INTRODUCTION

Cervical spondylosis is a common, occasionally disabling condition that occurs as a consequence of the natural aging process that affects a large portion of the adult population. Symptomatic cervical spondylosis can be arbitrarily divided by the findings at initial presentation. These symptomatic patients present with axial neck pain, radiculopathy, myelopathy, or most commonly a combination of these symptom complexes.

This chapter will focus on the surgical treatment of cervical radiculopathy, specifically decompression of foraminal stenosis related to spondylotic changes. An initial review of the normal anatomy and pathologic changes responsible for the development of foraminal stenosis will be followed by a discussion on the clinical presentation and evaluation of these patients. The rationale, specific surgical techniques, potential complications, and clinical results of both anterior and posterior surgical approaches will be described in detail.

ETIOLOGY OF FORAMINAL STENOSIS

The cervical functional spinal unit consists of two vertebral bodies joined by an intervertebral disc anteriorly and two synovial facet joints posteriorly. The cranial surface of the vertebral body is typically concave from side-to-side and convex in the anteroposterior direction. The inferior surface is convex from side-to-side and concave in the anteroposterior direction. A projection on the lateral aspect of the superior surface of the inferior vertebral body is called the uncus. The uncus is intimately related to the convex lateral inferior surface of the cephalad vertebrae. This projection off the cephalad vertebral body is referred to as the enchanure or anvil. The ‘articulation’ between these two structures is referred to as the ‘uncovertebral joint’ or ‘joint of Luschka.’ Cervical nerve roots exit the spinal canal through the neural foramen in an anterolateral and inferior direction. The boundaries of the neural foramen are formed superiorly and inferiorly by the adjacent pedicles. The medial aspect of the facet joint and an adjacent portion of the articular column form the posterolateral border of the neural foramen. The anterolateral border is formed by the posterolateral portion of the uncus, the intervertebral disc, and the inferior portion of the superior adjacent vertebrae. Figure 61.1 shows a cervical spine model, viewed in an oblique projection, which illustrates the bony confines of the neural foramen.

Fig. 61.1 The bony anatomy of the neural foramen on an oblique view of a cervical functional spinal unit. The neural foramen is bordered superiorly and inferiorly by the adjacent pedicles. Anteriorly, the foramen is bordered by the uncovertebral joint, the intervertebral disc, and a portion of the vertebral body. The posterior margin of the neural foramen is composed of the facet joint and adjacent lateral mass.

Neurologic symptoms that arise from cervical spondylosis are the result of a cascade of degenerative events that likely begins in the intervertebral disc. Age-related changes within the disc lead to an alteration in the chemical composition of the nucleus pulposus. A decrease in the proteoglycan and water content in the nucleus alters the biomechanical properties of the disc itself, as well as those of the functional spinal unit. As a result, the disc loses height and bulges posteriorly into the spinal canal. The vertebral bodies physically move closer to one another as a result of the loss of disc height. This alteration in the normal anatomic relationships of the vertebral bodies, in combination with the altered biomechanical properties of the intervertebral disc, results in altered loading of the facet and uncovertebral joints. This increase in load through the facet and uncovertebral joints leads to the formation of osteophytes around these articulations and at the margins of the disc space.

Neural foraminal narrowing can occur as a result of both static and dynamic processes. Abnormal biomechanics that result from biochemical changes in the intervertebral disc may lead to microinstability that contributes to dynamic neural foraminal narrowing. Changes in the bony architecture of the borders of the foramen lead to static narrowing of the neural foramen. Posteriorly protruding disc material, uncovertebral osteophytes, or thickened soft tissues within the foramen may result in extrinsic compression of the nerve root. An oblique radiograph of the cervical spine illustrates the anatomic borders of the foramen and how uncovertebral joint osteophytes can result in narrowing of the foramen. Both Figure 61.1 and Figure 61.2 demonstrate how osteophyte formation from the facet joint could result in narrowing in the anterior–posterior dimension. The height of the foramen may also be compromised as the intervertebral disc loses its biomechanical integrity and loses height. As mentioned earlier, the vertebral bodies move closer together, causing the adjacent pedicles to move closer, thereby narrowing the cephalad–caudad dimension of the neural foramen. Surgical treatment of neural foraminal stenosis must address the anatomic structures that are responsible for narrowing of the foramen and may include an arthrodesis to eliminate any dynamic foraminal narrowing.

