Eur Spine J DOI 10.1007/s00586-015-3784-6
ORIGINAL ARTICLE
Anterior approaches for cervical spondylotic myelopathy: Which? When? How? Sanford E. Emery
Received: 30 November 2012 / Revised: 27 January 2015 / Accepted: 27 January 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract Cervical spondylotic myelopathy is a degenerative disorder with an unfavorable natural history. Surgical treatment options have evolved substantially over time, with both anterior and posterior methods proving successful for certain patients with specific characteristics. Anterior decompression of the spinal canal plus fusion techniques for stabilization has several advantages and some disadvantages when compared to posterior options. Understanding the pros and cons of the approaches and techniques is critical for the surgeon to select the best operative treatment strategy for any given patient to achieve the best outcome. Multiple decision-making factors are involved, such as sagittal alignment, number of levels, shape of the pathoanatomy, age and comorbidities, instability, and pre-operative pain levels. Any or all of these factors may be relevant for a given patient, and to varying degrees of importance. Choice of operative approach will therefore be dependent on patient presentation, risks of that approach for a given patient, and to some degree surgeon experience. Keywords Cervical myelopathy Anterior approach cervical spine Anterior cervical discectomy and fusion Anterior cervical corpectomy and fusion
Introduction The operative treatment of cervical spondylotic myelopathy has evolved over several decades, and today there is S. E. Emery (&) Department of Orthopaedics, West Virginia University, PO Box 9196, Morgantown, WV 26506-9196, USA e-mail: [email protected]
often more than one option for obtaining successful outcomes in this patient population. After clarification of the clinical entity of cervical myelopathy, largely in the literature of the 1950s from pathoanatomic studies, the posterior approach with multi-level laminectomies was initially utilized. The anterior approach became more widely accepted in the 1970s and 1980s, probably due to better characterization of the pathoanatomy of cord compression offered by CT myelography and later by magnetic resonance imaging. Beginning in Japan in the late 1970s and 1980s, laminoplasty was developed as an operative method followed by laminectomy and fusion when improved posterior cervical instrumentation became available.
Methods The review of the literature was undertaken using the PubMed.gov vehicle. The keywords entered into the search were ‘‘cervical myelopathy’’ AND ‘‘anterior surgery’’. This yielded 1,635 abstracts in the English language which were reviewed by the author. The search timeframe was from 1963 to 2013. Sixty-five articles were chosen by the author and reviewed for their relevance regarding the anterior versus posterior approach for cervical spondylotic myelopathy and anterior reconstructive techniques in the cervical spine. Advantages of the anterior approach for cervical spondylotic myelopathy The anterior approach to the spine using a standard Smith– Robinson technique is quite safe and straightforward for the trained spine surgeon. Potential complications will be
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discussed below, but serious complications are quite uncommon. The main advantages of the anterior operative approach for this disorder include: Direct removal of the compressive pathology In the vast majority of cases, compression of the cervical cord producing myelopathy stems from anterior pathology such as disc herniations, osteophytic changes, kyphosis, and subluxation. The anterior approach allows for removal of the compression, either with a simple discectomy or larger decompression techniques such as hemicorpectomy, corpectomy, or multi-level corpectomies. Foraminotomies can be successfully performed from an anterior approach as well by decompressing or totally removing the uncovertebral joint areas. With direct removal of the pathology, one might expect better neurologic recovery. This topic has been studied with conflicting results. In many scientific articles, the neurologic outcome for myelopathy with or without radiculopathy has at least been as good as posterior procedures or, in some studies, slightly better [1–5]. In one 10-year follow-up study of corpectomies versus laminoplasty, neurologic outcome remained equivalent in both groups [6]. Cunningham et al. [7] in a review of 11 cohort studies also found similar neurologic outcomes for anterior versus posterior groups. However, Hirai et al. [1] looked at their experience with anterior versus posterior cohorts and found better neurologic recovery in the anterior group, particularly with respect to upper extremity function. Less recovery in the posterior group was believed to be due to residual anterior cord compression. Mummaneni et al. [8] in a thorough literature review, noted similar neurologic outcomes for the two approaches in spondylotic myelopathy patients, with the exception of late deterioration evident in the laminectomy alone outcomes. A recent meta-analysis of ten articles focused on anterior versus posterior approaches for treatment of myelopathy suggested neurologic recovery was equivalent if the occupying ratio of canal compromise was \60 % [9]. Of note is that this review included studies of OPLL, and reportedly included few if any laminectomy plus fusion patients. Another metaanalysis of eight studies for spondylotic myelopathy patients did include anterior, laminoplasty, and laminectomy plus fusion groups [10]. These authors found better neural recovery with anterior decompression and arthrodesis at the cost of a higher complication rate. Fehlings et al. [11] recently published the outcomes of the prospective, multi-center study of cervical spondylotic myelopathy patients from the AOSpine consortium comparing anterior vs. posterior approaches. One hundred sixty-nine patients underwent anterior surgery and 95 posterior surgery (mostly laminectomy and fusion).
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Multiple validated outcome measures were utilized. Though the choice of technique depended on surgeon preference, multivariate analysis methods were used to control for baseline confounders. The results demonstrated that anterior and posterior approaches had equivalent beneficial outcomes in the treatment of cervical spondylotic myelopathy. Complication rates were also equivalent, with the exception being a trend toward a higher infection rate in posterior surgeries. Correction of deformity Anterior discectomies or corpectomies with bone graft or cage reconstruction will allow for correction of cervical kyphosis, which is by far the most common deformity seen in this patient population. Uchida et al. [12] compared patients with pre-operative kyphosis [10° who underwent either anterior corpectomy or laminoplasty procedures for spondylotic myelopathy. Average kyphosis decreased 46 % in the anterior group and 15 % in the laminoplasty group. Discectomies with interbody fusion have been shown to statistically correct kyphosis better than corpectomy and strut graft procedures (post-operative lordosis of 17.6 vs. 14.5 degrees, respectively) [13]. Along with neural decompression, achieving satisfactory sagittal balance is a tenet of surgical treatment for cervical myelopathy [14]. Flexible kyphotic deformities may be amenable to posterior decompressions with an instrumented fusion holding them back in an acceptable position, but more rigid kyphotic deformities will typically require at least an anterior approach and, at times, a circumferential strategy [15]. Arthrodesis Fusion of the cervical spine can, of course, be a doubleedged sword with potential future complications of adjacent segment degeneration. Hilibrand et al. in a retrospective review of 374 patients calculated a 2.9 % incidence per year of symptomatic adjacent segment disease in patients with prior cervical arthrodesis. At 10 years, the prevalence was 25 % [16]. Nunley et al. looked at radiographic adjacent segment changes in 170 patients in both an anterior fusion group and disc arthroplasty group of a randomized study. At a median follow-up of 42 months (range 28–54 months), adjacent radiographic changes occurred in 14.3 % of the fusion group and 16.8 % of the arthroplasty group [17]. Though not without potential downstream side effects, arthrodesis remains a critical strategy for patients with instability or cervical kyphosis. Anterior arthrodesis techniques may have the potential benefit of distraction with indirect opening of the foramen compared to posterior fusion techniques. Either approach, having obtained a successful fusion, will provide good
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relief of axial neck pain in most patients [3]. Wada et al. [6] documented only 15 % of patients with neck pain 10 years after anterior corpectomy and arthrodesis for myelopathy vs. 40 % in a laminoplasty group. Ghogawala et al.[18] documented improvement in the Neck Disability Index, a validated questionnaire measuring neck pain, for both posterior fusion and anterior fusion groups in his comparative study on myelopathy patients, with the best results vs. baseline symptoms in the anterior group. Though both groups were posterior approach techniques, Hightower et al. [19] noted no improvement in pre-operative visual analog (VAS) pain scores for a laminoplasty group but statistically significant improvement in VAS scores in a posterior laminectomy and fusion group, suggesting arthrodesis can help neck pain. Disadvantages of the anterior approach for cervical spondylotic myelopathy There are certain downsides of the anterior operative approach compared to posterior options: Higher complication rates Multi-level anterior procedures are more technically demanding than posterior options. Two- or three-level anterior corpectomy procedures will typically take longer and encounter more blood loss than, for example, a multilevel laminoplasty procedure [6]. Several studies have noted an increased rate of complications for anterior patients. Edwards et al. [20] in a small study of matched cohorts found more complications including nonunion, persistent dysphagia and dysphonia, and adjacent segment problems in the multi-level corpectomy group. Fehlings et al. [21] in a multi-center prospective study of spondylotic myelopathy patients found the risk of peri-operative complications to be related to age, combined anterior–posterior procedures, increased operative time, and blood loss but not anterior versus posterior approaches alone. Hirai et al. [1] documented more complications in their anterior cohort group, including airway issues, dysphagia, and pseudarthrosis versus the laminoplasty group. Three systematic reviews of cohort studies also concluded that post-operative complications are greater for multi-level anterior surgical approaches compared to posterior options [7, 9, 10]. Interestingly, the well-studied but not well understood C5 root palsy complication can occur after either anterior or posterior treatment of cervical myelopathy. Historically, studies documented the incidence anywhere from 4 to 16 % in laminoplasty patients, and it was initially associated with that specific procedure. More recently, however, studies have noted similar rates in anterior corpectomy patients [22] or equivalent rates in cohort studies [1].
