Kerrison punches and minimizing their protrusion into the spinal canal. Alternatively, osteophytes can be thinned, elevated, and removed with upgoing curets. In patients with radiculopathy, decompression of the foramen must be ample, which might require drilling and resecting the Luschka joints to visualize the exiting nerve root clearly (Fig. 280-7). Nerve root decompression can also be confirmed by palpating the pedicle of the lower cervical vertebrae with a blunt hook. Bleeding from epidural veins is controlled with low-powered bipolar coagulation devices or with other materials such as Surgifoam (Baxter, Deerfield, IL) or Avitene (MecChem, Woburn, MA).

FIGURE 280-7 A, Axial view of the final appearance of the operative site after diskectomy. The posterior longitudinal ligament has been removed to decompress the spinal canal. The foramen is also removed after osteophytectomy. B, Sagittal view of the operative site. The end plates are prepared with a high-speed drill to avoid retrograde and anterograde migration of the graft. C, The graft is placed under compression.

(With permission from Barrow Neurological Institute, Phoenix, AZ.)

When a corpectomy is performed, diskectomies are performed above and below the corpectomy sites to obtain a visual gauge of where the spinal canal lies (Fig. 280-8). The longus colli muscle is dissected laterally until the body begins to curve laterally and posterolaterally. The vertebrectomy can begin by using a narrow Leksell rongeur spanning from one disk to another. The rest of the corpectomy can be performed by using a high-speed drill and drilling deep into the posterior cortex. At this time the cortex is elevated with upgoing curets, and the PLL is identified posteriorly. Large emissary and epidural veins are carefully controlled with bipolar coagulation. At levels of severe compression, osteophytic ridges that might be adherent to the underlying dura are dissected carefully.

FIGURE 280-8 Sagittal views of the corpectomy site before allograft (A) or autograft (B) fusion. With an autograft there is no need to create posterior shelves because a screw can be placed into the autograft to prevent migration. C, Midlevel axial view through a corpectomy site after insertion of an autograft. The graft is oriented with the cortical margins anteriorly and posteriorly. This orientation serves to buttress the anterior and middle columns while minimizing the anteroposterior diameter of the graft to provide an added margin of safety between the graft and epidural space. C4 corpectomy is performed with allograft (D) or autograft (E) material and plating. The graft is not countersunk and the anterior margin of the graft contacts the plate. The allograft is packed with autologous bone particles obtained during the corpectomy to promote fusion.

(With permission from Barrow Neurological Institute, Phoenix, AZ.)

Once the central decompression is completed, thin-plated Kerrison punches are used to widen the canal from pedicle to pedicle. A decompression spanning 15 to 20 mm typically provides ample space. At the level of the vertebral body, extensive lateral dissection is unnecessary because myelopathy is a central phenomenon and radiculopathy, a more lateral phenomenon, is addressed during the diskectomy portion of the decompression.

Complications

Various complications have been reported after anterior spinal surgery, the most common of which are transient vocal cord paralysis, breathing difficulties, dysphagia, and odynophagia.^89,90 Permanent vocal cord paralysis is rare, and its incidence has been estimated to be 0.5% to 1%.^91,92 When hoarseness is present postoperatively, it usually resolves within weeks to months. Breathing difficulties may result from swelling of soft tissue after prolonged and excessive retraction or from postoperative hematomas. Large hematomas that compromise the airway should be addressed surgically. Several vital structures are also at risk for injury during anterior spinal approaches, including the carotid artery, jugular veins, trachea, and esophagus (Fig. 280-9).

FIGURE 280-9 Surgical anatomy relevant to anterior cervical approaches. ca, carotid artery; jv, jugular vein; rn, recurrent laryngeal nerve; sa, subclavian artery; sv, subclavian vein; t, trachea; tc, thyroid cartilage; td, thoracic duct.

(With permission from Barrow Neurological Institute, Phoenix, AZ.)