Fig. 61.2 An oblique radiograph of the cervical spine showing the anatomic borders of the foramen. This radiograph demonstrates how posterior uncinate process osteophytes can narrow the anterior–posterior dimensions of the foramen. Osteophyte formation of the facet joint can also affect the size of the neural foramen.

CLINICAL PRESENTATION AND PATIENT EVALUATION

Foraminal stenosis typically results in cervical radiculopathy which refers to symptoms that occur in a specific dermatomal pattern in the upper extremity. Patients typically describe sharp pain and tingling or burning sensations in the involved area. Diminished sensation and motor loss corresponding to the involved nerve root may be present, as may diminished deep tendon reflexes. Patients typically have neck and arm pain that prevents them from finding a comfortable position. They may find comfort by placing their forearm on top of their head, the so-called ‘shoulder abduction sign.’¹ Extension or lateral rotation of the head to the side of the pain (Spurling’s maneuver) may aggravate the symptoms. This finding may assist in the differentiation of radicular pain from other sources of shoulder pain and muscular neck pain. It is also paramount to remember that multiple sources of neck and upper extremity pain are extremely common and that neural compression may very well be occurring at two distinct locations.^2,³ Adaptations to the initial radiculopathy symptoms may result in secondary pathologic changes in the shoulder, carpal tunnel, and ulnar nerve that may cloud the clinical picture and persist long after the cervical radiculopathy has resolved. In a series of 736 patients with cervical radiculopathy treated operatively, Henderson et al. reported the clinical signs and symptoms at presentation. They found that 99.4% had arm pain, 85.2% had sensory deficits, 79.7% had neck pain, 71.2% had diminished deep tendon reflexes, 68% had motor weakness, 52.5% had periscapular pain, 17.8% had anterior chest pain, and 9.7% had headaches. The neurologic deficits at presentation correlated with the offending disc level in approximately 80% of the patients.⁴

As always, patient evaluation begins with a complete history and detailed physical examination. A complete neurologic exam of all four extremities should included motor and sensory examinations, as well as an assessment of deep tendon reflexes. Special attention should be given to the presence of pathologic reflexes in the lower extremities to rule out the possibility of coexistent myelopathy. Provocative tests such as Spurling’s maneuver should be performed. The presence of Lhermitte’s sign should be sought. Relief of radicular complaints with neck flexion and rotation away from the painful upper extremity may occur, as this motion opens the neural foramen. Similarly, direct axial cervical traction may lessen the radicular symptoms. In addition, it is necessary to assess for other etiologies of shoulder and/or arm pain such as peripheral nerve entrapment syndromes, intrinsic shoulder pathology, and vascular insufficiency.

Radiographic evaluation begins with plain cervical spine films in the anteroposterior and lateral projections. Oblique radiographs are at times helpful in assessing for foraminal narrowing from uncovertebral osteophytes, but are not routinely obtained. Dynamic (flexion–extension) lateral radiographs should be considered but are not necessary in every patient. Based on the patient’s presenting symptoms and history, the physical examination, and initial radiographs, the spine surgeon should have a good idea of what will be found on additional imaging studies or at the time of surgery. The decision to proceed with further imaging or diagnostic testing should be made by the surgeon based on the suspected diagnosis, the duration and severity of the symptoms, and other individual patient factors.

