Introduction

Cervical spondylosis is a progressive degenerative process resulting in pathologic changes in the intervertebral discs and surrounding structures¹. Such changes include intervertebral disc protrusion, osteophyte formation, and hypertrophy of the lamina, ligaments, and hypophyseal joints.^2,3 Clinical onset can begin as early as the third decade, with progression continuing into the eighth decade.¹ Radiographic signs of spondylosis are evident in 50% of the population by the fifth decade, while prevalence is estimated at 98% for people over 70.⁴ Secondary myelopathy is considered to be the most common cause of spinal cord dysfunction in patients over 55.⁵

The effects of spondylosis can range from subclinical symptoms to primary root impingement (radiculopathy) and myelopathy. Proper diagnosis depends on meticulous history-taking, thorough physical examination, and the use of appropriate imaging, neurophysiologic, and laboratory tests. The natural history of cervical spondylosis is not well understood⁶, and treatment of spondylosis includes both conservative medical management and surgical intervention. A variety of surgical procedures have been well described including anterior and posterior approaches with or without fusion. This chapter reviews the relevant anatomy, pathophysiology, symptomatology, diagnosis, natural history, and management of cervical spondylosis.

Regional Anatomy of the Cervical Spine

Normal anatomy of the cervical spine consists of vertebrae, intervertebral discs, ligaments and joints, neural elements, and surrounding soft tissue and vascular structures.

Osseous Components

The bony cervical spine is composed of seven vertebrae (Figure 24-1A-C). The lower five segments (C3-C7) are similar in morphology, while the first two segments (C1 and C2) are anatomically distinct. The first cervical segment, the atlas (C1), is ring-shaped and articulates primarily with the occipital condyles above and the superior facets of the second cervical segment below. The second cervical segment, the axis (C2), has a cone-shaped projection (the odontoid process) that articulates with the anterior arch of C1. The remaining cervical vertebrae (C3-C7) share similar architecture; the vertebral bodies are roughly cylindrical in shape and increase in size from rostral to caudal. From each body projects an uncinate process superiorly, which indents the posterolateral margins of its respective intervertebral disc. The transverse processes project anterolaterally and house the foramen through which the vertebral arteries pass. The spinal cord runs through the spinal canal, which is formed by the posterior elements including the pedicles, the facet joints, the lamina, and the spinous process. At each level, nerve roots exit the canal between vertically adjacent pedicles (Figure 24-1C,D)

FIGURE 24-1 A, A lateral view of the cervical spine demonstrates the relationship of the cervical facets with the angled superior and inferior articulating facets and their encasing articular capsules. The anterior intervertebral discs and bodies are also seen. The spinous processes and dorsal arches are significantly stabilized by the dorsal interspinous and supraspinous ligaments. B, A posterior view of the cervical spine demonstrates the complex arrangement of the dorsal stabilizing musculoligamentous complex and its attendant musculature. C, An anterior view of the cervical spine demonstrates the anterior longitudinal ligament connecting the vertebral bodies at the level of the discs as well as the intertransverse ligaments between the transverse processes. The relationship of the vertebral arteries coursing rostrocaudally through the foramina transversaria is also shown. D, An axial view of a cervical segment shows the spinal canal containing the neural elements which are stabilized and held in place within the subdural space by the dentate ligaments. The nerve roots with their dorsal root, ventral roots, and spinal ganglia are shown as well. The dorsal arch of the ligamentum flavum lies directly below the neural elements. Again shown are the vertebral arteries within the foramina transversaria with their relationship to the nerve root and the uncinate joint.

The unique morphology of C1 and C2, as well as the increasing vertebral body size of the lower segments, may contribute to the pathogenesis of spondylosis. The anteroposterior diameter of the canal is generally larger at C1 and C2 when compared to the lower vertebrae; thus the spinal cord is estimated to occupy only one third of the atlantal ring at C1, while it occupies up to three fourths of the canal in the lower segments. This variability may account for the predisposition for spinal stenosis with symptomatology at the C4-C7 levels.⁷

Pathophysiology of Cervical Spondylosis

Cervical spondylosis is a multifaceted degenerative process that can affect all components of the spine including the intervertebral discs, facet joints, ligaments, spinal soft tissues, and bony elements. The initial pathological changes in spondylosis originate in the disc space. The proposed mechanism of disc degeneration occurs secondary to an alteration in the protein composition of the disc matrix. With aging, the molecular weight of the glycoproteins in the disc decreases along with the chondroitin sulfate content. The net effect is a change in the osmotic properties of the disc, with decreased inflow of fluid. Dehydration of the disc leads to loss of height, as well as loss of expansion capability under axial loading. As the disc progressively loses the ability to distribute normal loads of pressure, the nucleus pulposus becomes predisposed to fragmentation. Fragmentation of the nucleus combined with increasing weakness in the annulus with aging can result in herniation of disc material into the spinal canal (Figure 24-2A).

FIGURE 24-2 A, A posterolateral disc herniation is shown in this spondylytic cervical spine segment, causing compression of the nerve root at the level of the foramen without compromise of the cord itself. When symptomatic, such lesions are typically associated primarily with radicular complaints. B, Multilevel spondylytic osteophytes combined with chronic disc herniations contribute to a severely narrowed central canal that can be associated with central hemorrhage and myelomalacia. Clinical syndromes include central cord syndrome and cervical myelopathy. C, A T2-weighted axial MR image of a cervical posterolateral disc herniation provides an example of root compression in cervical spondylosis. The cord, although displaced, is not significantly compressed. D, A T2-weighted sagittal MR image demonstrates multilevel spondylytic changes with disc herniations, ultimately causing significant canal stenosis and spinal cord compression. T2-signal changes within the parenchyma of the spinal cord demonstrate injury to the substance of the neural elements.