Strut graft/interbody reconstruction Meticulous technique (i.e., good carpentry!) is very important for the stability and healing potential of anterior strut graft reconstruction. Migration or dislodgement of long struts is enough of a risk that many surgeons utilize a circumferential procedure for three or more level corpectomy patients [23, 24], and even some two-level corpectomy patients with kyphosis or severe osteoporosis. Longer term risks of pseudarthrosis can be significant for multilevel anterior cervical discectomy and fusion (ACDF) procedures even with anterior plating [25, 26]. Dysphagia and airway issues Though airway complications can occur at any time, they are more problematic in long anterior corpectomy and reconstruction procedures [27]. In recent years, dysphagia has been documented to be more common than previously thought for the anterior approach. The vast majority of swallowing symptoms resolve relatively quickly, but can be persistent for years in a small percentage of patients [28–30]. Bazaz et al. [28] documented some degree of dysphagia 6 months following anterior cervical arthrodesis in 208 patients, with mild difficulty reported by 17.8 % of patients, moderate by 4.3 %, and severe by one patient. Loss of motion and post-operative bracing Many discectomy and fusion patients and all multi-level corpectomy patients require some form of post-operative bracing to help maintain stability in the early post-operative period and encourage successful arthrodesis. Bracing is used by many surgeons to help maintain stability in the early post-operative period and encourage a successful arthrodesis. High-quality studies that would offer evidence-based guidelines regarding the need for a brace, type or duration of bracing after anterior procedures is lacking. Of course, arthrodesis is designed to immobilize the operative segments of the spine and will inherently decrease range of motion, depending on the number of levels fused. Though earlier studies demonstrated substantial loss of mobility after laminoplasty [6], more recent attention to early range of motion post-operatively and less bracing has minimized loss of motion after laminoplasty [31]. Decision-making considerations Given the relative advantages and disadvantages of the anterior approach for cervical spondylotic myelopathy, for any given patient the surgeon should consider the following factors:
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Sagittal alignment of the cervical spine As mentioned, a flexible deformity may be successfully treated with posterior decompression and stabilization in a satisfactory position but, generally speaking, cervical kyphosis, particularly fixed kyphosis, warrants anterior decompression and stabilization techniques. Uchida et al. [12] noted less neurologic improvement in patients with 10° or more of kyphosis if treated with laminoplasty. Pathoanatomy Though the paper concerned OPLL patients, Iwasaki et al. [32] showed that hill-shaped lesions responded better to anterior decompression, and more flat type of compression did well with laminoplasty. In that study, if the compression ratio was [60 %, patients had better neurologic recovery with anterior decompression than laminoplasty. If we extrapolate this finding to spondylotic myelopathy patients, then disc protrusions or osteophytes that jut into the spinal cord causing a kidney bean type of anterior deformation are perhaps best treated with an anterior technique in order to adequately decompress the cord. More of a generalized stenosis where there is flattening of the anterior cord may be amenable to either posterior or anterior decompression procedures [32]. Though not as common as anterior cord compression, infolding of the ligamentum flavum with posterior canal compromise may warrant a posterior approach for any given patient. Intra-parenchymal signal change of the spinal cord in the setting of cervical myelopathy is believed to result from chronic compression causing myelomalacia. A recent study by Arvin et al. [33] looked at 57 patients prospectively and concluded that MRI signal changes, such as increased T2 signal and low T1 signal, were predictors of initial neurological status and post-operative recovery. In a systematic review of the literature, Karpova et al. [34] investigated the value of signal change and other factors on predicting surgical outcomes. The authors also concluded that signal changes could help predict surgical outcomes in spondylotic myelopathy. Although these studies and others suggest that signal change may be important for surgical indications and post-operative recovery, there is no data in the literature to suggest anterior approaches are better or worse than posterior approaches for the operative treatment of myelopathy in this subpopulation of patients. Number of levels involved In Fraser’s meta-analysis, for three levels of pathology, anterior cervical discectomy and interbody techniques will have a lower rate of successful arthrodesis than one- or
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two-level interbody procedures and lower than corpectomy procedures [35]. Multi-level corpectomies with strut reconstruction are more demanding for the surgeon and the patient and may require circumferential stabilization. For a given patient with myelopathy with other factors being equivalent, the number of operative levels is often the deciding factor for choice of operative approach. Subluxation or instability If degenerative changes have led to subluxation of specific segments or certainly with dynamic instability, arthrodesis is indicated. Instability requiring operative stabilization may be difficult to define in the spondylotic patient with myelopathy, which is a different population than those with acute trauma. Generally, 2 mm of translational motion is acceptable in these patients and 4 mm may warrant surgery, though other factors such as the size of their spinal canal, pain symptoms, and medical condition are important. No evidence-based literature defines operative indications for a specific amount of motion, to this author’s knowledge. Bone quality Severe osteoporosis can be problematic due to long strut graft settling [36] as well as difficulty achieving stable fixation with anterior plates. This potential complication may tip the scales for posterior laminoplasty procedures if other factors make that a reasonable option. Neck pain Though not well elucidated in the literature to date, the amount of pre-operative neck pain displayed by any given patient does play into the decision of operative approach. By definition, patients with cervical spondylotic myelopathy usually have significant spondylosis and disc degeneration, which often is a main contributor to their cord compression. Though the source of axial neck pain is not totally understood, in a patient with moderate-to-severe neck pain and significant degenerative changes, this author would recommend fusion as part of the operative treatment, rather than just a decompression such as laminoplasty. Liu et al. [9] in their meta-analysis of anterior vs. posterior studies found no differences in axial pain outcomes, but noted that only two of the ten studies reviewed actually reported pain outcomes. Cunningham et al. [7] in their literature review concluded that laminoplasty patients had more post-operative neck pain, but they quoted older studies where bracing, prolonged immobilization, and opening the C7 lamina were standard methods [6, 37].