Additional studies that should be considered include bone scan, myelography combined with computed tomography (CT), electrodiagnostic testing, and magnetic resonance imaging (MRI). Consideration for bone scans should be given in patients with suspected malignancy, infection, or occult trauma realizing that bone scan may be normal in the setting of multiple myeloma. Myelography combined with computed tomography was the study of choice for the evaluation of suspected cervical stenosis until the widespread availability of MRI. Myelo/CT studies are still useful in those patients with contraindications to MRI and in potential revision situations. MRI has become the gold standard imaging modality for evaluation of patients with cervical radiculopathy and myelopathy. The advantages of MRI are that it provides complete visualization of the vertebrae, intervertebral discs, nerve roots, subarachnoid space, and spinal cord, including any intraspinal cord pathology. Multiplanar images are also routinely generated by this noninvasive, readily available imaging modality. It provides exquisite sensitivity in detecting subtle anatomic abnormalities. Axial images at the level of the neural foramen provide excellent contrast between the cerebrospinal fluid (CSF)-filled nerve root sleeve and the surrounding bony and soft tissue structures. Foraminal narrowing from disc herniation, uncovertebral osteophyte, facet hypertrophy, and in-folded ligamentum flavum can be visualized on these axial T2 images. An example of foraminal stenosis caused by uncovertebral osteophytes can be seen in Figure 61.3.

Fig. 61.3 T2-weighted axial MRIs demonstrating normal-appearing intervertebral foramen (A) and bilateral neural foraminal narrowing from uncovertebral joint osteophytes (B).

SURGICAL DECOMPRESSION OF FORAMINAL STENOSIS

Patients presenting with symptoms of cervical radiculopathy and imaging studies that coincide with the physical exam findings should be considered for active treatment. Medical rehabilitation and interventional spine treatment modalities including nonsteroidal antiinflammatories, mild narcotic analgesic medications, physical therapy, cervical epidural steroid injections, and selective nerve root blocks should be utilized initially for most patients. Absolute indications for surgical decompression of isolated foraminal stenosis are lacking although patients presenting radicular symptoms in combination with progressive myelopathy should be treated surgically. Strong indications for surgical intervention include profound muscle weakness and atrophy. Surgical decompression should also be considered if a patient has undergone a prolonged period of conservative management without resolution of their symptoms. A trial of 6–12 weeks of nonoperative modalities is considered adequate by most surgeons. The severity of the patient’s pain and the degree of muscle weakness play a role in the decision to abort conservative treatment and proceed with surgical intervention.

Once the decision has been made to treat a patient surgically, the surgeon is faced with the decision as to which approach is most suitable given the patient’s symptoms and the exact etiology of the foraminal narrowing. Anterior and posterior surgical approaches for foraminal stenosis have been described and excellent results have been reported with both. In general, patients with axial neck pain should be treated with anterior discectomy and fusion. Motion-sparing procedures such as posterior foraminotomy may not address alternative axial pain generators, such as the intervertebral disc and facets. Patients with isolated radicular symptoms may be treated with any of the above-mentioned procedures. Reports of excellent results with all procedures can be found in the literature. The theoretical advantages of each of the approaches will be discussed in the following sections of the chapter.

ANTERIOR CERVICAL DISCECTOMY AND FUSION

The anterior approach to the cervical spine allows for direct access to the compressive pathology responsible for foraminal stenosis. Bulging or herniated disc material and uncovertebral osteophytes lie anterior to the spinal cord and the nerve roots and can therefore be directly removed from an anterior approach. Figure 61.4 shows how these offending anterior structures are directly accessible for removal via an anterior approach. Robinson and Smith initially described anterior cervical discectomy and fusion in 1955.⁵ The anterior approach avoids direct manipulation of the neural elements. This original procedure relied on indirect decompression of the spinal cord and neural foramen by distraction of the disc space. Progression of spondylotic spur formation was prevented by stabilization of the segment and the authors believed that regression of these osteophytes occurred as a result of the arthrodesis. In 1958, Cloward published an alternative technique for anterior cervical discectomy and fusion in which direct decompression of the neural elements was performed.⁶ There are no comparative studies in the literature to support the clinical superiority of direct or indirect decompression of the neural elements in spondylotic radiculopathy. Individual surgeons must make a decision as to which philosophy they subscribe. The surgeon’s training as well as personal experience likely influence this decision.

