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 Table of Contents  
Year : 2019  |  Volume : 2  |  Issue : 1  |  Page : 33-41

Anterior surgical options for cervical spondylotic myelopathy

1 Division of Neurosurgery, State University of Campinas, Campinas, SP, Brazil
2 Department of Orthopedics, Columbia University, New York, New York, USA

Date of Web Publication11-Jan-2019

Correspondence Address:
Dr. Andrei Fernandes Joaquim
Division of Neurosurgery, State University of Campinas, Campinas, SP
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/isj.isj_39_18

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Cervical spondylotic myelopathy (CSM) is one of the most common among causes of spinal cord dysfunction worldwide. In this article, we provide a broad narrative review of the options to treat CSM from an anterior approach to the cervical spine. Anterior procedures are effective and safe, especially for one or two level disease (although can be used up to 7-8 levels). This approach can be used in patients with lordotic, neutral, or kyphotic cervical spine alignment and provide excellent access for direct neural decompression. The most common adverse effects of anterior cervical operations are dysphagia and dysphonia, but fortunately, these are mild and transient in the majority of cases. Severe complications, such as vertebral arterial injury, spinal cord injury or airway compromise, are rare but must be taken into consideration, especially when additional risk factors are present (multilevel procedures, revision surgeries, older, and infirm patients). The primary anterior cervical procedures for treating CSM are anterior cervical discectomy and fusion (ACDF), anterior cervical corpectomy and fusion (ACCF), oblique cervical corpectomy, and cervical disc arthroplasty. A combination (hybrid) of ACDF and ACCF is also utilized as an option to allow for wide decompression, deformity correction, and provide more surface area of exposed, and bleeding cancellous bone. More recently, the senior author (KDR) has utilized a hemi-corpectomy and fusion hybrid technique which will be described in this text. Advantages and disadvantages of each of these options are discussed in detail, as well as the need for posterior instrumentation supplementation in selected patients; such as those with concomitant cervical deformity, poor bone quality, or those at risk for pseudarthrosis following multilevel arthrodeses. The management of patients with cervical spinal cord compression without myelopathy or with mild symptoms is also discussed.

Keywords: Anterior cervical approaches, anterior surgery, arthroplasty, corpectomy, discectomy, spondylotic cervical myelopathy

How to cite this article:
Joaquim AF, Sielatycki JA, Riew K D. Anterior surgical options for cervical spondylotic myelopathy. Indian Spine J 2019;2:33-41

How to cite this URL:
Joaquim AF, Sielatycki JA, Riew K D. Anterior surgical options for cervical spondylotic myelopathy. Indian Spine J [serial online] 2019 [cited 2022 Jul 4];2:33-41. Available from: https://www.isjonline.com/text.asp?2019/2/1/33/249896

  Introduction Top

Degenerative cervical myelopathy (DCM) is the most common cause of spinal cord dysfunction in older adult patients.[1],[2] It represents a multitude of clinical and radiological manifestations of the aging cervical spine such as facet joint arthritis, disc degeneration, uncinated hypertrophy, ligament hypertrophy, spine deformity, and even instability.[1],[2],[3],[4],[5],[6] These degenerative changes can lead to spinal cord compression and clinical signs and symptoms of myelopathy.

In the setting of moderate or severe myelopathy, surgical intervention is widely regarded as the primary treatment option.[2],[3],[4],[5] For mild cases, optimal treatment depends on other factors, such as patient age, electrophysiological and radiological findings, comorbidities, expectations, and surgeons' experience, among others.

The primary goal of surgical treatment is decompression of the spinal cord and clinically affected nerve roots. In some cases, stabilization and spinal realignment may also be necessary to improve clinical outcomes, which is achieved by way of bone grafting and fusion.[2],[4] As an alternative to fusion, motion preservation techniques (such as cervical arthroplasty or laminoplasty) are also used to maintain cervical range of motion and potentially protect the adjacent levels from premature degeneration.

