Treatment Evolution in Management of Cervical Disc Disease

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Chapter 151 Treatment Evolution in Management of Cervical Disc Disease

Cervical disc disease may be more neurologically compromising due to anatomic particularities than the more frequently occurring lumbar disc disease. However, cervical degenerative disc disease is the most common cause of acquired disability in patients over the age of 50.¹ Despite this, there is a lack of firm evidence regarding the surgical options and prognostic factors associated with its management.²

Since their first description, together with their typical signs and symptoms, the operative therapy of cervical disc disease has undergone an evolution. The frequent shifts of paradigms in treatment are particularly noticeable compared to other neurosurgical diseases. The trend of using smaller operative corridors is seen according to the basic tenet of neurosurgery: to effectively treat pathology with minimal disturbance of normal anatomy. Here, various anatomic characteristics of the cervical spine and its degenerative disc pathologies imply limited choice of approach and techniques. This choice fed for several decades the ongoing discussion and main controversies about whether to address cervical degenerative disc pathologies from an anterior or a posterior approach and whether any implantation of devices or even fusion is necessary.

Originally, the dorsal decompression of neural structures with a generally invasive posterior approach was the primary aim of the operation. Because of anatomic limitations, a shift of paradigm favored an anterior approach and discectomy, without and with implantation of various spacers, in the middle of the last century. Large variety in the materials and designs of these implants, as alternatives to autologous iliac crest bone, was established, with the aim of solid fusion of the operated segment. Anterior cervical discectomy with fusion (ACDF), regarded worldwide as the gold standard for the treatment of cervical disc disease, was further complemented by modified, minimally invasive, or endoscopic techniques using anterior and posterior approaches. The fear of adjacent-level disease in the vicinity of a fused cervical segment led to another shift of paradigm in recent years: away from fusing procedures, toward motion preserving new technologies, and back to minimally invasive dorsal techniques in the treatment of cervical disc disease.

In this chapter, the evolution of the operative treatment of cervical disc disease in the last 80 years is reviewed; the advantages, disadvantages, and techniques of each approach are outlined; and the rationale of the shift of paradigms is focused on. Furthermore, alternative and future treatment concepts are illuminated.

Historical Development

In 1543, the anatomist and surgeon Andreas Vesalius (1514-1564) was the first to describe the intervertebral disc. However, its role in the development and as cause for various clinical signs and symptoms was not recognized until about 80 years ago. In 1928, Stookey ³ reported on several clinical syndromes evoked by herniated cervical discs but interpreted the prolapse as “chondroma or neoplasm of the notochord.” Primarily, investigations by Schmorl⁴ in Europe and Keyes and Compere⁵ in the United States contributed to a detailed understanding of the pathophysiology of the intervertebral disc. Shortly after these investigations, Mixter and Barr⁶ clearly associated a lumbar disc prolapse with the signs and symptoms of nerve root compression; the alterations of the cervical intervertebral discs were identified as reason for neck pain, radiculopathy, and myelopathy.

Historically, the routine surgical approach for symptoms produced by cervical disc disease was posterior. During the last half of the last century, it became clear that the main problem of this approach was the technical challenge of displaying and removing compressive structures that lie anterior to the spinal cord and nerve roots. This need for easier access to reach anterior compressing structures led to the development of an anterior surgical approach to the cervical spine. Bailey and Badgley ⁷ performed the first anterior stabilization of the cervical spine on a lytic process in 1952 and published their technique in 1960. In 1955, Robinson and Smith⁸ describe their method to stabilize a pathologically changed cervical spine segment using a horseshoe-shaped iliac bone graft. Without knowledge of the results of the other investigators, Cloward⁹ published his technique of anterior discectomy for removal of compressing structures in 1958.

Since that time, a multitude of variations and modifications have been done in the treatment of degenerative cervical disc disease. Different approaches are competing, as well as numerous implants, varying mainly in material and design. However, the crucial question of “to fuse or not to fuse” has not yet been answered. It is still a controversial issue if a favorable outcome can be achieved by decompression followed by solid fusion or if microsurgical decompression or decompression with arthroplasty can provide long-term preservation of motility.