Loss of disc height not only contributes to disc herniation, but also results in osteophyte formation. As the annulus bulges under the impaired function of the damaged disc, the periosteum of the adjacent vertebral bodies undergoes reactive processes. Hyperostosis of the subperiosteal bone generates a spondylotic ridge or osteophyte, which can impinge on the ventral canal to cause cord compression. Spondylosis also leads to hyperostosis of the posterior elements. In the dorsolateral spinal column, decreased disc height causes pathological changes in the facets with destruction of the joints and resultant hypertrophy. Abnormal mobility of the spine contributes to osteophyte formation in the neural foramina, leading to peripheral nerve compression and radiculopathy. As spondylosis progresses, the ligamentum flavum becomes hypertrophic and loses elasticity. During hyperextension especially, the ligament tends to buckle inward, contributing additionally to canal compromise.¹⁰

The mechanism by which spondylosis leads to cord injury is not entirely understood; the pathophysiology is complicated by the common absence of symptoms in patients with radiographic evidence of significant disease.¹¹ Spondylosis with disc herniation, osteophyte formation, and ligament hypertrophy clearly reduces the anterior-posterior diameter of the spinal canal. As expected, patients with congenitally narrow canals are therefore more prone to be symptomatic. Studies have suggested that the normal canal diameter is 17 to 18 mm (C3 -C7) and that a reduction in axial diameter to 11 to 13 mm is more likely to lead to myelopathy.¹⁰ Abnormal cervical motion and instability following degenerative changes may exacerbate cord injury. With neck flexion, the cord may move against the ventral spondylotic ridges causing cord damage. Extension may lead to cord strangulation between the folded ligamentum flavum posteriorly and osteophytes or herniated disc material anteriorly (Figure 24-2B).

There is considerable debate as to whether cord injury is due to direct compression of neural structures or secondary to extrinsic compromise of vascular supply. The vascular ischemia theory was first proposed in 1954 by Brain.² Breig noted later that in cervical flexion, mechanical flattening of the spinal cord occurred, with consequent decreased patency of the anterior sulcal and transverse arteries.¹² Other authors have noted that anterior-posterior compression of the spinal cord in both pathologic and experimental studies resulted in stretching of the transverse vessels and terminations of the anterior spinal artery with ischemia of the anterior two thirds of the cord.^8,13,14,15 Clinically, Allen noted that the cervical spinal cord blanched during flexion in patients with spondylosis.¹⁶

Human pathologic studies of cervical spondylosis demonstrate that canal compromise with cord compression results in characteristic histological changes. Ono et al. found that compression of the cord is associated with extensive destruction of both gray and white matter, with consequent demyelinization.¹⁷ Interestingly, the areas of the cord most encroached upon tend to display histopathological evidence of severe infarction. Ogino et al. demonstrated an association between localized infarction of the gray matter and a decrease in the anterior-posterior canal ratio to below 20%.¹⁸ As cord injury secondary to spondylosis progresses, tissue destruction leads to gliosis, scarring, cystic degeneration, and neuronal cell loss.

In conclusion, the pathophysiology of spondylosis appears to be the result of several degenerative processes that occur in conjunction. The decrease in disc height leads to herniation, reactive hyperostosis with osteophyte formation, and hypertrophy of the ligaments. These events, along with abnormal cervical motion, compromise the cord within the canal. The mechanism of cord injury is still not well understood but appears to be related to impaired vascular supply leading to neuronal ischemia. As spondylosis becomes more severe, pathological changes of the cord become evident: demyelination, gliosis, cystic degeneration, and neuronal cell loss.

Clinical Presentation of Cervical Spondylosis

Cervical spondylosis can present with a variety of clinical syndromes. Pain may be localized to the neck or display a radicular pattern. Weakness can occur as a mixture of upper and lower motor neuron findings. Lower motor signs generally predominate at the level of the lesion, while upper motor findings are present at segments below. Atrophy and diminished reflexes are common in the involved upper extremity. Lower segmental involvement presents as hyperactive reflexes, increased tone, clonus, or (most commonly) abnormal gait. Sensory impairment is highly variable, with patchy sensory loss in both the upper and lower extremities occurring along three neural pathways. Pain and temperature sense are often affected contralateral to the lesion, due to spinothalamic tract fibers crossing at levels near their entrance into the canal. The posterior columns, which convey position and vibration sense, decussate in the brain stem and therefore are often affected ipsilateral to the lesion. Spondylosis can also affect the dorsal root as it enters the canal, resulting in impaired dermatomal sensation.

Myelopathy is a common and severe manifestation of cervical spondylosis.⁵ Symptoms may be slowly progressive and associated with intermittent periods of remission and exacerbation.²⁰ Clinical presentation generally consists of lower motor neuron involvement at the level of the lesion, with upper motor neuron signs at segments below. Upper extremity involvement is often unilateral, while that of the lower extremity is bilateral. Lower motor neuron findings include weakness and atrophy with progressive loss of dexterity, particularly at the level of the lesion. The lower extremities may demonstrate spasticity, clonus, hyperreflexia, or abnormal gait, with a positive Babinski sign. Sensory disturbances are poorly localized, generally affecting the lower extremities and trunk, while rarely involving cervical levels.²⁰ Bowel and bladder impairment are rare, but indicate poor prognosis.

Due to the complex symptomatology of cervical degenerative disease, Crandall et al. described five clinical syndromes to aid in clustering various findings.²¹

Among other possible findings is the “numb, clumsy hand.”²³ This condition involves a glove-like distribution of primary sensory loss combined with motor loss. Tandem spinal stenosis simultaneously affects the cervical and lumbar regions, presenting with a trio of symptoms: neurogenic claudication, gait abnormality, and mixed upper and lower motor neuron signs.²⁴ Vertebral artery insufficiency can present with dizziness and unsteadiness when the head is rotated.²⁵ Rarely, large osteophytes can cause dysphagia due to direct compression of the esophagus.⁵

It is important to consider other neurological conditions that may exhibit symptoms mimicking cervical spondylosis. Any mass lesion within the spinal canal that compresses the cord or nerve roots can manifest with such findings. Extradural, intradural, and osseous tumors of the spine, as well as infectious processes such as epidural abscesses, can compromise canal integrity. Fortunately, these conditions can generally be distinguished from cervical spondylosis via effective MRI. Multiple sclerosis is another condition commonly confused with cervical spondylosis, and a mixed picture of upper and lower motor neuron signs is a hallmark finding in amyotrophic lateral sclerosis. Correctly diagnosing cervical spondylosis depends on detailed history-taking, complete neurological examination, and diagnostic measures including imaging, neurophysiology, and laboratory tests.

Diagnostic Modalities

Natural History of Cervical Radiculopathy

The natural history of cervical spondylosis is not well described. Since early descriptions of the condition, surgery was widely accepted as the treatment of choice, and no studies were made to determine long-term progression. Only a few investigators have attempted to formulate a likely picture using patients treated with a collar.

Lees and Aldren-Turner classified cervical spondylosis as a relatively benign condition.¹⁹ The common course experienced by their patients was characterized by long periods of stable symptomatology interspersed with short bouts of deterioration; chronic, gradual deterioration was rare. They also found that myelopathy did not develop in a group of patients presenting solely with radiculopathy. In following studies, Nurick agreed with the findings of Lees and Aldren-Turner, and also found that patients who had undergone surgical laminectomy had no significant improvement over those with no treatment.³ Thirdly, he realized that age of onset served to significantly determine the prognosis for later deterioration.