Fig. 61.4 Axial T2 MRI images demonstrating the location of the offending structure, in this case a disc herniation, anterior to the spinal cord. Direct removal of this pathology can be accomplished, safely, via an anterior approach. Manipulation of the spinal cord would be necessary to directly remove this pathology from a posterior approach.

Numerous modifications of the original Smith–Robinson and Cloward bone grafting techniques have been described. The Smith–Robinson technique involves an autogenous tricortical corticocancellous horseshoe graft placed into the evacuated disc space. The cortical component of the graft provides structural support that maintains the disc-space height while the cancellous portion facilitates graft incorporation. The original technique involved simply removing the cartilaginous endplate and incomplete decortication. More aggressive decortication, beyond simple cartilaginous endplate removal, has been demonstrated to improve fusion rates.^7,⁸ Cloward’s autogenous graft was harvested from the iliac crest with an oversized hole saw. The oversized dowel graft was then impacted into an undersized hole at the level to be fused. The unicortical surface of this dowel graft was placed anteriorly, resting just posterior to the anterior surface of the vertebral bodies. Bailey and Badgley described a technique in which a ‘keystone-shaped’ corticocancellous graft was utilized.⁹ This trapezoidal-shaped graft is mortised into the prepared disc space. Excellent results with this technique were reported by Simmons in 1969.¹⁰

Contemporary choices for graft material include autograft, allograft, and synthetic cage devices. Good results have been reported with all of these graft choices when utilized for one-level discectomy and fusion without instrumentation, although the current literature does not support the superiority of any one single graft material or device.^7,¹¹^–¹⁵ Higher rates of radiographic arthrodesis have been reported with the use of autogenous iliac crest grafts, especially with multiple-level discectomies.^12,¹⁶ Higher radiographic fusion rates with autogenous grafts do not occur without consequences. Complications related to graft harvest include hematoma formation, infection, injury to the lateral femoral cutaneous nerve, iliac wing fractures, and, most importantly, persistent iliac crest pain have been reported.^17,¹⁸ Silber et al. reported iliac crest graft site harvest complications in a series of patients undergoing one-level anterior cervical discectomy and fusion (ACDF). Twenty-six percent of patients reported chronic pain at the donor site and nearly half of these chronically used pain medications. They also report functional impairment in 13% of the patients studied.¹⁷

Allografts have been used in anterior cervical spine surgery since the 1950s. Cloward reported a 94% fusion rate in 44 patients who underwent ACDF with a dowel-shaped, frozen allogeneic iliac crest graft.⁶ Schneider utilized freeze-dried allogeneic iliac crest bone for ACDF with the Cloward technique. He reported an arthrodesis rate of 93% with one-level procedures and an 85% fusion rate for multiple-level discectomy and fusion.¹⁹ The use of allograft iliac crest grafts with the Smith–Robinson has also been reported in the literature. Rish reported a fusion rate of 80% in single-level and 69% in multiple-level patients undergoing a Smith–Robinson-type ACDF with freeze-dried allogeneic iliac crest.²⁰ A 94% fusion rate was reported by Brown et al. in patients undergoing the same procedure with allogeneic, frozen iliac crest grafts.²¹ They also reported a high rate of graft collapse when allogeneic iliac crests are used. As a result of concerns over the compressive strength of allograft iliac crest grafts, some authors began utilizing fibular allograft for anterior cervical discectomy and fusion. Martin et al. reported on 289 patients who underwent ACDF with freeze-dried fibular allograft without instrumentation.¹¹ Radiographic fusion was obtained in 90% of those undergoing one-level fusions. After two-level procedures, only 72% showed radiographic fusion at all levels. Although there was a trend towards higher rates of nonunion in those patients who were smokers, the difference was not statistically significant. The authors concluded that freeze-dried allogeneic fibula is an effective substrate for obtaining fusion following anterior cervical discectomy without instrumentation.