  Patient Selection Top

When surgery is indicated, the cervical spine may be addressed by either an anterior, posterior, or combined surgical approach. There is often much discussion over whether anterior or posterior approaches are superior. Truthfully, the best approach often depends on the individual pathology, surgeon preference and experience, and cervical alignment. In some cases, there is a clear benefit of one approach over the other– for example an anterior approach for focal kyphosis with significant anterior cord compression. In other cases, however, there is true equipoise between either anterior or posterior-based operations, and in such cases, it is likely that a well-performed operation from either side will achieve similar long-term results for the patient. To select the best surgical approach, the expert surgeon should consider the following.

Cervical spine alignment

Normal cervical lordosis (Cobb angle measured from C2 to C7) may range from 20° to 35°.[7] Although some asymptomatic patients may have a kyphotic alignment, posterior cervical uninstrumented approaches such as laminectomies or laminoplasties should generally be avoided in the kyphotic cervical spine (>13–15° of kyphosis). This is because a posterior-based decompression without an instrumented arthrodesis is associated with unfavorable outcomes when there is significant kyphosis.[8] This is particularly true in cases of acute, angular, or focal kyphosis where the spinal cord is draped ventrally over disc/osteophyte complexes or the vertebral bodies themselves. The primary reason for this is that with a kyphotic spine, the spinal cord remains draped across the anterior pathology and does not “float away” from ventral compression even with a wide posterior decompression. When the cervical spine is straight to lordotic, posterior decompression allows for the posterior drift of the spinal cord and thus may result in indirect ventral decompression. The C2–C7 sagittal vertical axis (the deviation of the C2 plumb line from the centroid of the axis to the posterior/superior endplate of C7, SVA) and T1 slope (the angle between the horizontal line and the upper endplate of T1) are also utilized to determine whether a posterior approach is adequate. In the setting of a C2–C7 Sagittal Vertical Alignment (SVA) greater than 4 cm, for example, a non-fusion posterior laminoplasty may lead to worsening sagittal balance.[9]

Number of levels that require decompression

Anterior approaches may feasibly be utilized for decompression/fusion of up to seven or even eight cervical levels. However, adverse effects of the procedure especially dysphagia and pseudoarthrosis increase significantly when multiple levels are treated. Particularly, with long fusions, there is a high chance of pseudoarthrosis at the more caudal levels, thus it could be said that “all anterior” approaches are ideally performed in decompression/fusion of one to three levels.[1],[2],[10],[11]

Other considerations

There are a number of other considerations when selecting the optimal cervical approach. Situations that may favor a posterior over an anterior approach include previous anterior surgery in the cervical spine, head or neck, severe ossification of the posterior longitudinal ligament (OPLL), congenital cervical stenosis of multiple or all cervical levels, site of spinal cord compression, and surgeon's preference and experience. Of these, the surgeon's preference and experience are probably the most important factors. Conversely, an anterior approach may be favored in the setting of focal kyphosis, significant anterior neuroforaminal compression, and large disc herniations compressing the ventral spinal cord, or short-segment disease with only one or two levels requiring decompression. These key factors, among others, all must be factored into the decision of whether to approach the cervical spine anteriorly, posteriorly, or with a combined approach.[10],[11],[12]

The anterior approach has the advantages of allowing for direct spinal cord and nerve root decompression (compared with what is most commonly an indirect decompression for posterior procedures).[1],[2],[10],[11] In a systematic review, Lawrence et al. reported that both anterior and posterior approaches are effective and safe for treating multilevel cervical spondylotic myelopathy (CSM). While anterior approaches are reported to have lower infection rates they have higher dysphagia rates compared with posterior surgery, with similar C5 palsy rates in their review of eight level III studies.[12] Ultimately, an individually tailored strategy should be used to address specific cervical pathologies, primary patient complaints, the patient's goals for surgery, and the feasibility of achieving said goals, considering the experience and resources of the treating surgeon.

In [Table 1] we present a summary of the relationship between the cervical spine characteristics and cervical approaches.
Table 1: Summary of the relationship between the cervical spine characteristics and cervical approaches

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  Complications Top

Fortunately, severe adverse events are relatively uncommon after anterior cervical procedures, however when they occur, they can be catastrophic. The profile of complications depends on the extent of the procedure and also the patient's clinical condition. For didactic purposes, we can divide the complications of anterior cervical surgery according to the period of time that they typically occur.[13],[14]

Intraoperative adverse effects

The most severe adverse effects may occur intraoperatively, although these are rare in experienced hands. Esophageal perforation can occur secondary to retractor placement or direct trauma especially by sharp instruments. Although life-threatening (due to severe infection and airway compromise), this complication is rare, ranging from 0.2% to 0.4%.[15],[16] Immediate recognition and a consultation with an ENT surgeon is mandatory to avoid a missed injury and its consequences. If an injury is suspected, direct inspection of the esophageal wall is recommended before wound closure. It should also be noted that esophageal perforations can present days, weeks and even months postoperatively and can even occur years later due to esophageal erosion against prominent instrumentation or screw.

