|SYMPOSIUM - CERVICAL SPONDYLOMYELOPATHY
|Year : 2019 | Volume
| Issue : 1 | Page : 59-67
Clinical predictors of complications and outcomes in degenerative cervical myeloradiculopathy
Jamie R F Wilson1, Fan Jiang1, Michael G Fehlings2
1 Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
2 Division of Neurosurgery, Toronto Western Hospital, University Health Network; Department of Surgery, University of Toronto, Toronto, ON, Canada
|Date of Web Publication||11-Jan-2019|
Dr. Michael G Fehlings
Division of Neurosurgery and Spinal Program, Toronto Western Hospital, 399 Bathurst Street, Suite 4W-449, Toronto, ON
Source of Support: None, Conflict of Interest: None
Degenerative cervical myelopathy (DCM) is the leading cause of adult spinal cord dysfunction worldwide, and surgical decompression remains the mainstay treatment to arrest the progression of neurological deterioration. A number of clinical factors can predict and influence the outcomes of surgery, including patient demographics, baseline myelopathy severity, duration of symptoms, imaging characteristics, and types of surgical approach. Understanding the influence and relationship of these factors on surgical outcomes allows the treating clinician the ability to provide the patient with realistic expectations when discussing surgical intervention for DCM.
Keywords: Complications, degenerative cervical myelopathy, outcomes, predictors
|How to cite this article:|
Wilson JR, Jiang F, Fehlings MG. Clinical predictors of complications and outcomes in degenerative cervical myeloradiculopathy. Indian Spine J 2019;2:59-67
|How to cite this URL:|
Wilson JR, Jiang F, Fehlings MG. Clinical predictors of complications and outcomes in degenerative cervical myeloradiculopathy. Indian Spine J [serial online] 2019 [cited 2019 Mar 24];2:59-67. Available from: http://www.isjonline.com/text.asp?2019/2/1/59/249901
| Introduction|| |
Degenerative cervical myelopathy (DCM) is the leading cause of spinal cord dysfunction worldwide, and it is one of the most common indications for spinal surgery in North America., The term DCM encompasses a group of chronic, atraumatic spinal cord injuries that can occur from static cord compression (i.e., disc spondylosis, ligamentum flavum hypertrophy, and ossification of the posterior longitudinal ligament [OPLL]) or repetitive dynamic injury from hypermobility [Figure 1]. The natural history of DCM is usually one of progressive neurological dysfunctions, and surgical management has been shown to be very effective at arresting deterioration and improving neurological outcomes., Clinical practice guidelines have been produced to provide clear recommendations for the use of appropriate surgical management for DCM patients. Decisions regarding the optimum surgical approach for DCM, however, remain difficult. This is mostly due to the heterogeneous patient cohort and the highly variable etiology of DCM. A number of clinical and surgical factors exist that affect the outcomes from surgical management of DCM patients.,,, For the treating clinician, understanding the relationship between each factor and the overall burden of operative management is paramount in achieving the most optimal outcome for each individual.
|Figure 1: “An artistic depiction of the multiple anatomical changes that may present in the cervical spine of patients with degenerative cervical myelopathy. Conceptual design by primary author, edits by senior author, and medical illustration by Diana Kryski (Kryski Biomedia). PLL: Posterior longitudinal ligament, CSF: Cerebrospinal fluid.” Reprinted with permission from Nouri A, Tetreault L, Singh A, Karadimas SK, Fehlings MG. Degenerative Cervical Myelopathy: Epidemiology, Genetics, and Pathogenesis. Spine. 2015;40 (12):E675-93|
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| Patient Demographics and Comorbidities|| |
A number of clinical predictors have been demonstrated to have an effect on the outcomes of surgical management of DCM, including age, index myelopathy severity, duration of symptoms, smoking status, and the presence of physical/psychological comorbidities [Table 1].