When comparing 48 patients who underwent surgery with those in Lees and Aldren-Turner’s study, the other authors found that 70% of patients enjoyed improved conditions from cervical laminectomy. Their conclusion was that patients with moderate or severe symptoms due to cervical spondylosis benefit greatly from surgery, whereas those with mild disability are not likely to be significantly helped. Doubt was later cast upon Lees and Aldren-Turner’s theories in that they were thought to have bias toward milder cases.

Scoville found that the best outcome of surgery was in patients treated within one year of onset of symptoms.⁴⁸ He further elaborated on Lees and Aldren-Turner’s model in claiming that patients should be treated surgically, shortly after mild disability was noticed, and before further progression. He did admit that mild cases were adequately treated conservatively.

Smith and Robinson more recently described the course of cervical spondylosis that is most accepted today.⁴⁷ They found that motor complaints tended to be more permanent than neck, bladder, and sensory symptoms. Motor findings were also predominant in the lower extremities, and sensory in the upper. Although most of their patients followed an episodic but unpredictable pathway, one third of cases were found to be nonprogressive between acute episodes, while two thirds experienced a gradual increase in symptoms between intermittent, acute episodes of worsening. A minority of patients had a constant worsening in condition, and very few people enjoyed spontaneous improvement. Their conclusion was that although progression of the disease is usually slow, prognosis is poor, and improvement rare. They hypothesized that patients reporting improvement may simply be coping better, or may simply be reporting a slowing of progression.

Although many agree that there is a need to compare the outcome of different surgical treatments for cervical spondylosis with the natural history, such a study would be unethical. As surgery is widely accepted as incontrovertibly beneficial, it would prove difficult to randomize patients with severe or progressive disability to nontreatment.

Treatment and Decision-Making

Two options exist for treating cervical spondylosis: conservative and surgical. Conservative treatment is aimed toward patients with milder symptoms and can range from simply monitoring the patient to isolating the neck with a hard or soft collar. The collar should hold the neck either neutral or slightly flexed, with duration of use varying between patients. Drug therapy is another option in nonsurgical treatment, consisting of analgesics, muscle relaxants, and nonsteroidal antiinflammatory drugs. Analgesics are used to relieve acute pain episodes, and muscle relaxants to reduce muscle spasm (which can lead to pain and ischemia) and increase range of motion. The goal of antiinflammatory therapy is to reduce impingement upon nerve roots due to inflammation. It should be noted that drug therapy is recommended as a supplement to immobilization; rest is the best conservative way to reduce symptoms.

Surgical intervention is used when patients suffer moderate, severe, or progressive disability. A definite diagnosis must be made before surgery is used to reduce narrowing of the canal and stabilize the vertebral column.

Posterior Cervical Surgical Techniques

Cervical laminoforaminotomy and laminectomy is the classic posterior approach used in treating cervical spondylosis, and is still used in patients suffering posterior canal compression from a hypertrophic ligamentum flavum. In this procedure, the lamina is removed from the affected level and those adjacent to it; foraminotomies may also be performed to relieve radiculopathy. This surgery is contraindicated in patients lacking normal cervical curvature or suffering from cervical instability. In the latter case, laminectomy may be performed if preceded by anterior cervical fusion.

Laminoforaminotomy and laminectomy should be performed under general anesthesia, with the neck in a neutral position to prevent stretching of the spinal cord over any anterior protrusions within the canal. The patient can either sit or lie prone; the former allows a dry field, but increases the risk of an air embolism. After proper fixation of the head in pins and/or traction as noted above, radiographic assessment of the spinal alignment and confirmation of the neurological exam should be obtained prior to incision (Figure 24-3A). A midline incision is then made over the pathology in question. For occipitocervical fusions, this incision should typically extend from the inion on the skull to slightly above the C7 prominence. A more limited incision can be made for subaxial cases. Due to the narrowed interspaces and inferior inclination of the spinous processes, overdissection and stripping of the facets may lead to unwarranted fusion of uninvolved levels, leading to an excessive decrease in mobility.

FIGURE 24-3 A, For posterior approaches, the patient is typically positioned prone, either on a horseshoe or in surgical Mayfield pins as shown here. The arms are typically tucked downward to maximize surgical exposure. B-C, Dorsal midline exposure of the posterior cervical musculature with section of the interspinous ligaments reveals the underlying dorsal bony arches with the lamina and spinous processes. Wider dissection exposes the pillars of the articular facets with their bodies and the articular capsules encasing the joint spaces themselves.

The dissection is carried down sharply in the midline to the level of the posterior cervical musculature fascia. A midline raphe is formed from the union of the deep cervical fascia, prevertebral fascia, ligamentum nuchae, and the supraspinous ligaments (Figure 24-3B). By maintaining the exposure in this relatively avascular midline plane, blood loss can be minimized. Frequent palpation of the bony processes demarcating the midline is essential. Self-retaining retractors are placed to maintain the exposure, but excessive retraction can obscure the midline and lead to scything to either side.

After the ligamentum nuchae is encountered over the cervical spinous processes, a subperiosteal dissection is performed to mobilize the muscles off the processes. As the processes are often bifid, care should be taken to avoid accidental spinal canal entry. The exposure is then carried down to the lamina which are palpated and identified. Using gentle lateral retraction with a small Cobb elevator, electrocautery is used to dissect the muscles off the lamina (Figure 24-3C). Excessive downward pressure with the elevator must be avoided, as the cervical spine is highly mobile even in its normal state under anesthesia. The laminae of the cervical spine are angulated 45 degrees from medial to lateral and also in a cephalic direction. The interlaminar areas are also wide and should be exposed cautiously. It is here that the venous plexus overlying the vertebral artery is often encountered as the facet capsule is exposed. Bipolar cautery and gentle tamponade with Gelfoam are usually effective in obtaining hemostasis. For uninvolved levels, care should be taken to preserve the facet capsule (zygapophyseal joint). Self-retaining retractors to maintain exposure should be placed at or above the anteroposterior plane of the facets to avoid injury to the nerve roots and vertebral artery.