Neural tissue injury, especially at the spinal cord, occurs in <1% of cases in a large case series. Patients with severe myelopathy, fractures, multiple levels, and a kyphotic cervical spine were at higher risk for spinal cord injury.[13] Intraoperative neurophysiological monitoring may be used to diagnose intraoperative neural injury. In some circumstances, such as in a kyphotic segment distraction, neurophysiological monitoring may allow surgeons to avoid excessive distraction or excessive corrective maneuvers that are not tolerated by the spinal cord.

Other uncommon, but potentially fatal, complications are vertebral artery and carotid artery injury, which require prompt hemostasis and vascular consultation.[10] When feasible and with a nonredundant artery, repair of the injured artery is the best treatment modality, although it may not be possible in all cases. In most instances with a vertebral artery, one can ligate the injured artery, especially if it is a nondominant one. We examine the preoperative magnetic resonance imaging (MRI) on every case we do to determine whether it is in a normal or anomalous position and to ascertain which side has a larger (presumably dominant) artery. Importantly, the treating surgeon must have a premeditated plan in mind in the event of vertebral or carotid artery injury. Swift and effective action on behalf of the surgeon will certainly be the difference between life and death for the patient in such cases. If a major arterial injury occurs, the surgeon must remain calm and first obtain hemostasis using direct pressure. The injured vessel may then be carefully explored and either repaired or ligated; emergent vascular surgery consultation is recommended.

If the vertebral artery has been injured, apply direct lateral pressure until hemostasis is achieved. If that does not work, stuff a small paddy in the foramen transversarium above and below the injury. If the artery is anterior to the foramen distally, compress the longus colli muscle, as the artery lies beneath the muscle. Once the bleeding has been controlled, the artery has to be mobilized. If it is anterior to the foramen transversarium, one will find it under the longus muscle. If it is in the foramen transversarium, one can unroof the costal process (anterior roof of the foramen transversarium) using a sharp curette or a 2 mm Kerrison rongeur.

Dural tears may also occur in anterior decompressions, especially in patients with OPLL. Direct dural repair may not be feasible in all cases and often requires patching with muscle, synthetic materials, or connective tissue. Often, placing one collagen dural sponge under the edges of the remaining dura and another over the tear, followed by placement of a graft directly in front the sponge will tamponade the leak and allow it to heal. In addition, maintaining the head of the bed at 30°–60° postoperatively can decrease the hydrostatic pressure at the site of a cerebrospinal fluid (CSF) leak in the cervical spine and promote healing; a lumbar CSF drain may also be used for this purpose.

Early postoperative period

One of the most severe postoperative complications just after surgery is airway compromise. Most typically, this occurs secondary to cervical hematoma, airway edema, or a combination of the two. Hematomas are best avoided by careful hemostasis especially of the vessels anterior to the longus colli that perforate into the bone at the medial edge of the muscle. We carefully inspect this area prior to closure and wrap these edges with Surgicel (Johnson and Johnson). In addition, we use a ¼” Penrose drain, as we have found that no closed suction drain is immune to clotting whereas the Penrose drain will not clot and will not allow pressure buildup in the retropharyngeal space and thereby prevents airway compromise. Up to 6% of anterior cervical patients may have some degree of airway compromise after anterior cervical surgery.[17] It can be caused by CSF leakage, hematoma, hardware displacement, or even prevertebral swelling and may potentially result in hypoxic brain injury or death. Risk factors are multilevel surgery, prolonged operative time, morbid obesity, significant blood loss, and inadequate hemostasis at closure, among others.[13] In cases of airway obstruction, the typical scenario is that the patient will experience marked and worsening dysphagia, “air hunger” in which they cannot catch their breath, coupled with significant worsening anxiety. Patients will have increasing stridor, develop an altered voice that usually sounds higher pitched and nasally and the work of breathing progressively worsens over just a few hours. Thus, patients that are becoming increasingly agitated and experience increasing dysphagia and voice changes after an anterior cervical procedure should be carefully observed for hematoma progression. If it becomes evident that the patient has an expanding hematoma that is compressing the airway, emergent intervention is absolutely necessary. Patients with progressive airway occlusion should be intubated immediately by an expert anesthesiologist. If intubation attempts fail, the surgical incision must be opened up at the bedside, and a blunt finger sweep of the deep space performed to evacuate the hematoma. After this is done, another intubation attempt is made, and if that is still not successful, an emergent crichothyroidotomy must be done to save the patient's life. After successful intubation, the patient should be taken to the O.R. for wound exploration, irrigation, and hemostasis. In already-intubated patients with persistent or recurrent airway compromise, a temporary tracheostomy may be required.[13]