The significance of age on the effect of surgical outcomes for DCM is controversial. Many articles have described nonsignificant differences in outcomes in terms of modified Japanese Orthopaedic Association (mJOA), Nurick, and SF-36 scores when directly compared to standardized, younger patient cohorts.,, However, the burden of evidence would suggest that increasing age is an independent predictor of achieving a poor or fair outcome.,,, Tetreault et al. had consistently shown that older patients are less likely to achieve an mJOA score ≥16 at 1 year or achieve a minimum clinically important difference (MCID) after surgery for DCM based on the analysis of the Cervical Spondylotic Myelopathy (CSM)-North America and CSM-International datasets.,, The same analysis also demonstrated that a higher number or more severe degree of comorbidities (higher comorbidity score) was correlated to an increased likelihood of poor recovery, as was a history of smoking tobacco. Patients who smoked were less likely to achieve an mJOA ≥16 and less likely to achieve the MCID after surgery; however, this seemed less relevant for those with a baseline preoperative mJOA of ≤12. Other groups had shown that tobacco smokers exhibit smaller improvements in the Nurick grade and Neck Disability Index (NDI) after surgery for DCM.,
Patients with significant psychological comorbidities, such as bipolar affective disorder or depression, have also been shown to have worse functional outcomes (SF-36v2 mental component score) after DCM surgery despite equivalent clinical outcomes on the mJOA or Nurick grading compared to groups without psychological comorbidities.
| Baseline Myelopathy Severity and Duration of Symptoms|| |
A number of studies have assessed the relation of baseline severity of myelopathy/duration of myelopathy symptoms with the chances of achieving a functional or satisfactory outcome after DCM surgery. Many studies have been published that describe no significant relationship between the mJOA or JOA recovery rate after surgery and the severity of preoperative myelopathy symptoms.,,,, However, the majority of evidence seems to favor the notion that a worse preoperative myelopathy assessment score (Nurick, mJOA, or JOA) is correlated with a higher risk of “poor” or “fair” recovery rate. Gao et al. presented a retrospective analysis of 145 consecutive patients undergoing surgery for DCM, with a mean follow-up of 5 years. They showed that patients with a baseline JOA of ≤9 were 4.84 times more likely to exhibit a “fair” outcome (<50% recovery rate) when compared to those with a JOA >9. Similar outcomes for recovery rate have been demonstrated with lower preoperative JOA scores in a retrospective series of patients undergoing cervical laminoplasty (LP)., Pumberger et al., together with other groups, also demonstrated on retrospective analysis that patients with less severe myelopathy on the Nurick grading system (≤3) were more likely to achieve a grade of 0, 1, or 2 postoperatively compared to patients with a preoperative grade of ≥4.,, Patients with symptom duration of <12 months were 4.8 times more likely to improve and 14 times more likely to return to a Nurick grade of 0 postsurgery when compared to the group with >12-month duration.
At the other end of the spectrum, patients with a milder severity of myelopathy appear to have a greater chance of achieving a higher JOA/mJOA recovery rate after surgery.,,,,, These findings are reflected in the results our group has published arising from the CSM-North America and CSM-International data; patients are more likely to achieve a postoperative mJOA ≥16 or ≥12 after surgery for DCM if their preoperative baseline mJOA scores were higher., Patients were also more likely to achieve an mJOA of ≥16 or ≥12 if their symptom duration was shorter; the probability of achieving the MCID on the mJOA scale falls by 6% if the patients move from the <3-month group to the 3–6-month group. There is a problem, however, with reporting mJOA/JOA recovery rates alone without considering the objective change in scores from before and after surgery.
Tetreault et al. highlighted this point and explained that, while many studies have been unable to demonstrate a difference in recovery rates with different severities of myelopathy, when the analysis is based on the change in postoperative mJOA scores, then a significant difference is much more prevalent.,,,,, One must, therefore, consider the impact of the MCID when comparing mJOA outcomes after DCM surgery, particularly within the patients in the “mild” group (mJOA ≥15). A recent study from Badhiwala et al. demonstrated that patients with mild DCM represent a heterogeneous group, usually younger in age, with a substantial disease burden when assessed using quality of life scales such as the SF36v2 or SF-6D. Surgery was associated with a dramatic improvement in these measures at 2-year follow-up, sometimes up to four times the MCID (SF-6D), and recent focus has shifted toward developing these tools as a means to guide predictors and outcomes in DCM surgery, rather than traditional assessment scales (such as the mJOA).
| Preoperative Imaging Characteristics|| |
To date, several studies have evaluated the predictive value of imaging features on treatment outcomes in DCM. While the majority of the focus was on the operative group of patients, Shimomura et al. showed that, in individuals with mild DCM treated with nonoperative management, the presence of circumferential compression of the spinal cord on the axial reconstruction of magnetic resonance imaging (MRI) is a predictor for further deterioration. Thus, this raised the question of indications for prophylactic surgery in specific subgroups of patients experiencing mild DCM. While this topic is still controversial in the field of spine surgery and is far beyond the scope of this review, a recent management guideline on DCM published by our group reviewed the most updated evidence in the literature and concluded that both surgical management or nonsurgical management are viable options for patients experiencing mild symptoms, provided close followups are maintained.