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Risks and patient factors Knowing the pros and cons of anterior and posterior approaches, the surgeon must consider the particular patient and apply that knowledge to that individual. A patient having had multiple prior anterior approaches or previous recurrent laryngeal nerve palsy is probably a better candidate for a posterior surgical approach. The frail,
elderly patient with chronic obstructive pulmonary disease may steer us away from a multi-level corpectomy and strut graft procedure where airway and swallowing issues could be problematic post-operatively. Patients with severe spondylosis, significant neck pain, and focal disc herniations at one or two levels with frank deformity of the spinal cord are excellent candidates for an anterior approach with a two-level discectomy and fusion. The choice of operative procedure for the treatment of cervical spondylotic myelopathy is partly art and partly science. Some patients are better candidates for either an anterior or a posterior technique, whereas many others can be successfully treated with either approach, as graphically summarized in Fig. 1. A horizontal flow chart is offered (Fig. 2) as an aid for the surgeon to consider the options for any given patient. Though this chart is ‘‘linear’’ in presentation, in reality it is more of a matrix thought process since the decision-making parameters may be weighted differently in an actual clinical situation. Selection of anterior operative techniques
Fig. 1 Diagram illustrating patient selection for anterior versus posterior approaches for surgical treatment of cervical myelopathy. (Reprinted with permission from The Cervical Spine, 5th edition, Benzel et al. eds. Lippincott, Williams and Wilkins, 2012, p. 1012.)
Anterior decompression and fusion procedures can be placed in three categories: (a) discectomy and fusion techniques; (b) corpectomy and strut grafting techniques,
Fig. 2 Flow chart for decision-making in the choice of operative approach and technique. This list of factors the surgeon should consider may be weighted differently for any particular patient, thus a ‘‘blended’’ cost–benefit analysis requires surgeon judgment
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and (c) hybrid procedures. Discectomy and fusion procedures involve removing the disc and any posterior osteophytes in order to obtain decompression of the canal. This procedure is quite adequate for soft disc herniations provided they have not migrated cephalad or caudad behind vertebral bodies. More spondylotic changes of the endplates may require partial corpectomies in order to adequately decompress the spinal canal, using slightly taller strut grafts or cages to provide anterior stabilization and ultimate arthrodesis. If the pathoanatomy of the cord compression is amenable to discectomy and fusion at the necessary levels, then this technique actually gives better correction of cervical kyphosis than does multi-level corpectomy techniques since distraction is over several segments [13]. There is a documented pseudarthrosis rate of 18 % or higher with a three or more level ACDF [25, 26, 35], however, so this needs to be taken into account when considering choice of technique and host factors. Corpectomy and strut graft techniques are ideal for decompressing the spinal canal when there is spinal cord compression behind the vertebral bodies. A corpectomy allows the surgeon to come down directly on the pathoanatomy and safely remove it. At times, when there are large osteophytic changes at the endplates over multiple segments and severe cord compression, this author believes it is safer to perform corpectomies in order to avoid neurologic complications and ensure adequate decompression over several levels than to attempt limited discectomies at each level. Strut grafting over multiple levels does limit the number of surfaces requiring osseous healing, though it is unclear this lowers the nonunion rate compared to multilevel discectomy and interbody grafting. Hilibrand et al. [38] documented a 93 % fusion rate for strut grafts versus Fig. 3 a Pre-operative MRI of a 53-year-old female with cervical myelopathy. The extruded disc material behind the body of C6 requires a corpectomy for decompression. Options for treating C4–5 include an ACDF at that level or a second corpectomy of C5. b Post-operative lateral radiograph 1 year after a hybrid type procedure with an ACDF at C4–5 and a one-level corpectomy of C6 with strut grafting and anterior plating
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66 % for multiple interbody grafts, but only autografts and no instrumentation was used for that retrospective study. Using anterior instrumentation and cages, Liu et al. compared three-level ACDF to hybrid procedures to two-level corpectomy procedures. The union rate was 100, 94.4, and 84.6 %, respectively, with the corpectomy group statistically lower than the other two groups [39]. However, Lin et al. [13], from the same institution just referenced, recorded a 100 % fusion rate in 57 patients undergoing three-level ACDF and 63 patients undergoing a two-level corpectomy, all with instrumentation and cages. In a systematic literature review of anterior surgical options for treatment of cervical myelopathy, Shamji et al. [40] found insufficient evidence to recommend one procedure over another with respect to successful arthrodesis, but moderate evidence favoring multiple discectomies over corpectomies regarding clinical outcome and sagittal alignment. Threelevel corpectomy and strut procedures (i.e., spanning four disc levels) have been shown to be inadequately stabilized by anterior plating alone [23, 24] and typically require concomitant posterior stabilization techniques to ensure graft stability, maintenance of sagittal alignment, and successful arthrodesis. More recently, hybrid anterior reconstruction methods have gained popularity when corpectomies are required for decompression. A hybrid technique typically involves a single-level anterior discectomy and fusion in conjunction with a one- or two-level corpectomy and strut graft, followed by anterior plating (Fig. 3). This combination allows for segmental fixation for the anterior plate with screw fixation usually in three vertebral levels. This technique may eliminate the need for a second posterior stabilization procedure and most likely decreases the risk of graft
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complications inherent to longer strut grafts. These advantages have been suggested in some recent studies though outcome data for hybrid techniques is still somewhat limited at this point in time [41–43]. Alternative anterior techniques A technique of oblique corpectomies for anterior decompression without arthrodesis over one or more levels has been described [44, 45]. This method involves an anterolateral approach to the spine, exposure of the vertebral artery, and oblique channeling to remove lateral pathology on the approach side and anterior compressive pathology. Enough of the far lateral and anterior vertebral body is left to maintain stability without arthrodesis. Patients must have collapsed discs with inherently stable spines to be candidates for this approach. Drawbacks include a higher incidence of Horner’s syndrome, risk of vertebral artery injury, and inability to correct kyphosis. Some authors have published case series describing satisfactory results [46, 47], but the technique has not gained wide popularity. Traynelis et al. [48] in a literature review of comparative effectiveness and safety noted insufficient evidence regarding efficacy of oblique corpectomies, and stated it was not a first line option due to increased morbidity. Open window corpectomy is a second alternative anterior technique, described in 1999 by Ozer et al. [49]. This technique removes the entire posterior portion of the vertebral body, but leaves the anterior shell so that interbody type bone grafts can be used for arthrodesis rather than a longer strut graft. The same authors published a retrospective review of 15 patients using this technique with satisfactory results, but the advantages over conventional corpectomy methods are questionable and it is not widely used [50]. Anterior reconstruction and plating techniques For anterior cervical discectomy and fusion procedures, several options exist for interbody bone grafts or graft substitutes. Whereas in years past, autogenous iliac crest graft was considered the gold standard, the advent of anterior plating with better fusion results has led to allograft as the more common type of bone used for ACDF [51, 52]. Samartzis et al. [52] published a retrospective series comparing instrumented autograft versus allograft for twoand three-level ACDF patients. There was no statistical difference in fusion rates, with 94.3 % of allografts and 100 % of autografts radiographically healed. The number of levels did not affect the union rate in this study, but other authors [25, 26, 35] have shown that three-level ACDF procedures are still problematic as discussed earlier. This