Transient radiculopathy is also reported in some series, with the most common radicular level at C5 (especially for multilevel corpectomy) – similarly to posterior decompression. One proposed mechanism for causing C5 palsy is excessive cord shift posteriorly, with a stretch neurapraxia on the C5 root. This is mechanism is more likely in the setting of a posterior indirect decompression either by laminectomy or laminoplasty and is likely exacerbated by inadequate neuroforaminal decompression for the C4–C5 neuroforamen. Treatment of C5 palsy is generally conservative, as the symptoms are transient and in most of the cases will resolve over several months.[18] However, if a C5 palsy or radiculopathy does occur, it is important to rule out continued nerve or spinal cord compression by CT and/or MRI. If advanced imaging shows nerve root or spinal cord compression and the patient has correlative symptoms, a revision decompression should be performed. One must be careful to distinguish Parsonage–Turner syndrome (idiopathic brachial plexopathy) from a C5 palsy. With the former, a painful prodrome occurs hours, days or weeks postoperatively. As the pain subsides, the patient develops weakness, most commonly of the deltoid muscle; however, other areas can also be affected. If the imaging studies are negative for a compressive lesion that could be causing the pain and neurological deficit, an electromyography can be obtained a few weeks postoperatively to look for a Parsonage–Turner syndrome.

Dysphagia is the most common adverse effect after anterior cervical spine procedures.[19] In prospective studies, up to 71% of the patients had at least some degree of postoperative dysphagia.[20] The etiology of dysphagia is multifactorial; swallowing problems after anterior cervical surgery are attributed to esophageal denervation/manipulation, soft-tissue swelling/edema, prominence of the hardware (such as plates), hematoma, and nerve root injuries. In general, the pharyngeal plexus may be injured in surgeries from C2 to C5, the superior laryngeal nerves from C3 to C4, the recurrent laryngeal nerves between C5 and T1 and the hypoglossal nerve in surgeries above C3.[13] Some mild degree of dysphagia is reported in more than 50% of the patients in prospective studies, and symptoms improved within a few weeks in the majority of the patients. Multilevel surgeries, female sex, older patients (age >60 years-old), revision procedures, and thicker plates are risk factors for dysphagia.[15] In the most severe cases of refractory dysphagia, a feeding tube may be required to maintain nutrition. Local corticosteroid can theoretically decrease postoperative swelling and related dysphagia, especially for patients with high risk for severe dysphagia; although this remains somewhat controversial.[21] Strategies to decrease dysphagia are to reduce operative time (specifically retractor time) by moving efficiently through the case. If self-retaining retractors are used, the surgeon should be mindful of how long the retractor has been in place. It is advisable to relax the retractors as much as possible (when obtaining X-rays or while cutting bone graft); and if retractors are in place for more than 3 h during an anterior procedure, the surgeon should consider keeping the patient intubated overnight to avoid airway occlusion from edema.

Dysphonia is defined as voice change, from mild hoarseness to a severe speaking problem, with an incidence ranging from 2% to 30%.[13] It also has a multifactorial etiology, such as recurrent or superior laryngeal nerve injury, direct vocal cord trauma, arytenoid dislocation and laryngeal edema. The incidence is lower than that of dysphagia, although it is potentially underreported. Symptoms are generally transient, but in cases of persistent dysphonia, specific consultation of a voice specialist is required.