When conservative therapy fails or progressive neurologic deficits are imminent, it comes to a decision for operative treatment. However, the decisions about what approach and what technique to use have to take a large number of variables into consideration. In the following section, the treatment evolution in operative management of cervical disc disease is illuminated and discussed, taking aspects such as approaches and techniques, indications, complications, advantages and disadvantages, and biomechanical consequences into account.

Laminectomy and Laminoplasty

Initially, the routine surgical approach for symptoms produced by cervical disc disease was posterior. Mixter and Barr ⁶ published their report, which described the use of laminectomy to treat 19 cases of intervertebral disc herniation, including four ruptured cervical discs, in 1934. Since then, posterior approaches and techniques evolved from laminectomy into small keyhole foraminotomy and various laminoplasty methods.

The main indication for laminectomy in degenerative cervical disc disease is single- or multilevel stenosis of the spinal canal caused by various types of pathology, including spondylosis and ossification of the posterior longitudinal ligament, usually presenting with myelopathy or radiculomyelopathy. Laminectomy is preferably employed for patients over 65 years of age who demonstrate variable ventral pathology but with multilevel spondylosis and stenosis in the presence of a well-preserved cervical lordotic curvature. In addition, a medial facetectomy and foraminotomy can be performed at the necessary levels to address a specific disc herniation and spur.¹⁰

Open posterior approaches to the cervical spine with laminectomy avoid the approach-related complications associated with anterior approaches but require extensive subperiosteal stripping of the paraspinal musculature, which often results in significant postoperative pain. Moreover, accelerated degeneration of adjacent motion segments after anterior fusion, or so-called adjacent segment disease (ASD), is avoided.¹¹ Nevertheless, apart from anatomic limitations in reaching centrally or paracentrally located soft discs from this approach, long-segment decompression in patients who experience a preoperative loss of lordosis increases the risk for postoperative sagittal plane deformity.¹²

Complications after laminectomy include a 0% to 10% incidence of spinal cord injury and up to a 12.8% frequency of root injury.¹⁰ Nerve root deficits, typically involving C5, are variously attributed to direct mechanical manipulation or to “tethering” of the root after rapid cord decompression and dorsal migration after laminectomy.¹³

Laminectomy is successful in 77% to 85% of patients, while 10% to 15% may acutely deteriorate and another 23% exhibit delayed deterioration over 10 or more years.¹⁴ Rodrigues¹⁵ analyzed 51 patients who underwent laminectomy and disc removal for the treatment of paramedian and posterolateral soft cervical disc herniation and noticed 96% total relief of pain, 76% motor improvement, and 63% sensory improvement.

The clinical long-term outcome after cervical laminectomy,¹⁰ as well as the biomechanical alterations induced by multilevel cervical laminectomy,¹⁶ have been analyzed frequently. Performing extensive multilevel laminectomies typically does not immediately destabilize an otherwise intact spine¹⁷ but rather results in denervation and atrophy of the posterior cervical muscles. In addition, surgery denervates and disturbs the facet joints and the loss of the posterior tension band increases the force on the anterior vertebral body, which in turn worsens the sagittal deformity and results in a kyphotic angulation.

Several strategies have been used to prevent postoperative sagittal deformity after multilevel laminectomies. One option involves posterior segmental instrumentation and fusion performed at the time of the initial surgery. This adds considerable time and morbidity to the operation,¹⁸ results in a substantial decrease in mobility, and subjects adjacent levels to larger stress and accelerated degeneration. Another option includes laminoplasty or osteoplastic laminotomy. Because of concerns over complications of nonfusion-related laminectomy (spinal deformity, instability, compression by “laminectomy membrane,” and late neurologic deterioration), laminoplasty was developed in Japan in the 1970s as an alternative to laminectomy.¹⁹ A variety of laminoplasty techniques have been described; in all, the laminae are preserved, but the size of the spinal canal is expanded because the freed or partially freed laminae are positioned more posteriorly (Fig. 151-1).

FIGURE 151-1 Postoperative three-dimensional computed tomography (CT) scan after four-level cervical laminoplasty.

In their critical review on cervical laminoplasty, Ratliff and Cooper ¹⁹ found no difference in neurologic outcome based on different laminoplasty techniques or when laminoplasty is compared to laminectomy. Furthermore, there was no benefit to laminoplasty over laminectomy in adult patients in terms of spinal alignment, incidence of kyphotic deformity, and the development of the postlaminectomy membrane. Cervical range of motion (ROM) decreased substantially after laminoplasty, with progressive loss in long-term follow-up studies and final ROM similar to that seen in patients who had undergone laminectomy and fusion. This gradual laminoplasty-induced decrease in cervical ROM may allow for gradual compensation by adjacent segments, thus limiting adjacent-segment disease.