Alternatively, a minimally invasive paramedian tubular approach can be used as well. A stab incision is initially made approximately 1 cm off midline ipsilateral to and at the level of the pathology. Under fluoroscopic guidance, a small tubular dilator or pin is inserted through the posterior cervical musculature and fascia down to the facet or lateral mass of the target level. Although we have not routinely done so, anteroposterior radiographic images could be obtained to guarantee proper pin positioning (Figure 24-4A). Once the dilator has been docked on the facet in question, the skin incision is extended above and below the Steinmann pin for a total length of approximately 2.0 cm. The skin edges are retracted and the cervical fascia is incised using Metzenbaum scissors. Care should be taken not to cut muscle fibers during this procedure, as this can cause unnecessary blood loss. This sharp opening of the fascia allows for easier passage of the sequential dilating cannulas with a minimum of force (Figure 24-4B). A series of dilators is then sequentially inserted through the neck soft tissues, over which an 18mm tubular retractor is then inserted (Figure 24-4C). Real-time lateral radiographic images are obtained as often as needed to insure a proper working trajectory throughout this process (Figure 24-4A-C). The working channel (tubular retractor) is then attached to a flexible retractor affixed to the operating table side rail, and locked in position at the junction of the lamina and lateral mass (Figure 24-4D).

FIGURE 24-4 A-D, Lateral intraoperative fluoroscopic images demonstrate sequential tubular dilation of the dorsal musculoligamentous complex with ultimate docking of a working portal at the level of the C5/6 posterior laminofacet junction and disc level.

Once the standard or minimally invasive retractor is set in the desired position over the correct level as confirmed by fluoroscopic imaging, a Bovie cautery with a long tip is then used to remove the remaining muscle and soft tissue overlying the lateral mass and facet. Typically loupe magnification or an operating microscope is used for maximal visualization. With the bone well delineated, a small straight cervical curette is used to scrape the inferior edge of the superior lamina and the medial edge of the lateral mass/facet. This exposure is then carried underneath the lamina and facet with the use of a small angled curette. Proper placement of the curettes can be confirmed under fluoroscopy. Good dissection of the underlying flavum and dura from the bone defines the relevant anatomy and helps to prevent incidental dural tears. Bleeding from epidural veins and the edge of the flavum is controlled via long-tipped bipolar cautery. A small angled Kerrison rongeur is then utilized to begin the foraminotomy. Periosteal and bone bleeding is addressed with bone wax and cautery. In cases of marked facet arthropathy and enlargement, a drill with a matchstick-type bit is used to further thin the medial facet and lateral mass (Figure 24-5A,B). Dissection with an angled curette facilitates safe use of the Kerrison rongeur. In this fashion, the decompression is continued.

FIGURE 24-5 A–D, After exposure and confirmation under fluoroscopy, a high-speed drill burr is used to decompress the laminofacet junction. The lateral aspect of the cord and the exiting nerve root are exposed (A). Immediately investing these structures is the epidural venous complex, which often requires hemostasis via tamponade and bipolar cautery (B). The decompression is confirmed with the use of a nerve hook or probe to palpate the course of the exiting nerve root (C). For cases where fragmentectomy is required, a small retractor is used to elevate the nerve root to gain access to the disc space (D).

The laminoforaminotomy is completed when the nerve root has been well exposed along its proximal foraminal course. The adequacy of the decompression should be confirmed by palpating the root along its course with a small nerve hook (Figure 24-5C). In cases in which a herniated disc was present, either a nerve hook or small #4 Penfield elevator is used to mobilize the nerve root superiorly to expose the disc space and fragment. For this maneuver, additional exposure is obtained by drilling a small portion of the superomedial portion of the pedicle directly below the exiting nerve root. With the root retracted, the disc fragment is then removed in a standard fashion with curettes and long endoscopic pituitary rongeurs (Figure 24-5D). Additional osteophytes encountered in this region can also be drilled or curetted as needed. Upon completion of the discectomy and decompression, the nerve hook is again passed along the exiting root to confirm its free passage and a lateral fluoroscopic image is obtained.

After inspection of the nerve root, hemostasis is obtained by bipolar cautery and gentle tamponade with thrombin-soaked Gelfoam pledgets. The area is then copiously irrigated with lactated Ringer’s solution impregnated with bacitracin. A small piece of Gelfoam soaked with Solu-Medrol is gently placed over the laminoforaminotomy defect. A soft collar can be fitted for patient comfort, but is not necessary, as early mobilization is recommended. Major complications consist of wound healing and infection.

Anterior Cervical Surgical Techniques

Another surgical option is the anterior approach, which allows for fusion of the vertebral column concurrent with removal of osteophytes and prolapsed discs protruding into the anterior space of the canal. This approach is preferred in cases involving compression at one or two levels (although it is rarely performed in cases with three or four), and is particularly useful for patients with cervical instability. Several variations upon this method have arisen since its inception, with none having a distinct advantage.

As with laminectomy, this procedure is performed under general anesthesia, with the neck in a neutral position. The patient is placed in supine position with a roll placed transversely between the scapulae in order to extend the neck (Figure 24-6A). Following palpation of landmarks, a 2 to 3 cm skin incision is made along a skin crease at the level of interest between the sternocleidomastoid (SCM) and slightly off the midline (M) (Figure 24-6B). Finally, ensuring the correct level of the skin incision also prevents difficulty in dissection. Palpable landmarks in the neck aid in identifying the approximate level. The inferior angle of the mandible corresponds to C2-3; the hyoid bone to C3; thyroid cartilage to C4-5; the cricoid cartilage to C6, and the carotid tubercle to C7. Alternatively, a longer oblique or longitudinal incision can be made if an extensive decompression is planned (i.e., greater than 3-level corpectomy). Injection of lidocaine with epinephrine into the skin prior to incising may help diminish superficial bleeding.

FIGURE 24-6 A–C, For anterior cervical approaches, the patient is positioned supine, often with either a chin strap or traction tongs to optimize the exposure and the cervical lordosis. The C-arm can be draped in as well (A). The incision is marked at the level of the pathology, based on either anatomic landmarks or fluoroscopic guidance between the sternocleidomastoid [SCM] and the midline [M] (B). The surgical course is a lateral-to-medial type of trajectory passing through the skin, platysma, and the external cervical fascia (C). Once opened, this potential viscerocarotid space is split between the carotid sheath [C] laterally and the trachea [T] and esophagus [E] medially. The retractors are ultimately secured at the level of the prevertebral space at the anterior border of the spine (A).

Incise the superficial fascia overlying the platysma along the skin incision. The subsequent surgical course is through a potential space through the trajectory demonstrated in Figure 24-6C. The fibers of the platysma muscle are then either incised longitudinally along the direction of its fibers or split transversely. The deep cervical fascia underneath is then identified. Next, palpate the medial border of the sternocleidomastoid muscle and carefully split the fascia longitudinally. This allows one to retract the SCM laterally. The laryngeal strap muscles (sternohyoid, sternothyroid) as well as the midline structures immediately deep to them (trachea [T] and esophagus [E]) are then retracted medially. Deep to the SCM muscle, identify the carotid sheath (C) as well as the pretracheal fascia overlying it. Carefully incise the fascia medial to the sheath while protecting the midline structures. The carotid sheath can now also be retracted laterally.