Another early adverse effect that deserves mention is graft or hardware extrusion, which may require a revision procedure and is associated with more extensive procedures (such as multilevel corpectomies or spine reconstructions for deformities).[10] Finally, wound infection may occur, which is extremely uncommon after anterior cervical procedures due to the excellent vascularity and also good lymphatic drainage of the cervical tissues. Checking for esophageal perforation is recommended in the setting of a deep anterior cervical infection. Treatment generally consists of antibiotics and surgical exploration for irrigation and debridement of the surgical wound, graft, and instrumentation.

  Types of Anterior Cervical Approaches Top

Anterior cervical discectomy and fusion

Anterior cervical discectomy [Figure 1] is one of the most common spinal procedures performed around the world, described in 1955 by Smith and Robinson.[22] It provides excellent visualization for ventral spinal cord decompression for disc herniations, as well as foramen decompression and the ability to restore cervical lordosis.[1] Additional benefits associated with anterior cervical discectomy and fusion (ACDF) may also be decreased spondylotic neck pain and prevention of recurrent stenosis at the operative level.
Figure 1: This patient had cervical radiculopathy with multilevel foraminal stenosis. Cervical lateral (a) and anteroposterior (b) plain radiographs. T2 sequence sagittal magnetic resonance imaging without evidence of spinal cord compression (c) but with foraminal stenosis on the left at C4–C5 (d), bilaterally at C5–C6 (E) and C6–C7. He underwent a three-level cervical discectomy and fusion from C4 to C7 with plating (g and h, postoperative plain radiographs – lateral and anteroposterior, respectively)

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Allogeneic bone graft (allograft), autogenous bone graft (autograft), or synthetic cages may be used in the disc space to achieve fusion. Considering the use of a cervical plate, a recent metanalysis reported that locked anterior plate usage may improve fusion rates, decrease subsidence, and provide slightly better visual analog scale (VAS) neck pain scores.[23] Although this metanalysis did not report a higher dysphagia rate with plates, some authors believe that a prominent plate may contribute to postoperative dysphagia.[19] Strategies for minimizing plate-related dysphagia include removing all anterior osteophytes to allow the plate to sit flush on the ventral spine, bending lordosis into the plate to allow it to follow the natural contour of the spine, and using a low-profile plate. Some stand-alone interbody devices with screws may also avoid the need of a plate altogether. However, for patients with cervical spondylolisthesis or dynamic changes on plain radiographs, segmental fixation with plate and screws are recommended, as this has been shown to provide the greatest rigidity and stiffness.[1],[2],[24]

Of note, plate characteristics should be taken into account when performing an anterior cervical fusion. Dynamic cervical plates were designed to allow a better load sharing of the graft while providing resistance to motion. Rigid plates had some low load sharing across the graft, potentially, decreasing the stress that promotes healing – the more rigid the plate, the more load in the plate itself and less in the graft. However, it is speculated that rigid plates had less risk of segmental kyphosis or foraminal narrowing (Rhee and Riew– Dynamic anterior cervical plates). Although dynamic plates were designed with theoretical advantages over rigid plates, there is lack of evidence attesting the superiority of dynamic over rigid plates. Surgeons should use plate design that they were more comfortable and had more experience until further evidence exists.