author recommends autograft for select cases such as anterior pseudarthrosis repairs or primary cases in heavy smokers. Bone graft substitutes such as polyetheretherketone (PEEK) cages or titanium mesh cages have also been used for cervical interbody procedures with reported good results [53]. Ba et al. [54] reported on 207 ACDF patients using PEEK, anterior plating, and local autograft with a CT scan proven 100 % fusion rate. Petr et al. [51] also noted a 100 % fusion rate with PEEK, plating, and local autograft. Concomitant use of bone grafting material in the cage device seems important, as Pechlivanis et al. [55] documented 28 % of levels went on to nonunion when only the PEEK cage and anterior plate alone (nothing in the center) were used for the interbody spacer. Using interbody titanium cages alone (no anterior instrumentation) in one- and two-level ACDF patients, Niu et al. [53] reported an 86.5 % fusion rate but noted 16.3 % of interspaces settled more than 3 mm. Uribe et al. [56] had better results using titanium mesh cages and anterior plating for multi-level interbody constructs with a 97.6 % fusion rate and excellent clinical outcomes. Anterior reconstruction using longer strut grafts is required following multi-level corpectomy procedures. Fibula allograft or titanium cage devices packed with bone seem to be most widely used. Some settling is to be expected in this patient population as many with cervical spondylotic myelopathy are older and may have osteoporosis [36]. The evolution of anterior cervical plate designs allows surgeons the options of rigid, semi-rigid, and translational fixation devices. Locked screw–plate designs provide maximum segmental stability, but resist load sharing on the anterior bone graft or cage which may hinder healing [57]. Semi-rigid constructs allow for screw rotation to some degree in the sagittal plane at the screw–plate interface, allowing for some interbody graft compression without sacrificing too much stability. Translational plates allow vertical shortening of the construct, either via screws sliding vertically within the plate or the plate itself collapsing slightly to shorten. Studies have shown that, in general, these plates will behave as designed and the surgeon should be aware of the advantages and disadvantages for any given patient [58, 59]. One study noted an increase in segmental kyphosis in patients with translational type plates but had a higher healing rate and satisfactory outcomes. Rigid plates had less settling but a higher pseudarthrosis rate with screw breakage [60]. Semi-rigid constructs that allow for bone graft settling can also lead to impingement of the leading edge of the plate on annulus of the disc above the construct. A beak of bone formation at that adjacent annulus has been termed Adjacent Level Ossification Disease (ALOD) [61]
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Eur Spine J Fig. 4 a Lateral radiograph early post-operatively after a C6 corpectomy, strut graft, and anterior plating. A hemicorpectomy was necessary of the lower half of the C5 body, thus the superior edge of the plate is in contact with the annulus above. b A lateral radiograph 6 years postoperatively shows substantial beaking at the adjacent disc and vertebral body, from adjacent level ossification disease (ALOD)
and requires technical awareness to avoid if possible (Fig. 4). More recently, zero profile PEEK implants with screws angled superiorly and inferiorly into the endplates have been utilized for arthrodesis [62], though no studies exist describing their use in patients with cervical myelopathy. These implants provide some advantage if an ACDF is required above a remote plated arthrodesis, as they offer screw fixation and a load-bearing graft without having to remove the existing plate. As discussed earlier, anterior cervical plating alone seems unable to stabilize strut graft constructs following three or more level corpectomy procedures, and different strategies such as hybrid techniques or circumferential stabilization are recommended. Disc arthroplasty offers an alternative to ACDF although its use in patients with cervical myelopathy has not been well studied. Since the current recommendations for use of disc arthroplasty is in younger patients with strong endplates, no facet arthritis, and less than severe spondylotic changes, many patients with myelopathy fall outside these parameters. Some spine surgeons believe operative treatment for a compromised spinal cord warrants arthrodesis at that motion segment in order to maximize protection of the cord. Buchowski et al. [63], however, demonstrated good clinical results after disc arthroplasty for myelopathy patients with one-level disease as part of an FDA investigational trial in the US. Cervical spondylosis, and thus cervical myelopathy, will continue to require the attention of the spine community worldwide. There is a lack of robust evidence-based medicine to help guide surgical decision-making in the operative treatment of cervical spondylotic myelopathy. There remains substantial basic science and clinical investigation needed regarding pharmacologic treatment, anterior versus posterior approaches, hybrid results, bone
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graft substitutes and the role of the disc arthroplasty for this disease entity. Conflict of interest interest.
None of the authors has any potential conflict of
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25. Bolesta MJ, Rechtine GR 2nd, Chrin AM (2000) Three- and fourlevel cervical discectomy and fusion with plate fixation: a prospective study. Spine 25:2040–2044 26. Wang JC, McDonough PW, Kanim LE, Endow KK, Delamarter RB (2001) Increased fusion rates with cervical plating for threelevel anterior cervical discectomy and fusion. Spine 26:643–646 27. Emery SE, Akhavan S, Miller P, Furey CG, Yoo JU, Rowbottom JR, Bohlman HH (2009) Steroids and risk factors for airway compromise in multilevel cervical corpectomy patients: a prospective, randomized, double-blind study. Spine 34:229–232 28. Bazaz R, Lee MJ, Yoo JU (2002) Incidence of dysphagia after anterior cervical spine surgery: a prospective study. Spine 27:2453–2458 29. Lee MJ, Bazaz R, Furey CG, Yoo J (2007) Risk factors for dysphagia after anterior cervical spine surgery: a two-year prospective cohort study. Spine J 7:141–147 30. Riley LH 3rd, Skolasky RL, Albert TJ, Vaccaro AR, Heller JG (2005) Dysphagia after anterior cervical decompression and fusion: prevalence and risk factors from a longitudinal cohort study. Spine 30:2564–2569 31. Sakaura H, Hosano N, Mukai Y, Fujimori T, Iwasaki M, Yoshikawa H (2010) Preservation of muscles attached to the C2 and C7 spinous processes rather than subaxial deep extensors reduces adverse effects after cervical laminoplasty. Spine 35:E782–E786 32. Iwasaki M, Okuda S, Miyauchi A, Sakaura H, Mukai Y, Yonenobu K, Yoshikawa H (2007) Surgical strategy for cervical myelopathy due to ossification of the posterior longitudinal ligament: part 2: Advantages of anterior decompression and fusion over laminoplasty. Spine 32:654–660 33. Arvin B, Kalsi-Ryan S, Mercier D, Furlan JC, Massicotte EM, Fehlings MG (2013) Preoperative magnetic resonance imaging is associated with baseline neurological status and can predict recovery in patients with cervical spondylotic myelopathy. Spine 38:1170–1176 34. Karpova A, Arun R, Cadotte DW, Davis AM, Kulkarni AV, O’Higgins M, Fehlings MG (2013) Assessment of spinal cord compression by magnetic resonance imaging—can it predict surgical outcomes in degenerative compressive myelopathy—a systematic review. Spine 28:1409–1421 35. Fraser JF, Ha¨rtl R (2007) Anterior approaches to fusion of the cervical spine: a metaanalysis of fusion rates. J Neurosurg Spine 6:298–303 36. Hughes SS, Pringle T, Phillips F, Emery S (2006) Settling of fibula strut grafts following multilevel anterior cervical corpectomy: a radiographic evaluation. Spine 31:1911–1915 37. Hosono N, Yonenobu K, Ono K (1996) Neck and shoulder pain after laminoplasty. A noticeable complication. Spine 21:1969–1973 38. Hilibrand AS, Fye MA, Emery SE, Palumbo MA, Bohlman HH (2002) Increased rate of arthrodesis with strut grafting after multilevel anterior cervical decompression. Spine 27:146–151 39. Liu Y, Hou Y, Yang L, Chen H, Wang X, Wu X, Gao R, Wang C, Yuan W (2012) Comparison of 3 reconstructive techniques in the surgical management of multilevel cervical spondylotic myelopathy. Spine 37:E1450–E1458 40. Shamji MF, Massicotte EM, Traynelis VC, Norvell DC, Hermsmeyer JT, Fehlings MG (2013) Comparison of anterior surgical options for the treatment of multilevel cervical spondylotic myelopathy: a systematic review. Spine 38:S195–S209 41. Guo Q, Bi X, Ni B, Lu X, Chen J, Yang J, Yu Y (2011) Outcomes of three anterior decompression and fusion techniques in the treatment of three-level cervical spondylosis. Eur Spine J 20:1539–1544 42. Wei-bing X, Wun-Jer S, Gang L, Yue Z, Ming-xi J, Lian-shun J (2009) Reconstructive techniques study after anterior decompression of multilevel cervical spondylotic myelopathy. J Spinal Disord Tech 22:511–515