The predictors of poor outcomes in the operative group of patients have undergone a thorough investigation. Nouri et al. reported that the presence of T1-weighted hypointensity, combined T1- and T2-weighted signal changes, or greater number of levels of T2-weighted hyperintensity on preoperative MRI, was predictive of poor recovery following operative decompression., Since these imaging findings typically reflect severe cellular damage and cavitation, their presence on MRI implies extensive underlying injury to the spinal cord and suggests the possibility of irreversibility even with the removal of compressive elements.
In addition, the T2-weighted signal change ratio, as calculated by the hyperintense signal at the area of maximal compression compared to the baseline intensity taken from the cerebrospinal fluid or normal spinal cord level, has also been previously shown to predict neurological recovery negatively; however, this association did not reach statistical significance.
Previously, studies by Yamazaki et al. and Nouri et al. investigated the relationship between the extent of spinal cord compression and clinical outcomes., Although the chosen techniques of measurement by both studies were different, both authors were able to identify a relationship between the extent of cord compression and postoperative outcome. While the presence of severe stenosis itself is not a direct MRI feature for irreversible damage, the more severe the compression and the smaller the transverse diameter at the level of maximal compression indirectly suggests a more extensive injury to the spinal cord and association with worse postoperative neurological outcomes.
| Surgical Approach: Anterior Versus Posterior|| |
Aside from the few exceptions where an anterior or posterior approach is heavily favored (i.e., focal cervical kyphosis or long-segment posterior compression), the optimal approach for decompressive surgery in DCM is a strong area of contention worldwide. The mainstay of anterior approaches is cervical discectomy (single or multilevel), or corpectomy, compared to laminectomy/LP with or without instrumented fixation through the posterior approach. It is common to favor the anterior approach in patients with less severe myelopathy, if fewer levels are involved, in the presence of ventral pathology and in younger patients., The evidence for anterior only approaches, however, becomes less convincing in the presence of ≥3 level pathology.,,
In 2013, the results of the multicenter AOSpine North America CSM prospective trial comparing the outcomes in 264 patients using anterior or posterior approaches were published. There was no significant difference in the rates of complications between the groups despite the posterior cohort undergoing a greater number of cervical levels. Postoperative improvement in both groups at 12 months was equivalent with regard to mJOA, Nurick grade, NDI, and SF-36v2 scores. Certain complications were specific to each group (i.e., dysphagia from the anterior approach), but this did not significantly affect the functional outcomes. A more recent study based on 245 patients from the Quality Outcomes Database also presented the outcomes from anterior versus posterior approaches of patients undergoing 3–5-level decompressive surgery for DCM. The results echo those of Kato et al. (anterior approach is favored in younger patients and with fewer levels of pathology), with the addition that 90-day readmission and 12-month reoperation rates were also equivalent between the two groups, as well as the functional outcome scores. The posterior cohort had a significantly longer length of stay (3 days compared to 1 day). This particular result was not replicated in the propensity score-matched analysis of patients from the CSM-North America and CSM-International datasets performed by Kato et al. The authors used a logistic regression model to adjust for confounding bias such as baseline characteristics and MRI appearances. The result was equivalent operative duration, length of stay, rates of complications, and functional outcome scores (mJOA, NDI, and SF36v2) at 2 years.