Anterior cervical corpectomy and fusion

When spinal cord compression is beyond the disc space and extends behind the vertebral body, a cervical corpectomy may be necessary to adequately decompress the spinal cord.[24] Similar to ACDF, different interbody devices may be used, such as titanium mesh cages, allograft, autologous bone (iliac crest, fibula, rib grafts), and PEEK cages, among others. The morbidity of a corpectomy is slight greater than an ACDF, related primarily to more blood loss and longer operative times. There is also potentially a higher chance of pseudoarthrosis if it is not technically performed well. Plating is generally mandatory in anterior cervical corpectomy and fusion (ACCF). Anterior fixation is used to avoid not only pseudoarthrosis but also to prevent graft dislodgement.[25] Long strut grafts used for multilevel corpectomies are mechanically unfavorable and are prone to construct failure.[24] For this reason, posterior supplementation to avoid graft extrusion or hardware failure is advisable when multilevel corpectomies are performed. One alternative to stabilizing long strut grafts is the use of a buttress plate (fixed only in at one end of the construct to avoid graft dislodgement).[26] However, caudal buttress plating has been reported to cause airway obstruction if it dislodges. This is because if the graft extrudes, the plate kicks out at a 45° angle, obstructing the airway and potentially causing asphyxia and death.[27] The risk remains, even when used in conjunction with posterior instrumentation. Although treatment is individualized according to patient's characteristics (radiological, comorbidities, and bone density), for two or more level corpectomies, we recommend both anterior plating and posterior supplementation to minimize graft extrusion. While a two-level corpectomy may be performed as stand-alone procedures in selected cases, great care must be taken to achieve perfect graft press-fit and to avoid edge-loading. Rigid immobilization and frequent radiographic evaluation are recommended. We feel that the safer alternative is to augment the construct with posterior instrumentation and arthrodesis.

In selected cases with two-level disc disease in patients with increased risk for pseudoarthroses, such as heavy smokers or diabetics, a single-level corpectomy may be advantageous compared with a two-level ACDF.[24] The posterior vertebral body (about 2–3 mm) can be left intact to avoid graft retropulsion into the spinal cord, and fusion need only take place at two graft-bone interfaces, as opposed to four interfaces with a two-level ACDF. In addition to fewer graft-bone interfaces, the cancellous bone of the excised vertebral body is rich in osteoprogenitors and can be utilized as autogenous bone graft.

An alternative to multilevel corpectomies is to perform a hybrid procedure with a combination of a corpectomy with an ACDF.[24] The advantage of this method over a traditional multilevel corpectomy with a long strut graft is the ability to put screws into all involved vertebral bodies to achieve segmental fixation, recreate lordosis, and attain a stronger biomechanical construct. For three-level disease, instead of a three-level ACDF, surgeons may choose to perform a one level corpectomy for the cranial two levels and an ACDF at the most caudal level, with a plate across all three levels. We described this technique as being a corpectomy-discectomy.[24] Finally, as an alternative for four-level disease, two single-level corpectomies (corpectomy-corpectomy or skip-corpectomy) separated by an intervening vertebra may be a very reasonable option. Increasing the number of screws in the plate fixation may decrease the long-term risk of hardware fatigue and also improves construct rigidity to promote bone healing.[24]

Hemi cervical corpectomy and fusion

Recently, the senior author (KDR) has proposed the use of a longitudinal hemi-corpectomy and fusion (HCCF), which consists of removal of only half of the vertebral body eccentric to one side longitudinally. In HCCF, a longitudinal corpectomy is performed preferentially to one side, which preserves the vertebral body on the contralateral side. This technique differs from traditional cervical corpectomy in which the corpectomy is performed from uncus to uncus, leaving only the lateral walls of the vertebral body. With HCCF, the preservation of one hemivertebral body thus increases surface area of exposed cancellous bone, allows the surgeon to achieve segmental fixation across the corpectomy site, allows the surgeon to obtain local cancellous autograft, and potentially increases the fusion rates. It is only appropriate in cases where the cord compression can be addressed by decompressing 50%–80% of the width of the vertebra, allowing screw fixation into the remaining body. We also place small bone grafts into the remaining disc spaces of the unremoved vertebral body to enhance stability and fusion rates. The HCCF technique is illustrated in [Figure 2]. In the early experience of the senior author, the HCCF has shown more rapid time to union in three-level decompression/fusion cases in which HCCF is performed above a traditional ACDF for three-level decompressions. This technique may be used as a viable alternative to standard corpectomies, restoring lordosis. Further studies are necessary to evaluate the benefits of this technique over conventional ACCF. [Figure 2], [Figure 3], [Figure 4] illustrates the hemi cervical corpectomy technique.
Figure 2: Anterior cervical hemicorpectomy, discectomy, and fusion. Illustrative picture. Note that this technique is especially useful for three-level disease, and a screw is placed in the remaining hemivertebra, providing additional fixation

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Figure 3: Intraoperative view (a) anterior cervical hemicorpectomy, discectomy, and fusion. (b) The allograft is placed in the hemicorpectomy side after proper decompression