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Eur Spine J 43. Liu Y, Qi M, Chen H, Yang L, Wang X, Shi G, Gao R, Wang C, Yuan W (2012) Comparative analysis of complications of different reconstructive techniques following anterior decompression for multilevel cervical spondylotic myelopathy. Eur Spine J 21(12):2428–2435 44. George B, Gauthier N, Lott G (1999) Multisegmental cervical spondylotic myelopathy and radiculopathy treated by multilevel oblique corpectomies without fusion. Neurosurgery 44:81–90 45. Bruneau M, Cornelius JF, George B (2007) Multilevel oblique corpectomies: surgical indications and technique. Neurosurgery 61(3 Suppl):106–112 46. Chibbaro S, Mirone G, Makiese O, George B (2009) Multilevel oblique corpectomy without fusion in managing cervical myelopathy: long-term outcome and stability evaluation in 268 patients. J Neurosurg Spine 10:458–465 47. Rocchi G, Caroli E, Salvati M (2005) Multilevel oblique corpectomy without fusion: our experience in 48 patients. Spine 30:1963–1969 48. Traynelis VC, Arnold PM, Fourney DR, Bransford RJ, Fischer DJ, Skelly AC (2013) Alternative procedures for the treatment of cervical spondylotic myelopathy: arthroplasty, oblique corpectomy, skip laminectomy: evaluation of comparative effectiveness and safety. Spine 38(22 Suppl 1):S210–S231 49. Ozer AF, Oktenog˘lu BT, Sariog˘lu AC (1999) A new surgical technique: open-window corpectomy in the treatment of ossification of the posterior longitudinal ligament and advanced cervical spondylosis: technical note. Neurosurgery 45:1481–1486 50. Ozer AF, Oktenoglu T, Cosar M, Sasani M, Sarioglu AC (2009) Long-term follow-up after open-window corpectomy in patients with advanced cervical spondylosis and/or ossification of the posterior longitudinal ligament. J Spinal Disord Tech 22:14–20 51. Vanek P, Bradac O, DeLacy P, Saur K, Belsan T, Benes V (2012) Comparison of 3 fusion techniques in the treatment of the degenerative cervical spine disease. Is stand-alone autograft really the ‘‘gold standard?’’: prospective study with 2-year follow-up. Spine 37(19):1645–1651 52. Samartzis D, Shen FH, Matthews DK, Yoon ST, Goldberg EJ, An HS (2003) Comparison of allograft to autograft in multilevel anterior cervical discectomy and fusion with rigid plate fixation. Spine J 3:451–459 53. Niu CC, Liao JC, Chen WJ, Chen LH (2010) Outcomes of interbody fusion cages used in 1 and 2-levels anterior cervical
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ORIGINAL ARTICLE
Anterior approaches for cervical spondylotic myelopathy: Which? When? How? Sanford E. Emery
Received: 30 November 2012 / Revised: 27 January 2015 / Accepted: 27 January 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract Cervical spondylotic myelopathy is a degenerative disorder with an unfavorable natural history. Surgical treatment options have evolved substantially over time, with both anterior and posterior methods proving successful for certain patients with specific characteristics. Anterior decompression of the spinal canal plus fusion techniques for stabilization has several advantages and some disadvantages when compared to posterior options. Understanding the pros and cons of the approaches and techniques is critical for the surgeon to select the best operative treatment strategy for any given patient to achieve the best outcome. Multiple decision-making factors are involved, such as sagittal alignment, number of levels, shape of the pathoanatomy, age and comorbidities, instability, and pre-operative pain levels. Any or all of these factors may be relevant for a given patient, and to varying degrees of importance. Choice of operative approach will therefore be dependent on patient presentation, risks of that approach for a given patient, and to some degree surgeon experience. Keywords Cervical myelopathy Anterior approach cervical spine Anterior cervical discectomy and fusion Anterior cervical corpectomy and fusion
Introduction The operative treatment of cervical spondylotic myelopathy has evolved over several decades, and today there is S. E. Emery (&) Department of Orthopaedics, West Virginia University, PO Box 9196, Morgantown, WV 26506-9196, USA e-mail: [email protected]
often more than one option for obtaining successful outcomes in this patient population. After clarification of the clinical entity of cervical myelopathy, largely in the literature of the 1950s from pathoanatomic studies, the posterior approach with multi-level laminectomies was initially utilized. The anterior approach became more widely accepted in the 1970s and 1980s, probably due to better characterization of the pathoanatomy of cord compression offered by CT myelography and later by magnetic resonance imaging. Beginning in Japan in the late 1970s and 1980s, laminoplasty was developed as an operative method followed by laminectomy and fusion when improved posterior cervical instrumentation became available.
Methods The review of the literature was undertaken using the PubMed.gov vehicle. The keywords entered into the search were ‘‘cervical myelopathy’’ AND ‘‘anterior surgery’’. This yielded 1,635 abstracts in the English language which were reviewed by the author. The search timeframe was from 1963 to 2013. Sixty-five articles were chosen by the author and reviewed for their relevance regarding the anterior versus posterior approach for cervical spondylotic myelopathy and anterior reconstructive techniques in the cervical spine. Advantages of the anterior approach for cervical spondylotic myelopathy The anterior approach to the spine using a standard Smith– Robinson technique is quite safe and straightforward for the trained spine surgeon. Potential complications will be
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discussed below, but serious complications are quite uncommon. The main advantages of the anterior operative approach for this disorder include: Direct removal of the compressive pathology In the vast majority of cases, compression of the cervical cord producing myelopathy stems from anterior pathology such as disc herniations, osteophytic changes, kyphosis, and subluxation. The anterior approach allows for removal of the compression, either with a simple discectomy or larger decompression techniques such as hemicorpectomy, corpectomy, or multi-level corpectomies. Foraminotomies can be successfully performed from an anterior approach as well by decompressing or totally removing the uncovertebral joint areas. With direct removal of the pathology, one might expect better neurologic recovery. This topic has been studied with conflicting results. In many scientific articles, the neurologic outcome for myelopathy with or without radiculopathy has at least been as good as posterior procedures or, in some studies, slightly better [1–5]. In one 10-year follow-up study of corpectomies versus laminoplasty, neurologic outcome remained equivalent in both groups [6]. Cunningham et al. [7] in a review of 11 cohort studies also found similar neurologic outcomes for anterior versus posterior groups. However, Hirai et al. [1] looked at their experience with anterior versus posterior cohorts and found better neurologic recovery in the anterior group, particularly with respect to upper extremity function. Less recovery in the posterior group was believed to be due to residual anterior cord compression. Mummaneni et al. [8] in a thorough literature review, noted similar neurologic outcomes for the two approaches in spondylotic myelopathy patients, with the exception of late deterioration evident in the laminectomy alone outcomes. A recent meta-analysis of ten articles focused on anterior versus posterior approaches for treatment of myelopathy suggested neurologic recovery was equivalent if the occupying ratio of canal compromise was \60 % [9]. Of note is that this review included studies of OPLL, and reportedly included few if any laminectomy plus fusion patients. Another metaanalysis of eight studies for spondylotic myelopathy patients did include anterior, laminoplasty, and laminectomy plus fusion groups [10]. These authors found better neural recovery with anterior decompression and arthrodesis at the cost of a higher complication rate. Fehlings et al. [11] recently published the outcomes of the prospective, multi-center study of cervical spondylotic myelopathy patients from the AOSpine consortium comparing anterior vs. posterior approaches. One hundred sixty-nine patients underwent anterior surgery and 95 posterior surgery (mostly laminectomy and fusion).