Using blunt dissection, develop a plane toward the midline until the prevertebral fascia directly anterior to the vertebral bodies can be visualized. Identify the midline of the vertebral bodies (corresponding to the white stripe of the anterior longitudinal ligament) as well as the longus colli on each side. Using electrocautery, incise the prevertebral fascia longitudinally to the desired length. Use a periosteal elevator to then subperiosteally uncover the vertebral bodies and intervening disc spaces (A). Place retractors under each longus colli muscle to protect surrounding structures. The view of the field is provided by an operative microscope, which minimizes risk of injury during cord decompression. Place a spinal needle in a disc space and obtain a cross-table lateral film of the cervical spine to confirm the level. An assistant pulling axially on wrist straps depresses the shoulders and allows for a better radiograph. After confirming the level, a discectomy and/or corpectomy can be performed as indicated. Distraction pins can be placed in the appropriate vertebral bodies, and general distraction applied to facilitate discectomy and decompression, particularly in heavily collapsed spaces (Figure 24-7A).

FIGURE 24-7 A–B, After developing flaps under the longus colli laterally, the retractor blades are then secured underneath them to provide exposure to the spine. If desired, Caspar-type distraction pins can be secured into the surrounding vertebral bodies (A). Annulotomies are then made with a scalpel blade and discectomy completed with a combination of angled curettes, drill, and Kerrison and pituitary rongeurs (B).

The prolapsed disc and osteophytes are removed, and a bone graft is inserted within the interspace to provide stability and promote fusion. Typically, straight and angled curettes are used to free the disc and cartilaginous portions of the endplate from the bony vertebral body surfaces. Fragments of disc are then removed with pituitary rongeurs (Figure 24-7B). This process is gradually advanced down toward the level of the posterior longitudinal ligament (PLL). At times, drilling with a matchstick-type high-speed drill bit is useful to flatten irregular endplate osteophytes as well as to remove anterior closing lip osteophytes. Particular attention, however, should be taken to avoid excessive damage to the bony endplates, especially if grafting will be done, to prevent excessive subsidence of the graft. The PLL is then opened sharply with a small 1- or 2- mm Kerrison rongeur. Initial opening can be facilitated with the use of a small nerve hook probe. The PLL is then sectioned to reveal the underlying dura as needed, depending on the exact extent and location of the neurological compression as determined by the preoperative imaging and the patient’s clinical symptoms. It is particularly important to extend the decompression rostrocaudally by undercutting the marginal endplate osteophytes in an hourglass shape to ensure that there is no residual canal or foraminal compression (Figure 24-8A). The majority of surgeons, therefore, choose to remove larger osteophytes from posterior and posterolateral canal surfaces. Some surgeons also choose to open and excise the posterior longitudinal ligament. Doing so allows prolapsed discs to be more easily identified for removal (which is useful in up to 35% of cases). Further, excision of the ligament provides prophylaxis against buckling, a possible source of postoperative pain.

FIGURE 24-8 A–C, Typically a funnel or hourglass-shaped decompression is carried through the disc space to avoid inadvertent injury to the vertebral arteries, which are lateral at the level of the midbody (A). Widening of the exposure at the level of the canal and foramen is essential to ensure adequate decompression of the neural elements. Once the discectomy is completed, most surgeons opt to place an interbody graft comprised of either autograft bone, allograft bone, or synthetic material (B). A variety of specific interbody grafting techniques including the Smith-Robinson impacted type, the Cloward dowel, and the Bailey-Badgely slot type grafts have been commonly employed over the years (C).

Autologous bone grafts are usually taken from the iliac crest (over 70% of the time), with other options including the patient’s tibia or fibula, bone banks, and calf bone (Figure 24-8B). Artificial grafts are also possible using methylmethacrylate, hydroxyapatite, or biopolymer. Although such materials do not necessarily provide a better outcome, donor site pain can be eliminated. Benefits of fusion include reduced risk of repeated spinal cord injury and pain by minimizing abnormal movement, as well as prevention and treatment of residual or recurrent nerve root compression via loss of disc space height. Another advantage of fusion is increased resorption of osteophytes, although complete resorption may take several years. A variety of specific interbody grafting techniques including the Smith-Robinson impacted type, the Cloward dowel, and the Bailey-Badgely slot type grafts have been commonly employed over the years (Figure 24-8C).

The necessity of grafts is questioned, however, in that fusion occurs in over 75% of patients who do not receive a graft. The first reported anterior cervical decompression surgery without fusion was in 1960. In this procedure, the disc is resected to achieve decompression, and the space is left empty. The nonfusion anterior approach is used in patients suffering acute soft disc prolapse with minimal osteophyte formation, and neurological outcome is outstanding. Patients tend to have shorter recovery time with fewer complications. When osteophytes must be removed, the outcome is generally not as good as with fusion; many patients suffer new or recurrent pain symptoms. As such, the majority of modern surgeries now employ grafting with or without plating.

Vertebrectomy with strut grafting is a more recent surgical tool used in treating patients suffering from severe disease at many levels. Significant improvement is reported in 70% to 80% of cases, and many authors feel that this procedure is superior to other surgical options. When performing vertebrectomy, a trench is drilled out along the axes of the affected vertebra and disc spaces to achieve decompression, and the column is reconstructed using a graft from the iliac crest, rib, or fibula. In cases requiring immediate stabilization, titanium or PEEK implants can be used to reinforce the vertebral column, while also providing magnetic resonance imaging compatibility for postoperative imaging.

Anterior cervical microforaminotomy is a well-established minimally-invasive anterior cervical procedure and has the advantage of good decompression of the nerve root and maintenance of spinal stability without the need for fusion.^. Technically more demanding, decompression of the nerve root is achieved by removing the osteophytes from a lateral to medial trajectory with a focus on preserving the structural stability of the remaining joint and intervertebral disc (Figure 24-9A,B). Small slim retractors are docked at the junction of the lateral uncinate joint and the transverse process, immediately medial to the vertebral artery at the level of the disc and exiting nerve root (Figure 24-9C). With the vertebral artery retracted laterally, curettes and drill bits are used to expand the foramen and decompress the lateral aspect of the uncinate joint through the dorsolateral osteophyte (Figure 24-9D). Once exposed, the disc herniation is resected with micropituitary forceps (Figure 24-9E) to thereby ultimately decompress the neural foramen and exiting root (Figure 24-9F).