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Figure 4: This patient had cervical radiculopathy with multilevel foraminal stenosis and also some mild spinal cord compression with myelopathy. Cervical lateral (a) and anteroposterior (b) plain radiographs. T2 Sequence Sagittal magnetic resonance imaging with mild spinal cord compression (c) and multilevel foraminal stenosis at C4–C5 (d), C5–C6 (e), and right C6–C7. He underwent a hemicorpectomy at C5 and a discectomy at C6–C7 with plating (g and h, postoperative plain radiographs – lateral and anteroposterior, respectively)

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Cervical arthroplasty

ACDF has for many years been considered the gold standard surgical treatment for focal CSM treated anteriorly. More recently, the theoretical advantage of preserving cervical spine range of motion was postulated to decrease iatrogenic adjacent segment pathology. In this context, many intervertebral disc implants, also known as cervical disc arthroplasty (CDA) devices, were developed to preserve at least some degree of motion at the treated level.[28],[29],[30],[31] The indications for cervical arthroplasty for CSM are those with one or two-levels due to retro-discal cord compression. It is not appropriate for those with retro-vertebral cord compression, which would require a corpectomy. Patients should also have a preserved disc height (at least 3 mm according to some authors), good bone density (no osteoporosis) and preserved motion. Contraindications include instability, inflammatory or metabolic disease, ossifying diseases (e.g., DISH, OPLL, ankylosing spondylitis), segmental kyphosis, and severe facet joint arthritis.[30],[31] Respecting these indications, CDA is associated with excellent clinical results for CSM or cervical radiculopathy.[28],[29]

To be sure, there has been some controversy regarding the superiority of cervical arthroplasty over ACDF for patients with myelopathy, given that one way to treat myelopathy is to immobilize the neck in a brace. However, it has been shown that in properly indicated cases the outcome of myelopathy is quite similar or even slightly superior in several high-quality studies.[22],[28],[29] In addition, many recent studies provide some evidence of multilevel CDA and also hybrid procedures, such as an ACDF in the most degenerated level and a CDA above, in the disc with mild degeneration.[30],[31] Of note, CDA is technically more demanding than ACDF procedures–the disc space preparation and insertion of the implant must be properly sized (generally occupying all the disc space) and perfectly aligned. Surgeons must take great care to avoid coronal imbalance and endplate violation during disc space preparation; otherwise, CDA may result in heterotopic ossification, continued pain, and the need for revision (requiring an ACDF or even ACCF).

Oblique cervical corpectomy

Oblique cervical corpectomy (OCC) is a lateral cervical approach used as an alternative to a central corpectomy, with the advantage of preserving motion since no fusion is performed.[32] It may be used for one or multilevel spinal cord decompression, also allowing unilateral nerve root decompression.[32] The surgical technique is slightly different from a Smith–Robson approach – the head is slightly rotated to the contralateral side of the approach and slightly extended as well. The incision is also in the anterior border of the sternocleidomastoid muscle, but the plane is lateral to the neurovascular tract (jugular vein and carotid artery).[32] The longus colli muscle is retracted medially, contrary to the standard Smith–Robinson approach, increasing the risk of vertebral artery and accessory nerve injury, as well as postoperative Horner's syndrome.[32] Then, in the area of intersection of the vertebral body and the transverse process, a vertical drilling is starting in the direction of the vertebral body. After reaching the posterior longitudinal ligament (PLL), further drilling is continued obliquely to the contralateral side, until the end of the PLL.

Cadaveric studies suggested that multilevel oblique corpectomy without graft had less instability than a standard corpectomy with graft but without a plate.[33] Of note, it results in increasing motion (15% in flexion, 18% in extension, 11% during lateral bending and 18% during axial rotation) compared with a normal cervical spine.

A large clinical study of 499 patients who underwent OCC was reported by Chibbaro et al.[34] A total of 900 levels were decompressed, most of them at C 4-5 (21% and C 5-6 (33%). A high level of neurologic recovery was report (up to 80%), and only three patients require further surgery due to instability.

Although effective, probably OCC did not become popular due to be technically demanding and also with a high risk of vertebral artery injury and Horner's Syndrome.[32]

  Management of Patient With Cord Compression but No Evidence of Myelopathy or Mild Cervical Myelopathy Top

As many patients may have access to a cervical MRI due to acute and transient neck symptoms, such as focal and acute pain, most surgeons will encounter a common clinical scenario spinal cord compression on imaging but without clinical signs or symptoms of myelopathy.