Some studies compare the long-term outcome after laminoplasty and anterior spinal fusion for cervical radiculomyelopathy due to soft disc herniation ²⁰ and for multilevel myelopathy.²¹ Because the two procedures provided the same neurologic improvement, the risks of bone graft complication with the anterior approach must be weighed against the risks of chronic neck pain associated with laminoplasty for determining the best technique. Furthermore, the posterior technique in this context may be reserved for multilevel soft disc herniation in older and multimorbid individuals.

The feasibility of minimal invasive access multilevel laminectomy and laminoplasty techniques were first shown in cadaver models.²²^–²⁴ Both techniques showed a 43% expansion of the cross-sectional areas of the spinal canal. In a clinical study on 10 patients with degenerative compressive myelopathy treated with endoscopic partial laminectomy, Yabuki and Kikuchi²⁵ showed that the technique was safely practicable and that all patients experienced symptomatic improvement. Furthermore, due to less muscle trauma and preservation of much of the normal osteoligamentous anatomy of the cervical spine, the postoperative wound pain and the risk for postlaminectomy kyphosis was reduced. Perez-Cruet ²² reported on four patients with minimally invasive cervical laminoplasty and satisfactory postoperative neurologic improvement. Technically feasible, the author noted technical difficulties associated with elevation of the lamina and insertion of bone grafts due to the limited approach.

Posterior Foraminotomy

The posterior foraminotomy was pioneered by Frykholm ²⁶ and Spurling and Scoville²⁷ and later modified by Scoville et al.²⁸ Accessible pathologies are laterally located, soft disc herniation and foraminal stenosis (hard disc), usually presenting with radicular symptoms (Fig. 151-2). Posterior foraminotomy may be performed unilaterally at one or more levels, bilaterally at one or more levels, or in combination with a laminectomy or laminoplasty.¹⁰ The detailed technique has been described elsewhere.^10,²⁹ A major benefit of posterior foraminotomy versus posterior and anterior techniques with fusion is the preservation of stability and mobility. The avoidance of approach- and graft-related complications, impending in anterior techniques, is another important advantage. Limitations are the removal of compressive structures that lie anterior to the spinal cord and nerve roots.

FIGURE 151-2 (A) Axial magnetic resonance image showing a soft disc prolapse, and (B) CT scan showing a foraminal stenosis, both suitable for posterior foraminotomy.

Numerous publications focus on the indications, advantages, and long-term outcome of patients with lateral cervical soft disc herniation or osteophytes (foraminal stenosis), treated with posterior (keyhole) foraminotomy.³⁰^–³³ Successful relief of radiculopathy symptoms are seen in 90% to 98%, with complication rates between 0% and 4%, and recurrence rates of 0% to 6%.

Limiting the degree of medial facetectomy to less than 50% prevents postoperative instability ³⁴ (Fig. 151-3). Because fusion is not applied, concerns about associated morbidity and the later development of adjacent-level disease theoretically are relatively minor. Nevertheless, Clarke et al. found in 303 patients with cervical radiculopathy, who were treated with posterior foraminotomy between 1972 and 1992, development of symptomatic adjacent-level disease in 4.9% after a mean follow-up of 7.1 years.³⁵

FIGURE 151-3 (A) Pre- and (B) postoperative CT scan after posterior foraminotomy, depicting the amount of bone removal.