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Multiple validated outcome measures were utilized. Though the choice of technique depended on surgeon preference, multivariate analysis methods were used to control for baseline confounders. The results demonstrated that anterior and posterior approaches had equivalent beneficial outcomes in the treatment of cervical spondylotic myelopathy. Complication rates were also equivalent, with the exception being a trend toward a higher infection rate in posterior surgeries. Correction of deformity Anterior discectomies or corpectomies with bone graft or cage reconstruction will allow for correction of cervical kyphosis, which is by far the most common deformity seen in this patient population. Uchida et al. [12] compared patients with pre-operative kyphosis [10° who underwent either anterior corpectomy or laminoplasty procedures for spondylotic myelopathy. Average kyphosis decreased 46 % in the anterior group and 15 % in the laminoplasty group. Discectomies with interbody fusion have been shown to statistically correct kyphosis better than corpectomy and strut graft procedures (post-operative lordosis of 17.6 vs. 14.5 degrees, respectively) [13]. Along with neural decompression, achieving satisfactory sagittal balance is a tenet of surgical treatment for cervical myelopathy [14]. Flexible kyphotic deformities may be amenable to posterior decompressions with an instrumented fusion holding them back in an acceptable position, but more rigid kyphotic deformities will typically require at least an anterior approach and, at times, a circumferential strategy [15]. Arthrodesis Fusion of the cervical spine can, of course, be a doubleedged sword with potential future complications of adjacent segment degeneration. Hilibrand et al. in a retrospective review of 374 patients calculated a 2.9 % incidence per year of symptomatic adjacent segment disease in patients with prior cervical arthrodesis. At 10 years, the prevalence was 25 % [16]. Nunley et al. looked at radiographic adjacent segment changes in 170 patients in both an anterior fusion group and disc arthroplasty group of a randomized study. At a median follow-up of 42 months (range 28–54 months), adjacent radiographic changes occurred in 14.3 % of the fusion group and 16.8 % of the arthroplasty group [17]. Though not without potential downstream side effects, arthrodesis remains a critical strategy for patients with instability or cervical kyphosis. Anterior arthrodesis techniques may have the potential benefit of distraction with indirect opening of the foramen compared to posterior fusion techniques. Either approach, having obtained a successful fusion, will provide good
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relief of axial neck pain in most patients [3]. Wada et al. [6] documented only 15 % of patients with neck pain 10 years after anterior corpectomy and arthrodesis for myelopathy vs. 40 % in a laminoplasty group. Ghogawala et al.[18] documented improvement in the Neck Disability Index, a validated questionnaire measuring neck pain, for both posterior fusion and anterior fusion groups in his comparative study on myelopathy patients, with the best results vs. baseline symptoms in the anterior group. Though both groups were posterior approach techniques, Hightower et al. [19] noted no improvement in pre-operative visual analog (VAS) pain scores for a laminoplasty group but statistically significant improvement in VAS scores in a posterior laminectomy and fusion group, suggesting arthrodesis can help neck pain. Disadvantages of the anterior approach for cervical spondylotic myelopathy There are certain downsides of the anterior operative approach compared to posterior options: Higher complication rates Multi-level anterior procedures are more technically demanding than posterior options. Two- or three-level anterior corpectomy procedures will typically take longer and encounter more blood loss than, for example, a multilevel laminoplasty procedure [6]. Several studies have noted an increased rate of complications for anterior patients. Edwards et al. [20] in a small study of matched cohorts found more complications including nonunion, persistent dysphagia and dysphonia, and adjacent segment problems in the multi-level corpectomy group. Fehlings et al. [21] in a multi-center prospective study of spondylotic myelopathy patients found the risk of peri-operative complications to be related to age, combined anterior–posterior procedures, increased operative time, and blood loss but not anterior versus posterior approaches alone. Hirai et al. [1] documented more complications in their anterior cohort group, including airway issues, dysphagia, and pseudarthrosis versus the laminoplasty group. Three systematic reviews of cohort studies also concluded that post-operative complications are greater for multi-level anterior surgical approaches compared to posterior options [7, 9, 10]. Interestingly, the well-studied but not well understood C5 root palsy complication can occur after either anterior or posterior treatment of cervical myelopathy. Historically, studies documented the incidence anywhere from 4 to 16 % in laminoplasty patients, and it was initially associated with that specific procedure. More recently, however, studies have noted similar rates in anterior corpectomy patients [22] or equivalent rates in cohort studies [1].
Strut graft/interbody reconstruction Meticulous technique (i.e., good carpentry!) is very important for the stability and healing potential of anterior strut graft reconstruction. Migration or dislodgement of long struts is enough of a risk that many surgeons utilize a circumferential procedure for three or more level corpectomy patients [23, 24], and even some two-level corpectomy patients with kyphosis or severe osteoporosis. Longer term risks of pseudarthrosis can be significant for multilevel anterior cervical discectomy and fusion (ACDF) procedures even with anterior plating [25, 26]. Dysphagia and airway issues Though airway complications can occur at any time, they are more problematic in long anterior corpectomy and reconstruction procedures [27]. In recent years, dysphagia has been documented to be more common than previously thought for the anterior approach. The vast majority of swallowing symptoms resolve relatively quickly, but can be persistent for years in a small percentage of patients [28–30]. Bazaz et al. [28] documented some degree of dysphagia 6 months following anterior cervical arthrodesis in 208 patients, with mild difficulty reported by 17.8 % of patients, moderate by 4.3 %, and severe by one patient. Loss of motion and post-operative bracing Many discectomy and fusion patients and all multi-level corpectomy patients require some form of post-operative bracing to help maintain stability in the early post-operative period and encourage successful arthrodesis. Bracing is used by many surgeons to help maintain stability in the early post-operative period and encourage a successful arthrodesis. High-quality studies that would offer evidence-based guidelines regarding the need for a brace, type or duration of bracing after anterior procedures is lacking. Of course, arthrodesis is designed to immobilize the operative segments of the spine and will inherently decrease range of motion, depending on the number of levels fused. Though earlier studies demonstrated substantial loss of mobility after laminoplasty [6], more recent attention to early range of motion post-operatively and less bracing has minimized loss of motion after laminoplasty [31]. Decision-making considerations Given the relative advantages and disadvantages of the anterior approach for cervical spondylotic myelopathy, for any given patient the surgeon should consider the following factors:
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Sagittal alignment of the cervical spine As mentioned, a flexible deformity may be successfully treated with posterior decompression and stabilization in a satisfactory position but, generally speaking, cervical kyphosis, particularly fixed kyphosis, warrants anterior decompression and stabilization techniques. Uchida et al. [12] noted less neurologic improvement in patients with 10° or more of kyphosis if treated with laminoplasty. Pathoanatomy Though the paper concerned OPLL patients, Iwasaki et al. [32] showed that hill-shaped lesions responded better to anterior decompression, and more flat type of compression did well with laminoplasty. In that study, if the compression ratio was [60 %, patients had better neurologic recovery with anterior decompression than laminoplasty. If we extrapolate this finding to spondylotic myelopathy patients, then disc protrusions or osteophytes that jut into the spinal cord causing a kidney bean type of anterior deformation are perhaps best treated with an anterior technique in order to adequately decompress the cord. More of a generalized stenosis where there is flattening of the anterior cord may be amenable to either posterior or anterior decompression procedures [32]. Though not as common as anterior cord compression, infolding of the ligamentum flavum with posterior canal compromise may warrant a posterior approach for any given patient. Intra-parenchymal signal change of the spinal cord in the setting of cervical myelopathy is believed to result from chronic compression causing myelomalacia. A recent study by Arvin et al. [33] looked at 57 patients prospectively and concluded that MRI signal changes, such as increased T2 signal and low T1 signal, were predictors of initial neurological status and post-operative recovery. In a systematic review of the literature, Karpova et al. [34] investigated the value of signal change and other factors on predicting surgical outcomes. The authors also concluded that signal changes could help predict surgical outcomes in spondylotic myelopathy. Although these studies and others suggest that signal change may be important for surgical indications and post-operative recovery, there is no data in the literature to suggest anterior approaches are better or worse than posterior approaches for the operative treatment of myelopathy in this subpopulation of patients. Number of levels involved In Fraser’s meta-analysis, for three levels of pathology, anterior cervical discectomy and interbody techniques will have a lower rate of successful arthrodesis than one- or