Careful dissection and meticulous attention to retractor placement should prevent injuries to these structures. The retractors need to be placed under direct vision beneath the longus colli muscle bilaterally to avoid inadvertent injury to the esophagus. Although rare, esophageal injuries carry significant morbidity with the possible development of mediastinitis and lethal abscesses. After surgery is completed, the length of the esophagus needs to be inspected thoroughly to check for rents. Methylene blue dye can be instilled into the pharynx while any suspicious areas are carefully visualized for extravasation of dye. If a rent is identified, it needs to be addressed and repaired primarily. Treatment of an infected esophageal repair requires surgical revision, drainage, nasogastric aspiration, intravenous or local antibiotics (or both), and in some cases esophageal diversion.^93,94

Severe neurological injuries are very rare after anterior cervical procedures.⁹⁵ Such injuries might result from surgical trauma, overdistraction with spinal cord impingement, or retropulsion of interbody grafts. If postoperative neurological deterioration is encountered, an epidural hematoma should be suspected and addressed in emergency fashion. Vertebral artery injuries are also rare and result from loss of midline orientation, screw placement, or aggressive resection of laterally placed disk osteophytes.⁹⁶ Cerebrospinal fluid fistulas are uncommon. They usually occur in patients with an ossified PLL and extensive dural adhesions. Most defects are small and can be handled by the local application of a Gelfoam pledget and fibrin glue and elevation of the head of the bed after surgery. In such cases, direct closure is technically difficult. If there are any concerns, lumbar drainage can be implemented with good results. Other rare complications can include Horner’s syndrome (anhydrosis, miosis, and ptosis) from interruption of the sympathetic chain located along the anterior surface of the longus colli, pneumothorax when addressing pathology located at the cervicothoracic junction, and thoracic duct disruption when the lower cervical region is approached through the left side.

Complications from iliac crest harvest can include localized pain, meralgia paresthetica from disruption of the lateral femoral cutaneous nerve, wound infections, and hip fractures. Use of an oscillating saw rather than an osteotome might reduce the incidence of hip fractures.⁹⁷ Graft displacement and angulation have been reported in 2% to 8% of cases.^70,98 A well-fitted graft under compression may reduce the incidence of this problem. Depending on the symptoms, these extruded grafts might require surgical intervention.

A risk for pseudarthrosis has been reported in most series addressing anterior cervical diskectomy and fusion.^{70,85,86,88,98–106} The rate of pseudarthrosis with a one-, two-, and three-level fusion has been reported to be as high as 20%, 50%, and 56%, respectively.^107–114 Recent studies of cervical plates have reported significant improvements in fusion rates for two- and three-level fusions.^87,115 The development of pseudarthrosis does not necessarily result in poor surgical outcomes. However, after patients with symptomatic pseudarthrosis undergo posterior fusion at the involved levels, their symptoms could resolve. Other potential complications with instrumentation include esophageal erosion and hardware failure. Use of a nonconstraining screw-plate interface might allow graft settling and prevent the plate and screw from breaking.

Conclusion

Treatment of cervical spondylosis requires careful and thorough evaluation by the clinician. Potential sources of pain and neurological deficits must be ruled out by appropriate diagnostic imaging, EMG, or both. Once the diagnosis has been narrowed to the cervical spine, an appropriate treatment plan should be devised. The degree and extent of neurological dysfunction determine the need for conservative or surgical management. Patients with radicular symptoms may be treated conservatively, whereas patients with myelopathic symptoms require careful and expeditious management. Most patients require surgery. The anterior cervical approach has enjoyed acceptance among spine surgeons and has evolved tremendously over the last 5 decades. This extremely versatile approach allows surgeons full access to most if not all anterior pathologic components responsible for clinical symptoms. Foraminal distraction, spinal cord decompression, and restoration of lordotic curvature can be performed by placement of a graft and subsequent stabilization if required. Fusion can be enhanced through meticulous end plate preparation, maximization of bone-to-graft contact, and compression. Excellent results are usually achieved with little or acceptable morbidity.