Posterior cervical microendoscopic foraminotomy (MEF) and discectomy are the endoscopic alternative of microsurgical “open” posterior foraminotomy. The alternative was developed to address cervical nerve root compression by direct visualization of pathologic findings while minimizing tissue destruction and exposure. Muscle and ligamentous attachments to the spine are preserved, thus decreasing postoperative pain and spasm and helping maintain long-term stability.³⁶ Initial cadaveric studies using this technique demonstrated that the average vertical and transverse diameters of the laminotomy defect were identical for the MEF or open technique.³⁷ The average amount of facet removed and the length of neural decompression were greater with MEF than with the open approach. Initial clinical results have been quite favorable for the MEF procedure.³⁸ Operative times, blood loss, length of hospitalization, and need for postoperative pain medications have all generally been reduced when MEF is used, compared with the open procedure, yielding equivalent clinical results.^11,^39,⁴⁰ However, MEF is technically demanding, has a steep learning curve, and may require training within a cadaver laboratory.³⁶

Anterior Discectomy, Arthrodesis, and Arthroplasty

Anterior cervical discectomy (ACD) for spinal cord or nerve root compression was first described independently by Cloward,⁹ and by Smith and Robinson⁴¹ more than 50 years ago. Evolved from posterior techniques due to limited anatomic access, the common feature of this technique is the substantial or complete removal of the disc. Recently, anterior cervical foraminotomy was introduced,^42,⁴³ which reduces the extent of disc removal but still has the anterior approach. The anterior approach to the cervical spine generally implies several approach-related complications (recurrent laryngeal nerve palsy, dysphagia, and esophagus and hypopharynx perforation)⁴⁴^–⁴⁶ that do not exist in posterior approaches. In his systematic review using evidence-based medicine to identify the best techniques for anterior cervical nerve root decompression, Matz⁴⁷ concluded that ACD, ACDF, and arthroplasty are effective techniques for addressing surgical cervical radiculopathy. However, the controversial question in recent decades has been, “Does anything have to be inserted in the empty disc space after anterior decompression,^48,⁴⁹ and if so, what is the ideal implant/cage material and design for that?”^50,⁵¹ More questions have arisen, focusing on required additional anterior instrumentation and whether it might not be better to replace arthrodesis by arthroplasty.

Anterior Discectomy without Graft

In 1958, Cloward ⁹ first introduced the concept of ACD without fusion and direct surgical decompression of dorsal osteophytes. Anterior removal of the cervical disc is an effective and reliable treatment for nerve root or cord compression caused by disc herniation or spondylosis. Although physicians have traditionally included fusion as a part of this procedure, recent experience has suggested that this may not be necessary. The majority of published data focusing on ACD date from the 1970s to the 1990s.^48,⁵²^–⁵⁵ Sonntag and Klara⁵⁶ express opposing views on the need for fusion after discectomy: Sonntag believes that the majority of patients are well served with discectomy alone, avoiding the complications of graft harvest and potential nonunion. Klara feels that the interposed graft restores foraminal height and maintains cervical lordosis, both of which are important to a good outcome.

Of 64 patients with radiculopathy and/or myelopathy treated with ACD between 1994 and 1998, Donaldson and Nelson ⁵⁷ found a 91% success rate after a mean time of follow-up of 8.5 months. In a multicenter, prospective, randomized, controlled study, Oktenoglu et al.⁵⁸ operated on 11 patients, applying simple anterior microdiscectomy technique, and on 9 patients via ACD and fusion with a semirigid plate technique. Satisfactory results were achieved in both groups. However, although fusion with a semirigid plate preserved disc height and neural foramen height at the operated level in the immediate postoperative period, it did not stop subsidence permanently.

Haden et al.⁵⁹ conducted a prospective, observational cohort study to investigate the relationships among loss of disc height, cervical spine alignment, and clinical outcome in 140 patients undergoing ACD without interbody graft or cage. At a minimum of 12 months, there was no relationship between loss of disc height and outcome. Loss of the overall cervical lordosis was present in 71 patients, and segmental kyphosis was found in 69 patients. Analysis of clinical outcome showed no significant differences between patients with preserved and abnormal cervical alignment. Neither loss of disc height nor disturbance of cervical alignment compromised clinical outcome in the first year following ACD.

Anterior Discectomy with Fusion

Data from a nationwide survey on the contemporary practice of spinal fusion in the United States ⁶⁰ indicate that cervical spinal fusion experienced a rapid increase in utilization between 1993 and 2003. These changes are more pronounced for patients over 40 years of age and for degenerative disc disease. Similar preferences were seen among Canadian surgeons⁶¹ concerning the treatment of single-level cervical degenerative disc disease causing radiculopathy and/or myelopathy. Fusion was employed 93% of the time following ACD, with autologous bone as fusion material in 76% of cases. Additional anterior plating was added in 42% of ACDF cases. Posterior techniques were not mentioned. In a comparable survey among 22 orthopedic surgeons and 8 neurosurgeons within the United States about variation in decision making,⁶² the greatest agreement occurred for single-level disc herniation, with all surgeons choosing an anterior discectomy and 28 of the 29 respondents recommending fusion.