In an attempt to increase the likelihood of solid arthrodesis, many authors have advocated the addition of an anterior cervical plate, especially for multiple-level procedures. Radiographs of a two-level anterior discectomy and fusion with an anterior cervical plate are shown in Figure 61.5. Instrumentation increases the stability across the operative segment and decreases the motion between the graft and vertebral endplate, thereby increasing the chance of solid arthrodesis. The addition of anterior cervical instrumentation has been shown to decrease the rate of pseudoarthrosis in both single and multiple-level ACDFs. Nonunion rates ranging 11–63% have been reported depending on the number of levels at attempted fusion, the type of graft material used, and whether or not anterior instrumentation was utilized.^12,²²^–²⁵

Fig. 61.5 Lateral and anteroposterior radiographs of a patient who underwent a two-level anterior cervical discectomy and fusion with autogenous iliac crest bone graft. An anterior cervical plate was utilized to increase the immediate stability of the construct and to increase the likelihood of solid arthrodesis.

Wang and colleagues reviewed the clinical and radiographic results of 80 patients treated with single-level ACDF.²⁶ Pseudoarthrosis rates of 4.5% and 8.3% were reported for instrumented and noninstrumented, respectively. Patients stabilized with an anterior plate had significantly less graft collapse and kyphosis than those without a plate. The clinical outcomes based on Odom’s criteria were not significantly different between the two groups. In two separate reports, the same senior authors have also reported retrospectively on the use of anterior cervical plates in two- and three-level ACDFs.^27,²⁸ Autogenous tricortical iliac crest grafts were used in all patients in each study. In the review of two-level procedures, a statistically significant difference in pseudoarthrosis rate was found in the instrumented group (0%) compared to the noninstrumented group (7%).²⁷ The use of a cervical plate did not alter clinical outcomes but those patients who developed a pseudoarthrosis had poorer clinical results. In the third report by this group, the results of three-level ACDF were reviewed.²⁸ Forty of the fifty-nine patients were stabilized with an anterior cervical plate. Pseudoarthrosis developed in 18% (7/40) of the plated patients and 37% (7/19) of those treated without a plate. This difference was not statistically significant, perhaps because of the small number of patients, but the authors point out that the rate of nonunion in the noninstrumented group is nearly twice that of the instrumented group. Once again, the development of a pseudoarthrosis resulted in poorer clinical outcomes.

Other groups have analyzed the results of both one- and two-level ACDFs treated with and without plates.^29,³⁰ Caspar et al. retrospectively reviewed the charts of 356 patients who underwent one- and two-level ACDF with and without anterior instrumentation for degenerative disorders.³⁰ Six percent of those undergoing noninstrumented fusions required reoperation for pseudoarthrosis compared to 0.7% in whom an anterior cervical plate was used. Two (out of 146) patients in whom a plate was used required a revision procedure secondary to hardware failure prior to fusion. The authors concluded that the use of anterior instrumentation for one- and two-level ACDFs results in a significant reduction in reoperation rates. In a retrospective manner, Kaiser et al. compared the radiographic results of a group of patients stabilized with anterior cervical plates following one- and two-level ACDF with a historical cohort of patients that were treated without plates.²⁹ Cortical ring allograft struts were utilized in each of the groups. The fusion rates for one- and two-level ACDF with anterior instrumentation were 96% and 91%, respectively. Significantly lower fusion rates were found in those one- and two-level procedures (90% and 72%, respectively) that were not stabilized by an anterior plate.¹¹ No infectious, neurologic, or graft-related complications were reported in the instrumented group. Statistical analysis revealed a higher graft complication rate in the noninstrumented group from the historical cohort. The authors conclude that the improved fusion rates and negligible complication rates justify the routine use of anterior cervical plating in the treatment of cervical spondylosis.