FIGURE 24-9 A–F, Anterior cervical microforaminotomy is a slightly more lateral approach than used in standard anterior midline cervical disectomy, and instead focuses on the lateral aspect of the disc space at the level of the neural foramen immediately medial to the vertebral artery (A, B). Once exposure is obtained with slim-blade type retractors between the uncinate joint and the vertebral artery laterally (C), curettes and drills are used to complete the bony decompression and foraminotomy (D). The herniated fragment is exposed and resected with micropituitary forceps (E) to ultimately complete a good decompression of the neural elements (F).

Surgical Outcomes

Assessing the results of surgery for cervical spondylosis has proved difficult for many reasons. As the disease is heterogeneous in presentation, studies include a variety of cases disparate in age, extent of vertebral involvement, and severity of symptoms. To date, no prospective, randomized experiments have been published. Currently available publications consist mostly of retrospective reviews of different procedures performed at the same institution. Furthermore, there is no standardized method of assessment. The Japanese Orthopedic Association proposed a scale involving four-limb function and bladder symptoms. The Odum scale grades from excellent to poor, and the Nurick system assesses ability to walk. Magnetic resonance has been used to determine the underlying cause of poor postoperative results. In examining 56 patients, Clifton found that only 12 patients had adequate decompression at the correct levels, whereas 32 cases had either residual compression at operated levels or untreated compression at additional levels.⁵⁵ Batzdorf and Flannigan similarly found patients with residual cord compression.⁵⁶Harada found that when significant decompression was not achieved, recovery was significantly worse.⁵⁷ In light of these findings, the necessity of preoperative imaging for accurate determination of involved levels and best method of approach becomes apparent.

The effectiveness of posterior cervical laminoforaminotomy for decompression of the lateral recess and neural foramen has been well documented in numerous publications over the last four decades.^48,49 When compared to standard anterior cervical techniques, the posterior approach via a “keyhole” type of osteotomy may provide better exposure for decompression of the exiting root and for removal of lateral osteophytes and discs. Previous work examining laminoforaminotomy has shown that adequate foraminal exposure can be accomplished without necessarily destroying the facet joint or causing iatrogenic instability.⁵⁰ As long as less than 50% of the facets are removed, there is little compromise of the sheer biomechanical strength of the cervical spine.⁵¹ The posterior approach also avoids the additional risks of injury to the anterior structures of the neck including the trachea, esophagus, thyroid, thymus, carotid arteries, jugular veins, vagus nerve, recurrent laryngeal nerve, superior laryngeal nerve, ansa cervicalis, and thoracic duct. Lastly, cervical laminoforaminotomy is an operation that treats the offending pathology without necessitating a fusion. As longitudinal studies now demonstrate an increased incidence of adjacent level problems following cervical fusion, avoiding arthrodesis when possible seems particularly prudent.⁵² Overall, no statistically-significant difference in results between anterior and posterior approaches for the management of isolated cervical radiculopathy has been demonstrated.⁵³ The overall clinical popularity of laminoforaminotomy was tempered by technical limitations including a limited surgical view, difficulty in resecting osteophytes, limited visualization of the distal foramen, and often generous epidural venous plexi and associated bleeding.⁵⁴ Furthermore, the muscle dissection often needed to obtain an adequate surgical exposure has been associated with increased postoperative muscle spasm, neck pain, and recovery time. When considering laminectomy, reported results tend to disagree. With respect to age, some investigators find a significantly better outcome in patients under 50, while others do not. Regarding general overall improvement, some studies reported benefit in over 80% of cases, whereas others found no significant advantage over conservative therapy. Finally, most authors agree that shorter duration of preoperative symptoms is a good prognostic factor, while some deny any significance. Possible confounding factors include the consideration of cases where osteophyte removal, opening of the dura, or sectioning of the dentate ligaments was performed concurrently with laminectomy (which tends to cause more complications due to neural injury). Despite the glaring differences, it is generally believed that younger patients who have less neurological involvement and a shorter duration of disease enjoy greater improvement.

Overall, clinical outcomes associated with the surgical treatment of degenerative disc disease by anterior cervical discectomy (ACD) or anterior cervical discectomy and fusion (ACDF) have been excellent. According to a literature review from 1991,⁵⁸ good clinical outcomes have been reported for 61% to 94% of ACDF cases and for 65% to 96% of ACD cases. These data showed that an interspace fusion is not mandatory for good clinical outcomes. The development of a fibrous union or pseudarthrosis has not been consistently associated with poor clinical outcomes. However, once pseudarthrosis is present, 67% of patients have associated symptoms.⁵⁹ Since then, the question of whether an interbody fusion is required has been unresolved.⁶⁰ Proponents of ACD favor its simplicity, low cost, and the absence of complications related to autograft harvest and interbody graft failure (e.g., graft extrusion, collapse, subsidence, and pseudarthrosis). Advocates of ACDF stress that foraminal decompression by interbody distraction, prevention of disc space collapse, and stabilization of cervical alignment are key advantages compared with ACD alone. The resorption of dorsal osteophytes has been attributed to fusion and immobilization of the segment. The postoperative incidence of neck pain has been reported to be smaller with fusion than without. Furthermore, the incidence of kyphotic deformity is thought to be higher if fusion is omitted. Comparative, prospective clinical studies between ACD and ACDF, however, failed to find a clinical benefit to ACDF.^61–68

Despite these findings, the overall trend in the United States and Canada has been toward increased application of anterior interbody fusion for the treatment of cervical degenerative disc disease.^69–71 Autograft from the iliac crest has usually been used for interbody fusion. However, its harvesting is associated with complications such as prolonged pain, cosmetic deformity, wound infection, hematomas, and peripheral nerve irritation or injury.