This situation is somewhat complicated: the risk of paralysis on a yearly basis is about 1–2 in 30,000 for the general population. Even if the risk of a patient with cord compression is 10 times greater than an average person's, it is still just 1–2 in 3000, which is similar to or lower than the risk of a catastrophic event during spine surgery in experienced hands. Surgery in this situation is an option; however, the patient should be made aware of the risks and benefits of both surgical and nonsurgical treatment. In a recent consensus statement regarding the treatment of myelopathy, AO spine published clinical practice guidelines for the treatment of myelopathy. In these guidelines, constructed by a panel of the world's experts in cervical spine care, it is recommended that patients in this category be told of their increased risk for developing myelopathy. In this setting, surgery may be considered, however, it is also reasonable to closely follow the patient with serial clinical examinations. If the patient develops myelopathic signs and symptoms, at that time surgery is generally recommended.[35]

Bednarik et al. have followed 199 patients with cervical spinal cord compression without clinical signs of myelopathy for at least 2 years (range 2–12 years of follow-up).[36] They reported that clinical evidence of first signs and symptoms was found in 45 patients (22.6%), with symptomatic CSM developing in 12 months in 16 patients (35.5%). On multivariable analysis, they reported that electrophysiological abnormalities of cervical spinal cord dysfunction, clinical radiculopathy and T2 MRI hyperintensity signal change were useful predictors of early progression to myelopathy. Of note, the majority of patients were asymptomatic during the study follow-up, suggesting that nonoperative management is a good option, especially for those without risk factors for CSM. In addition, Bednarik's data suggests that those with evidence of spinal cord compression and clinical radiculopathy are at high risk of progressing to myelopathy, and in such cases, the surgeon should consider offering surgical decompression as the first line of treatment.

In conclusion, close clinical follow-up is recommended for asymptomatic patients with spinal cord compression. Testing walking ability and gait coordination, hand coordination, and fine motor skills frequently are recommended. In the setting of risk factors for progression, such as cervical radiculopathy, electrophysiological dysfunction or MRI signal changes, earlier surgical treatment, may be considered.

  Outcome Following Operative Treatment for Cervical Spondylotic Myelopathy Top

In a systematic review and meta-analysis, Fehlings et al. evaluated the changes in impairment, disability, and pain following operative treatment for CSM.[37] A total of 32 articles were evaluated, assessing functional status, disability, pain and also complication. Pooled standard mean differences showed a large effect for improvement in myelopathy severity scales (Japanese Orthopaedic Association and modified Japanese Orthopaedic Association) from baseline at all times of follow-up (short, medium, and long-term). They also reported improvements with statistical significance in Nurick, Neck Disability Index and VASs sores with a low incidence of complications (14.1%; 95% confidence interval [CI] = 10.1% to 18.2%). They concluded that surgical treatment improves significantly pain, disability, and function in CSM patients, with a low rate of adverse effects. Patients with shorter duration of symptoms and less severe myelopathy before surgery had higher rates of a postoperative mJOA ≥16 (the maximum value is 18 and reflects normal neurological function).

  Conclusion Top

Overall, there are a number of good surgical options for treating patients with cervical myelopathy. The anterior cervical approach allows for direct neural decompression, restoration of sagittal alignment, and avoids significant muscle dissection. As we have described, there are also a number of reconstruction options after anterior decompression including ACDF, ACCF, hemicorpectomy, hybrid fusions, and CDA. These operations offer some significant advantages over posterior-based operations in properly selected patients with amenable pathology. Likewise, there are some disadvantages to anterior approaches, namely complications of dysphagia, hematoma with airway occlusion, and pseudarthrosis. The expert spine surgeon should be aware of these advantages and risks, as well as be aware of the goals of the operation and the limitations of the proposed approach. The best approach for any given patient may vary greatly depending on the patient's and surgeon's goals of the procedure, as well as the specific pathology being addressed. An informed discussion between the surgeon and patient is recommended, as the best surgical approach will depend not only on the technical considerations but also on the patient's goals and expectations for surgery.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]

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