A number of neurosurgeons ^7,⁶³ recommended fusion of the involved segment without decompression of the spinal canal from dorsal osteophytes more than 50 years ago. After immobilization of the degenerated segment, resorption of dorsal osteophytes was documented.⁶³ Autograft from the iliac crest has mostly been used for interbody fusion.^64,⁶⁵ However, harvesting of autologous bone is associated with complications such as prolonged pain, cosmetic deformity, wound infection, hematomas, and peripheral nerve irritation or injury.^46,^66,⁶⁷ Therefore, alternative interbody implants were sought.

Cloward ⁹ first successfully used allograft for cervical interbody fusion, and allograft became one of the most frequently used interbody implants in the United States.⁴⁹ Anterior cervical interbody fusion for degenerative disc disease has a higher tendency to fuse with autograft than allograft and shows better clinical outcomes according to one study,⁶⁸ but other reviews fail to demonstrate significant differences in clinical or radiologic outcomes.⁶⁹ However, the morbidity associated with autograft harvest was eliminated by the application of allograft.

Polymethyl methacrylate (PMMA) was introduced in the 1960s as an interbody spacer for degenerative disc disease of the cervical spine ⁷⁰ (Fig. 151-4). This material is easy to handle, is inexpensive, and has been used until recently, despite some skepticism, mainly in the Western European community.⁷¹^–⁷⁴ Various other materials applied include ceramics (hydroxyapatite and tricalciumphosphates,^75,⁷⁶ carbon fiber cages,^77,⁷⁸ titanium cages^79,⁸⁰ (Fig. 151-5), polyetheretherketone (PEEK) cages⁸¹ (Fig. 151-6A), Bagby and Kuslich cages,⁸² and bioresorbable cages.⁸³ These cages show substantial differences not only in material used but also in design⁸⁴ and thereby in their biomechanical properties (subsidence, primary stability, and dislocation). Preferably, in ceramic materials, supplements of osteoinductive substances, like bone morphogenetic protein,⁸⁵ have been added to promote intervertebral bone matrix formation.

FIGURE 151-4 (A) Lateral radiograph after PMMA interposition. (B) Sagittal and (C) axial CT scan 13 years after PMMA interposition, showing fusion by bone formation around the interbody spacer.

FIGURE 151-5 (A) Lateral radiograph, (B) sagittal, and (C) axial CT scan 7 years after titanium cage interposition and fusion.

FIGURE 151-6 Lateral radiographs (A) after PEEK cage interbody fusion C3-C4 and C5-C6 and (B) after ACDF and plating C5-C6.

The efficacy and outcome after ACD, ACDF, and posterior foraminotomy for the treatment of cervical radiculopathy have been compared in several prospective and retrospective studies.^73,⁸⁶ Wirth et al.⁸⁶ found all three procedures equally successful for treatment of radiculopathy caused by a herniated cervical disc. In addition, they saw a trend for higher recurrence at the same level with posterior foraminotomy and recurrence at other levels with ACDF. Another retrospective study on 292 patients with monoradiculopathy, treated either with posterior foraminotomy or ACDF, showed similar results after 72.1 months.⁷³ Although the success rate was higher in the ACDF group (93.6%) than in the foraminotomy group (85.1%, P < 0.05), complications related to surgery occurred more frequently in the ACDF group (6.5%) than in the foraminotomy group (1.8%, P < 0.05).