Unplated anterior cervical interbody fusion for degenerative disc disease has a higher tendency to fuse with autograft than allograft, sometimes with better clinical outcomes.^72–74 In contrast, other studies failed to demonstrate significant differences in radiological or clinical outcomes between allograft and autograft.^75–77 A meta-analysis of the literature comparing fusion outcomes of allograft and autograft for one- and two-level cervical interbody fusion without plating found a higher fusion rate for autograft and a lower incidence of graft collapse than for allograft. However, clinical outcomes were statistically similar.⁷⁸ A review of the literature failed to find allograft to be an adequate equivalent to autograft for anterior cervical interbody fusion.⁷⁹ However, the morbidity associated with autograft harvest was eliminated by the application of allograft. The possibility of transmitting infectious diseases like human immunodeficiency virus from tissues, including allograft, donated by a screened donor is exceptionally rare.^75,76

A prospective study of ACDF comparing autograft and biocompatible osteoconductive polymers found significantly less graft protrusion and intersegmental kyphosis in the biocompatible osteoconductive polymer group. However, this study failed to demonstrate incorporation or biodegradation of biocompatible osteoconductive polymers.⁸⁰ In a prospective, nonrandomized study, Senter et al. ⁸¹ compared the outcomes of autograft ACDF with ACDF with hydroxyapatite. Fusion with the latter was equal or superior to that with autograft alone. In prospective comparisons of autograft and xenograft, clinical and radiological data favored the use of autograft.^82,83

Recent prospective clinical trials of fusion with interbody titanium cages have found promising clinical results and radiological outcomes, with low rates of implant failure (e.g., backout and subsidence) or pseudarthrosis when compared with allograft or autograft. Even the fusion rates for cages are superior to those associated with autograft or allograft fusion.^84–86 Despite these recent data, some conclude that autograft remains superior to alternative interbody fusion materials.⁸⁷

In the early 1960s, Bohler⁸⁸ applied an anterior cervical plate and screw construct to treat traumatic instability of the spine. After his report, anterior cervical plate constructs were applied using bicortical, nonlocked, variable-angle screws for fixation.^89,90 However, hardware failure was common,⁹¹ and a unilateral locked, fixed-angle plate-screw anterior system was introduced by Morscher et al.⁹² in 1986 (Figure 24-10A).

FIGURE 24-10 A–C, A classic Morscher type constrained construct is seen with converging screws that are constrained to the plate to prevent inadvertent backout (A). More modern anterior cervical plates are also constrained but allow more variability of the screws in the form of rotation and translation to facilitate screw placement, as well as to optimize long-term load sharing (B, C).

A variety of unicortical locked, dynamic, fixed, or hybrid plate-screw systems are now available for anterior cervical interbody fusion and plating⁹³ to increase stability of the cervical fusion segment (Figure 24-10B,C). As a result, fusion rates have increased, and the rates of graft failure and pseudarthrosis have thereby decreased.^94,95 Furthermore, anterior cervical plate fixation for degenerative disc disease maintains sagittal balance more effectively,^96–98 thereby potentially limiting adjacent level biomechanical stress.⁹⁹ Postoperative loss of lordosis and cervical kyphosis have been associated with ACD and ACDF without plating. Yet, again, prospective randomized studies comparing single-level ACD, ACDF, and ACDF with plating have failed to show a clinical benefit associated with either procedure,^66,100 although a clinical benefit was found for two-level procedures.¹⁰¹ Moreover, concern has been expressed about the cost and complication of cervical plating for the treatment of degenerative disc disease. Hardware failure has been a source of early and delayed morbidity. In a prospective clinical trial, patients undergoing ACDF with plating tended to have a more frequent incidence of dysphagia than patients without plating. Yet, in the same study, more multilevel procedures were performed in the plating group, which could also account for these findings.¹⁰²

In more recent surgical series, refinements in the design of anterior cervical plating and more surgical experience have lowered the incidence of plate-related complications.^103–109 When all aspects, including possible reoperation and time to return to work, are considered, overall costs decrease when anterior cervical plating is added to fusion.¹¹⁰ Plating also may increase fusion rates with allograft and thereby obviate the need for autograft.¹¹¹The complications associated with autograft harvest would be decreased without compromising fusion rates. Again, experts are divided on the need for plating, in particular, for single-level disease.

Complications of Surgery

The complications of these procedures are similar to those of any other type of surgery, with a mortality rate of less than 1.5%. Cardiac disorders, thrombophlebitis (with possible pulmonary embolism), and infection top the list. Vessels exposed to injury are the vertebral arteries, the carotid arteries, and the jugular vein; extradural or superficial hematomas may also occur. Nerves at risk include the paravertebral sympathetic chains, the superficial and recurrent laryngeal nerves, along with the spinal cord and nerve roots. Soft tissue complications may involve surgical injury to the trachea, esophagus, thoracic duct, and cervical pleura (Figure 24-11A). Often, the recurrent laryngeal nerve is injured from a combination of the anterior cervical retractor blades compressing the nerve against the endotracheal tube itself, thereby resulting in injury to the mucosal portion (Figure 24-11B). Infection runs the gamut from easily treated to discitis (leading to severe, lingering pain) or meningitis (also a complication of dural injury).

FIGURE 24-11 A–B, The proximity of the recurrent laryngeal nerve [RLN] in relation to the trachea [T] and carotid sheath [CA] demonstrates the tenuous nature of this structure that can often be injured during anterior cervical approaches (A). The mucosal portion of the RLN can also be damaged by retraction of the midline structures causing the nerve to be sandwiched between the endotracheal tube and the retractor (B).

When comparing anterior and posterior approaches, neurological complications occur more commonly after laminectomy (2% to 8% of patients compared to the combined 1.04% average for both approaches). During the posterior procedure, displacement of the thecal sac and spinal cord after decompression can lead to cord or root damage. During the anterior procedure, bone grafts can result in displacement or nonunion. For iliac grafts, complications include donor site pain, hematoma, and infection, as well as possible injury to the lateral cutaneous nerve in the thigh.

Emerging Technologies: Artificial Disc Replacement

After cervical spinal fusion, increased motion has been documented at adjacent levels,¹¹² and radiological data have shown degenerative disc disease to occur at adjacent cervical segments on long-term follow-up¹¹³ (Figure 24-12A). Whether the increased incidence of adjacent level degeneration (ALD) found in the cervical spine after fusion is caused by increased mechanical stresses on adjacent cervical segments or whether the observed degenerative cervical changes merely represent the natural history of degenerative disc disease of the cervical spine is unknown. Clinical studies estimate that the incidence of symptomatic degeneration above a fusion ranges from 2% to 3% per year above the expected natural history¹¹⁴ (Figure 24-12B). The rationale underlying the use of artifical discs is to maintain physiologic segmental cervical motion after ACD and decompression of the neural structures. By maintaining cervical segmental motion, adjacent level motion is decreased.¹¹⁵ Theoretically, this decrease should eliminate or reduce the incidence of ALD. Several artificial discs have been designed and applied clinically. Short-term follow-up data have shown equivalent clinical outcomes when cervical degenerative disc disease is treated with conventional fusion or an artificial cervical disc.^116–118 Earlier designers of artificial cervical joints showed a more frequent incidence of hardware failure when compared with more recent clinical evaluations of cervical artificial joints. ^116–118 Placement of these discs is technically very similar to that of standard anterior cervical interbody grafting techniques. Authors describe the need for wider interbody exposure, discectomy, and more meticulous endplate preparation. Specific implantation techniques vary according to the specific design of the artificial disc. Whether these devices will be associated with superior clinical outcomes compared with standard surgical treatment options for cervical degenerative disc disease will only be determined when sufficient long-term follow-up data have been gathered from ongoing clinical trials in the United States and Europe.