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two-level interbody procedures and lower than corpectomy procedures [35]. Multi-level corpectomies with strut reconstruction are more demanding for the surgeon and the patient and may require circumferential stabilization. For a given patient with myelopathy with other factors being equivalent, the number of operative levels is often the deciding factor for choice of operative approach. Subluxation or instability If degenerative changes have led to subluxation of specific segments or certainly with dynamic instability, arthrodesis is indicated. Instability requiring operative stabilization may be difficult to define in the spondylotic patient with myelopathy, which is a different population than those with acute trauma. Generally, 2 mm of translational motion is acceptable in these patients and 4 mm may warrant surgery, though other factors such as the size of their spinal canal, pain symptoms, and medical condition are important. No evidence-based literature defines operative indications for a specific amount of motion, to this author’s knowledge. Bone quality Severe osteoporosis can be problematic due to long strut graft settling [36] as well as difficulty achieving stable fixation with anterior plates. This potential complication may tip the scales for posterior laminoplasty procedures if other factors make that a reasonable option. Neck pain Though not well elucidated in the literature to date, the amount of pre-operative neck pain displayed by any given patient does play into the decision of operative approach. By definition, patients with cervical spondylotic myelopathy usually have significant spondylosis and disc degeneration, which often is a main contributor to their cord compression. Though the source of axial neck pain is not totally understood, in a patient with moderate-to-severe neck pain and significant degenerative changes, this author would recommend fusion as part of the operative treatment, rather than just a decompression such as laminoplasty. Liu et al. [9] in their meta-analysis of anterior vs. posterior studies found no differences in axial pain outcomes, but noted that only two of the ten studies reviewed actually reported pain outcomes. Cunningham et al. [7] in their literature review concluded that laminoplasty patients had more post-operative neck pain, but they quoted older studies where bracing, prolonged immobilization, and opening the C7 lamina were standard methods [6, 37].
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Risks and patient factors Knowing the pros and cons of anterior and posterior approaches, the surgeon must consider the particular patient and apply that knowledge to that individual. A patient having had multiple prior anterior approaches or previous recurrent laryngeal nerve palsy is probably a better candidate for a posterior surgical approach. The frail,
elderly patient with chronic obstructive pulmonary disease may steer us away from a multi-level corpectomy and strut graft procedure where airway and swallowing issues could be problematic post-operatively. Patients with severe spondylosis, significant neck pain, and focal disc herniations at one or two levels with frank deformity of the spinal cord are excellent candidates for an anterior approach with a two-level discectomy and fusion. The choice of operative procedure for the treatment of cervical spondylotic myelopathy is partly art and partly science. Some patients are better candidates for either an anterior or a posterior technique, whereas many others can be successfully treated with either approach, as graphically summarized in Fig. 1. A horizontal flow chart is offered (Fig. 2) as an aid for the surgeon to consider the options for any given patient. Though this chart is ‘‘linear’’ in presentation, in reality it is more of a matrix thought process since the decision-making parameters may be weighted differently in an actual clinical situation. Selection of anterior operative techniques
Fig. 1 Diagram illustrating patient selection for anterior versus posterior approaches for surgical treatment of cervical myelopathy. (Reprinted with permission from The Cervical Spine, 5th edition, Benzel et al. eds. Lippincott, Williams and Wilkins, 2012, p. 1012.)
Anterior decompression and fusion procedures can be placed in three categories: (a) discectomy and fusion techniques; (b) corpectomy and strut grafting techniques,
Fig. 2 Flow chart for decision-making in the choice of operative approach and technique. This list of factors the surgeon should consider may be weighted differently for any particular patient, thus a ‘‘blended’’ cost–benefit analysis requires surgeon judgment
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and (c) hybrid procedures. Discectomy and fusion procedures involve removing the disc and any posterior osteophytes in order to obtain decompression of the canal. This procedure is quite adequate for soft disc herniations provided they have not migrated cephalad or caudad behind vertebral bodies. More spondylotic changes of the endplates may require partial corpectomies in order to adequately decompress the spinal canal, using slightly taller strut grafts or cages to provide anterior stabilization and ultimate arthrodesis. If the pathoanatomy of the cord compression is amenable to discectomy and fusion at the necessary levels, then this technique actually gives better correction of cervical kyphosis than does multi-level corpectomy techniques since distraction is over several segments [13]. There is a documented pseudarthrosis rate of 18 % or higher with a three or more level ACDF [25, 26, 35], however, so this needs to be taken into account when considering choice of technique and host factors. Corpectomy and strut graft techniques are ideal for decompressing the spinal canal when there is spinal cord compression behind the vertebral bodies. A corpectomy allows the surgeon to come down directly on the pathoanatomy and safely remove it. At times, when there are large osteophytic changes at the endplates over multiple segments and severe cord compression, this author believes it is safer to perform corpectomies in order to avoid neurologic complications and ensure adequate decompression over several levels than to attempt limited discectomies at each level. Strut grafting over multiple levels does limit the number of surfaces requiring osseous healing, though it is unclear this lowers the nonunion rate compared to multilevel discectomy and interbody grafting. Hilibrand et al. [38] documented a 93 % fusion rate for strut grafts versus Fig. 3 a Pre-operative MRI of a 53-year-old female with cervical myelopathy. The extruded disc material behind the body of C6 requires a corpectomy for decompression. Options for treating C4–5 include an ACDF at that level or a second corpectomy of C5. b Post-operative lateral radiograph 1 year after a hybrid type procedure with an ACDF at C4–5 and a one-level corpectomy of C6 with strut grafting and anterior plating