Anterior Discectomy with Fusion and Plating

After anterior instrumentation with a plate and screws was introduced for the treatment of traumatic cervical instability in the 1960s,⁴⁹ the combined use of auto- or allograft and other cages and plating for fusion after decompression of cervical degenerative disc disease became an attractive option that has gained increasing popularity among spine surgeons and neurosurgeons (Fig. 151-6B). The use of internal fixation with plates attempts to increase the fusion rate and preserve or restore segmental lordosis in the affected cervical spine segments. In addition, the period and extent of immobilization after ACDF is reduced, the risk of graft extrusion is minimized, and donor site morbidity can be eliminated by the use of allografts. With all these advantages, Yue et al.⁸⁷ found no radiologic and clinical compromise in their 5- to 11-year follow-up study. Similar results are found when other cage materials are used, in addition to plating.^76,^88,⁸⁹ However, osteoinductive recombinant human bone morphogenetic protein-2 has been added safely and effectively in such constructions to enhance and accelerate fusion.⁹⁰

Recently, bioabsorbable anterior cervical plating ^91,⁹² achieved fusion rates similar to those previously reported in the literature with metallic implants and was superior to noninstrumented fusion. The bioabsorbable polymer plate and screws appear to be well tolerated by the patients. In a prospective, randomized study on 42 patients with cervical radiculopathy, the 2-year outcome after ACD, ACDF, or ACDF with plating was analyzed.⁹³ The technique of reconstruction played no role in clinical results, while ACD alone resulted in segmental kyphosis compared to ACDF and ACDF with plating. The authors concluded that patient selection and surgical decompression remain the keys to achieving desirable clinical outcomes after cervical discectomy for radiculopathy.

Anterior Foraminotomy and Endoscopic Foraminotomy

Similar to posterior techniques, getting less invasive and establishing the use of the endoscope, an alternative has been adopted increasingly for anterior procedures in recent years. Anterior cervical foraminotomy was developed under the concept of “functional spine surgery,”⁴² which directly eliminates compressive pathologic factors while preserving functional anatomic features, thus preventing the acceleration of adjacent-level degeration.⁴³ In current series,^42,^43,⁹⁴ good and excellent results were seen in 91% to 98% of cases, with few complications and high preservation of mobility of the operated segment. Furthermore, the minimized approach was associated with a less painful postoperative course,⁹⁴ allowing the patients an almost immediate return to unrestricted full activity.

However, Hacker and Miller ⁹⁵ identified 30% of their 23 patients who had failed anterior cervical foraminotomy, requiring at least one additional procedure because of persistence and recurrence of symptoms. With this reoperation rate, which is considerably higher than that of the most series of anterior cervical surgery for radiculopathy, they do not recommend this technique as stand-alone procedure.

Eight years earlier, Brigham and Tsahakis ⁹⁶ presented their experience in 43 patients with radiculopathy due to spondylosis or lateral herniated soft discs treated with anterior foraminotomy and fusion with autogenous bone graft. In this series, 91% of the patients had excellent or good results; however, the fusion rate was 93%, implying loss of motion and risk of increased stress on adjacent segments.

Only one publication dealing with endoscopic anterior cervical foraminotomy has been available until now.⁹⁷ After the practicability of the technique was determined on cadavers, a clinical study of 16 patients was conducted. After a mean follow-up of 13.8 months, the overall subjective patient satisfaction rate was 87.6%, and no major surgery-related complications were encountered. The authors concluded, as in an increasing number of publications focusing on less invasive techniques to decompress the nerve root, that one advantage of the endoscopic technique is the preservation of the intervertebral disc and the motion segment.

Cervical Arthroplasty

After anterior cervical fusion, significant increases in intradiscal pressure and segmental motion at levels adjacent to the fusion have been reported in cadaveric ^98,⁹⁹ and clinical studies.¹⁰⁰^–¹⁰² By definition, adjacent segment degeneration is radiographic changes of degeneration at levels adjacent to a spinal fusion, and ASD means development of new symptoms correlating with adjacent segment degeneration¹⁰³ (Fig. 151-7).

FIGURE 151-7 Sagittal CT scans (left) 10 years after ACDF C5-C6 with PMMA interposition and adjacent level herniated disc at C4-C5. Postoperative plain radiograph after arthroplasty at C4-C5

(Prodisc-C, Synthes).

Hilibrand et al. reported in their study in 1999 a relatively constant incidence of ASD of 2.9% per year,¹⁰⁰ which means that within 10 years more than one fourth of all patients after an anterior cervical arthrodesis may be affected. Ishihara et al. saw an incidence of 19% of their 112 patients followed for 2 years after ACDF.¹⁰¹ However, in 2004, Hilibrand and Robbins¹⁰³ challenged this theory and postulated that there appears to be an incidence of adjacent segment degeneration and disease after arthrodesis that may be related to natural degeneration. Recently, a cadaveric study¹⁰⁴ and a clinical study¹⁰⁵ demonstrated this theory.