FIGURE 24-12 A–B, Adjacent segment degeneration can occur after successful anterior cervical discectomy and fusion. This can occur either from stress and/or motion transfer to the adjacent levels (A) or directly from hardware impingement (B). This phenomenon can affect either the rostral or caudal level.

The BRYAN cervical disc (Medtronics; Minneapolis, MN) trial was published in 2009¹¹⁹ (Figure 24-13A). This was a multicenter study in which patients with single-level cervical DDD were randomized to receive either the BRYAN cervical disc (n=242) or anterior cervical discectomy and fusion (n=221).¹⁴ The main study hypothesis was that the outcomes from disc replacement would be at least equivalent to fusion. 465 patients were followed for two years. Initially, investigators and patients were blinded to the procedure. However, postoperatively, the investigational group was treated with a two-week course of nonsteroidal antiinflammatory drugs and was allowed to resume nonstrenuous activities as they pleased. Because of these postoperative differences, “further blinding was not practical or ethical.” At 24-month follow-up there was a 91.6% retention rate. At 24 months, both groups had improvements in the clinical outcomes. Overall success in the intervention group was 82.6% compared with 72.7% in the fusion group (p=0.005). Neck Disability Index (NDI) scores were 16.2 in the intervention group and 19.2 in the control group (p=0.025). NDI success (defined as greater than 15 point improvement in the NDI) was 86% in the intervention group versus 78.9% in the fusion group (p=0.001). Improvements in SF-36 scores were comparable, as were measures of neck and arm pain. Patients who received the BRYAN artificial disc returned to work about two weeks earlier than those who had fusion. Given that this was a non-inferiority trial, an as-treated analysis was the primary analysis (versus an intention-to-treat analysis). There were 12 patients in the study who were randomly assigned to receive the artificial disc but who received the control treatment because of anatomic or technique difficulties during the surgery. Another important limitation is that 117 patients were randomly assigned but declined participation once receiving the assigned treatment, many because of dissatisfaction with the assigned treatment.

FIGURE 24-13 A–C, Examples of the three approved artificial cervical disc prostheses demonstrate significant differences in design, materials, biomechanical range of motion, constraint, fixation type, and dampening ability to axial load. The BRYAN disc is impacted within the disc space and has rounded endplates to conform to the native disc endplates which have been premilled to match the metal contours. Small optional fixation pinholes are provided (A). The Prestige disc prosthesis relies on standard constrained body screws for fixation (B). The ProDisc-C utilizes two keels to maintain stability within the disc space (C).

The Prestige trial (Medtronics; Minneapolis, MN) was published in 2007¹²⁰ (Figure 24-13B). This was a multicenter trial in which 541 patients with single-level cervical DDD were randomized to cervical disc arthroplasty with the Prestige disc (n=276) or cervical fusion (n=265). Participants were not blinded. Overall success at 24 months was actually higher in the intervention group than in the control group. The NDI scores and NDI success were not statistically significantly different. The rate of neurologic success was greater in the intervention group. SF-36 scores and neck pain were improved more in the intervention group. There were fewer secondary surgeries in the intervention group.

The ProDisc-C (Synthes Inc; Paoli, PA) trial was published in 2009 and is the study upon which FDA approval was based¹²¹ (Figure 24-13C). This was a multicenter study at 13 clinical sites. A total of 209 patients were randomized to receive either the ProDisc artificial disc replacement (n=103) or ACDF (n=106). All participants had single-level cervical disc disease that was unresponsive to conservative treatment. All participants were blinded until after the surgery. The main study hypothesis was that the outcomes from disc replacement would be at least equivalent to fusion. A secondary hypothesis was that disc replacement was superior to fusion. All of the patients were followed for 2 years. The primary outcomes of overall success and NDI success were comparable in the two groups. Overall success was 72.3% in the intervention group versus 68.3% in the control group. The results of the secondary outcomes were comparable. Fewer secondary surgeries were required in the intervention group. Few patients in the disc replacement group required narcotics at follow-up (10.1% vs. 18.5%; p = 0.073). At 24-month follow-up, safety and efficacy were comparable in those who had disc replacement compared with those who got fusion.

In all three studies, the rate of adverse events was not inferior to those seen in the fusion group and was often less than those seen in the fusion group. Adverse events included device-related complications, esophageal dysfunction, surgical complications, and the need for secondary surgeries. Study follow-up was not long enough to determine the effect of disc replacement versus surgery on the rate of development of DDD in adjacent discs. The results of the three trials showed that cervical disc replacement was not inferior to cervical fusion based on 2-year clinical outcomes. The clinical outcomes evaluated are largely relevantal. Although the 2-year follow-up data are promising, they do not provide information about the long-term impact of these procedures. The theoretic advantage of a decrease in the development of adjacent disc DDD has not been shown over the long term. Thus, given the lack of information about the long-term clinical impact of artificial cervical disc replacement, whether or not the technology ultimately improves net operative and disease outcomes is not known.

Conclusion

Cervical spondylosis is a common degenerative disease resulting in pathological changes of the vertebrae, ligaments, joints, and soft tissues of the spinal column. Radiographic evidence of spondylosis has been demonstrated in at least 50% of patients over the age of 50. Pathophysiology includes a congenitally narrow canal, disc herniation, osteophyte formation, joint and ligament hypertrophy, and abnormal spine mobility. Cord injury is presumed to be either due to direct compression of neural elements, or compromise of vascular supply.

The clinical presentation of spondylosis can range from no symptoms to radiculopathy or severe myelopathy. Diagnostic imaging modalities include plain radiography and magnetic resonance imaging. Computed tomography with intrathecal contrast may play a role in evaluating certain disease processes poorly imaged by MRI. The role of neurophysiological testing with motor and somatosensory evoked potentials is not clearly defined, but may prove beneficial in measuring subclinical disease and predicting outcome following surgery. Conservative medical management is indicated for patients with minimal symptoms, with surgical intervention reserved for patients with significant disability and/or a progressive clinical course. Both anterior and posterior approaches with or without grafting and fusion have been described. Surgical outcome is variable and significant prognostic factors are not yet identified. The association between cervical degenerative disease and age suggests an increasing prevalence of cervical spondylosis as the elderly population expands. Understanding of cervical spondylosis is still limited and further research is necessary to better define criteria for patient selection for surgery, appropriate surgical procedures, prognostic factors, and outcome measures.