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66 % for multiple interbody grafts, but only autografts and no instrumentation was used for that retrospective study. Using anterior instrumentation and cages, Liu et al. compared three-level ACDF to hybrid procedures to two-level corpectomy procedures. The union rate was 100, 94.4, and 84.6 %, respectively, with the corpectomy group statistically lower than the other two groups [39]. However, Lin et al. [13], from the same institution just referenced, recorded a 100 % fusion rate in 57 patients undergoing three-level ACDF and 63 patients undergoing a two-level corpectomy, all with instrumentation and cages. In a systematic literature review of anterior surgical options for treatment of cervical myelopathy, Shamji et al. [40] found insufficient evidence to recommend one procedure over another with respect to successful arthrodesis, but moderate evidence favoring multiple discectomies over corpectomies regarding clinical outcome and sagittal alignment. Threelevel corpectomy and strut procedures (i.e., spanning four disc levels) have been shown to be inadequately stabilized by anterior plating alone [23, 24] and typically require concomitant posterior stabilization techniques to ensure graft stability, maintenance of sagittal alignment, and successful arthrodesis. More recently, hybrid anterior reconstruction methods have gained popularity when corpectomies are required for decompression. A hybrid technique typically involves a single-level anterior discectomy and fusion in conjunction with a one- or two-level corpectomy and strut graft, followed by anterior plating (Fig. 3). This combination allows for segmental fixation for the anterior plate with screw fixation usually in three vertebral levels. This technique may eliminate the need for a second posterior stabilization procedure and most likely decreases the risk of graft
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complications inherent to longer strut grafts. These advantages have been suggested in some recent studies though outcome data for hybrid techniques is still somewhat limited at this point in time [41–43]. Alternative anterior techniques A technique of oblique corpectomies for anterior decompression without arthrodesis over one or more levels has been described [44, 45]. This method involves an anterolateral approach to the spine, exposure of the vertebral artery, and oblique channeling to remove lateral pathology on the approach side and anterior compressive pathology. Enough of the far lateral and anterior vertebral body is left to maintain stability without arthrodesis. Patients must have collapsed discs with inherently stable spines to be candidates for this approach. Drawbacks include a higher incidence of Horner’s syndrome, risk of vertebral artery injury, and inability to correct kyphosis. Some authors have published case series describing satisfactory results [46, 47], but the technique has not gained wide popularity. Traynelis et al. [48] in a literature review of comparative effectiveness and safety noted insufficient evidence regarding efficacy of oblique corpectomies, and stated it was not a first line option due to increased morbidity. Open window corpectomy is a second alternative anterior technique, described in 1999 by Ozer et al. [49]. This technique removes the entire posterior portion of the vertebral body, but leaves the anterior shell so that interbody type bone grafts can be used for arthrodesis rather than a longer strut graft. The same authors published a retrospective review of 15 patients using this technique with satisfactory results, but the advantages over conventional corpectomy methods are questionable and it is not widely used [50]. Anterior reconstruction and plating techniques For anterior cervical discectomy and fusion procedures, several options exist for interbody bone grafts or graft substitutes. Whereas in years past, autogenous iliac crest graft was considered the gold standard, the advent of anterior plating with better fusion results has led to allograft as the more common type of bone used for ACDF [51, 52]. Samartzis et al. [52] published a retrospective series comparing instrumented autograft versus allograft for twoand three-level ACDF patients. There was no statistical difference in fusion rates, with 94.3 % of allografts and 100 % of autografts radiographically healed. The number of levels did not affect the union rate in this study, but other authors [25, 26, 35] have shown that three-level ACDF procedures are still problematic as discussed earlier. This
author recommends autograft for select cases such as anterior pseudarthrosis repairs or primary cases in heavy smokers. Bone graft substitutes such as polyetheretherketone (PEEK) cages or titanium mesh cages have also been used for cervical interbody procedures with reported good results [53]. Ba et al. [54] reported on 207 ACDF patients using PEEK, anterior plating, and local autograft with a CT scan proven 100 % fusion rate. Petr et al. [51] also noted a 100 % fusion rate with PEEK, plating, and local autograft. Concomitant use of bone grafting material in the cage device seems important, as Pechlivanis et al. [55] documented 28 % of levels went on to nonunion when only the PEEK cage and anterior plate alone (nothing in the center) were used for the interbody spacer. Using interbody titanium cages alone (no anterior instrumentation) in one- and two-level ACDF patients, Niu et al. [53] reported an 86.5 % fusion rate but noted 16.3 % of interspaces settled more than 3 mm. Uribe et al. [56] had better results using titanium mesh cages and anterior plating for multi-level interbody constructs with a 97.6 % fusion rate and excellent clinical outcomes. Anterior reconstruction using longer strut grafts is required following multi-level corpectomy procedures. Fibula allograft or titanium cage devices packed with bone seem to be most widely used. Some settling is to be expected in this patient population as many with cervical spondylotic myelopathy are older and may have osteoporosis [36]. The evolution of anterior cervical plate designs allows surgeons the options of rigid, semi-rigid, and translational fixation devices. Locked screw–plate designs provide maximum segmental stability, but resist load sharing on the anterior bone graft or cage which may hinder healing [57]. Semi-rigid constructs allow for screw rotation to some degree in the sagittal plane at the screw–plate interface, allowing for some interbody graft compression without sacrificing too much stability. Translational plates allow vertical shortening of the construct, either via screws sliding vertically within the plate or the plate itself collapsing slightly to shorten. Studies have shown that, in general, these plates will behave as designed and the surgeon should be aware of the advantages and disadvantages for any given patient [58, 59]. One study noted an increase in segmental kyphosis in patients with translational type plates but had a higher healing rate and satisfactory outcomes. Rigid plates had less settling but a higher pseudarthrosis rate with screw breakage [60]. Semi-rigid constructs that allow for bone graft settling can also lead to impingement of the leading edge of the plate on annulus of the disc above the construct. A beak of bone formation at that adjacent annulus has been termed Adjacent Level Ossification Disease (ALOD) [61]
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Eur Spine J Fig. 4 a Lateral radiograph early post-operatively after a C6 corpectomy, strut graft, and anterior plating. A hemicorpectomy was necessary of the lower half of the C5 body, thus the superior edge of the plate is in contact with the annulus above. b A lateral radiograph 6 years postoperatively shows substantial beaking at the adjacent disc and vertebral body, from adjacent level ossification disease (ALOD)
and requires technical awareness to avoid if possible (Fig. 4). More recently, zero profile PEEK implants with screws angled superiorly and inferiorly into the endplates have been utilized for arthrodesis [62], though no studies exist describing their use in patients with cervical myelopathy. These implants provide some advantage if an ACDF is required above a remote plated arthrodesis, as they offer screw fixation and a load-bearing graft without having to remove the existing plate. As discussed earlier, anterior cervical plating alone seems unable to stabilize strut graft constructs following three or more level corpectomy procedures, and different strategies such as hybrid techniques or circumferential stabilization are recommended. Disc arthroplasty offers an alternative to ACDF although its use in patients with cervical myelopathy has not been well studied. Since the current recommendations for use of disc arthroplasty is in younger patients with strong endplates, no facet arthritis, and less than severe spondylotic changes, many patients with myelopathy fall outside these parameters. Some spine surgeons believe operative treatment for a compromised spinal cord warrants arthrodesis at that motion segment in order to maximize protection of the cord. Buchowski et al. [63], however, demonstrated good clinical results after disc arthroplasty for myelopathy patients with one-level disease as part of an FDA investigational trial in the US. Cervical spondylosis, and thus cervical myelopathy, will continue to require the attention of the spine community worldwide. There is a lack of robust evidence-based medicine to help guide surgical decision-making in the operative treatment of cervical spondylotic myelopathy. There remains substantial basic science and clinical investigation needed regarding pharmacologic treatment, anterior versus posterior approaches, hybrid results, bone
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graft substitutes and the role of the disc arthroplasty for this disease entity. Conflict of interest interest.
None of the authors has any potential conflict of
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