Against this background, the use of artificial cervical discs was introduced.¹⁰⁶ The underlying rationale of cervical arthroplasty (CA) is to decompress the neural structures and to maintain physiologic segmental cervical motion after ACD (Fig. 151-8). Through this, adjacent-level motion is decreased, and the incidence of ASD should be eliminated or reduced.⁴⁹ There is no need for graft; the anatomic disc space height is maintained, as is the normal segmental lordosis; and the need for bracing is precluded.

FIGURE 151-8 Plain lateral radiographs demonstrating (A) flexion and (B) extension after arthroplasty at C5-C6 (Prodisc-C, Synthes). (C) Lateral radiograph of artificial disc at C6-C7

(Discover, DePuy).

Recently, many clinical studies ¹⁰⁷^–¹¹⁰ have focused on experience with, and outcome and complications of, one individual with various CA devices. The results are consistently promising, and new devices are increasingly surging onto the market. But with every new technology, issues have to be learned and new problems arise. Issues that might be new for neurosurgeons relate to nomenclature,¹¹¹ materials, and alloys—and therewith topics like wear, toxicity,¹¹¹ biocompatibility,^112,¹¹³ and device-specific side effects.¹¹⁴ Sekhon et al. demonstrated impressively that postoperative visualization of neural structures and adjacent levels after CA is variable among currently available devices.¹¹⁵

Heterotopic ossification or fusion around cervical artificial discs, another challenge for CA, has been reported initially in case descriptions.^116,¹¹⁷ In a multicenter, prospective clinical trial, 17.8% of the studied patients experienced some degree of heterotopic ossification after 12 months,¹¹⁸ and in a recent study two thirds of the patients had such ossification with the same follow-up period.¹¹⁹

The current indications and contraindications change with time and depend on a multitude of factors. Mainly, patients younger than 60 years suffering from radiculopathic symptoms due to a median or paramedian soft disc herniation are good candidates. The inclusion and exclusion criteria of the recent randomized, U.S. Food and Drug Administration–approved, investigational device trial ¹²⁰ were more limited. However, Sekhon presented good results without complications¹²¹ in 11 patients with cervical myelopathy, who were treated with anterior decompression and artificial cervical disc replacement.

About 50% of patients considered for ACDF are now suitable for CA instead. Considering all patients worldwide, this is more attractive for the industry than operation techniques in which no foreign material has to be implanted and motility is preserved (e.g., foraminotomy).

Since the problems of the patients are due to nerve root compression, the short-term results after decompression are comparable to those after any surgical procedure. Currently, only one multicenter, prospective, randomized study has compared the long-term results of cervical disc arthroplasty with ACDF in patients treated for symptomatic single-level cervical degenerative disc disease.¹²⁰ To summarize, there was statistically overall success in five parameters of CA versus ACDF. The artificial cervical disc device maintained physiologic segmental motion 24 months after implantation and was associated with improved neurologic success, improved clinical outcomes, and a reduced rate of secondary surgeries compared with ACDF.

Future Trends

As alternatives to operative treatment, which is invasive and bears a risk of complications, there are regenerative treatment strategies in spinal surgery,¹²² representing therapy approaches in the field of gene technology on a molecular–biologic level.^123,¹²⁴ The starting point is the reduction of aggrecan, a proteoglycan in the cervical disc, which is responsible for the water content and therewith for the volume and the elasticity of the cervical disc.¹²³ In animal models, therapeutic genes (the human transforming growth factor beta 1 encoding gene) were transferred successfully in vivo by means of vectors (adeno- or retrovirus) in target cells inside the cervical disc. The proteoglycan synthesis was thereby stimulated, and the degeneration process was stopped. The results are promising¹²⁴ but far from being a potential approach in humans. Other than the treatment methods described in this review, these future trends could be applied prophylactically, that is, before degenerative alterations become manifest.

Intervertebral disc transplantation ¹²⁵ is another approach with present attempts not only in primates but already in humans. Five years after transplanting fresh–frozen disc allografts in five patients, the neurologic symptoms of all patients improved, and no immunoreaction was encountered.¹²⁵ Despite signs of mild disc degeneration, the motion and stability of the spinal unit was preserved.¹²⁶