The current interpretation of the evidence would seem to suggest equivalent outcomes and complication rates for anterior and posterior decompressive surgery for DCM. The CSM-S trial (a prospective, multicenter, randomized controlled trial of anterior versus posterior decompression for DCM) has now completed enrollment, and the results may substantially add to our understanding of the influence of the choice of surgical approach on the functional outcomes of DCM surgery. For now, a view supported by most is that the choice of surgical approach is a decision best left to the experience of the surgical team.,,
| Variations in the Anterior Approach|| |
There are numerous options for anterior surgery for DCM. The most common procedures include anterior cervical discectomy and fusion (ACDF), anterior cervical corpectomy and fusion (ACCF), or a hybrid procedure using a combination of ACDF and ACCF. Cervical arthroplasty (or cervical “artificial disc” [CAD] prosthesis) and oblique corpectomy without fusion have also been described for the surgical treatment of DCM. ACDF is a well-established procedure for ventral decompression of the cord that can be performed safely and effectively at multiple levels, even as outpatient or day-surgery procedures [Figure 2]., ACCF has been well described and provides a method to achieve ventral decompression in the presence of significant retrovertebral pathology., Complications of ACCF include cage subsidence and pseudoarthrosis, and many surgeons will opt to stabilize an ACCF construct with posterior instrumented fixation. Oblique corpectomy without fusion is a procedure to remove the posterior vertebral body to decompress the ventral cord, without removing ≥50% of the body, from a more lateral approach. It negates the necessity for instrumentation, and the proponents have argued that long-term stability on flexion/extension is maintained with similar long-term neurological outcomes compared to conventional ACCF surgery., More recently, the concept of a “hybrid” construct has been established where an ACDF is used superior or inferior to an ACCF to reduce the potential morbidity associated from >2 level corpectomy., To establish the optimal anterior approach for multilevel DCM pathology, Shamji et al. in 2013 performed a systematic review comparing multilevel discectomy versus corpectomy versus hybrid procedures. Based on ten studies used in the final analysis, there was moderate evidence to support an improvement with NDI scores and sagittal alignment with multilevel ACDF over and above ACCF, with moderate evidence to support improvement in JOA scores and sagittal alignment with ACDF over hybrid procedures. Moderate levels of superiority for postoperative JOA scores were found in favor of ACCF over hybrid procedures; however, hybrid procedures showed superiority with NDI scores and sagittal alignment when compared to ACCF alone. All three procedures were found to have equivalent rates of nonunion, dysphagia, and infection.
|Figure 2: An example of multilevel anterior cervical discectomy and plating for degenerative cervical myelopathy. (a) Sagittal T2-weighted magnetic resonance imaging demonstrating multilevel spondylosis leading to cord compression and loss of cervical lordosis. (b) Sagittal computed tomography spine of the same patient. (c) Postoperative lateral X-ray demonstrating return of cervical lordosis and fusion between allograft cages C3–C6. (d) Postoperative magnetic resonance imaging at 1 year demonstrating decompression of the cord across the operated levels|
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The evidence would, therefore, point toward the use of multilevel ACDF over ACCF or hybrid procedures where possible, given the superior surgical outcomes., Comparison of ACCF and hybrid procedures produced conflicting results, and no firm recommendations can be established regarding superiority for one approach over the other. No evidence exists that directly compares outcomes for oblique corpectomy versus traditional ACDF or ACCF.
CAD procedures for the treatment of single or multilevel pathology have become increasingly popular in the last decade, particularly for radiculopathy, but relatively less evidence has been published to support their use in the setting of DCM compared to the other procedures already discussed. Complications specific to CAD include heterotopic ossification, implant subsidence, and loss of motion on follow-up, but the proponents suggested that preservation of motion may reduce the future incidence of adjacent segment disease. Fay et al. in 2014 presented 72 DCM patients treated with CAD. At 3 years, average NDI and mJOA scores were significantly improved, but three patients showed no movement across the prostheses, and heterotopic ossification was seen in 47.2% of patients. Many studies have since shown equivalent outcomes from CAD when compared to ACDF in single or multilevel disease, including prospective nonrandomized studies and randomized control trials.,, Some long-term retrospective cohort studies have suggested that patients undergoing CAD have superior outcomes on the mJOA, Nurick, and NDI/Oswestry Disability Index (ODI) scales, but pooled analysis has not provided a clear superiority of CAD over ACDF, or vice versa., A recent meta-analysis (based on eight studies with a minimum 4-year follow-up) demonstrated a significantly higher same or adjacent level reoperation rate with ACDF (16.8%) when compared to CAD (7.4%). It is clear that many questions remain regarding the long-term outcomes and complication rates of CAD when treating multilevel DCM pathology. The data at present suggests at least equivalent clinical outcomes in the short term compared to traditional ACDF procedures, but certainly, further prospective studies with long-term follow-up are required before any reliable conclusions can be drawn.
| Variations in the Posterior Approach|| |
Posterior approaches for DCM surgery in the current age usually consist of laminoplasty (LP) or laminectomy with instrumented fusion (LF) [Figure 3]. LP aims to maintain segmental stability by maintaining the bony posterior elements with ligamentous attachments and arose in the 1970s as a solution to the well-documented unacceptably high rates (~20%) of pathological kyphosis after cervical laminectomy., The development of posterior instrumented fixation techniques has seen long-segment LF become a safe and effective management option for multisegment DCM without kyphosis. Many cohort studies have reported improved neurological outcomes in mJOA, Nurick grading, or NDI/ODI/VAS scores using the LF posterior approach with long-term follow-up.,,, Fehlings et al. in 2017 presented the results from a prospective cohort of 266 patients directly comparing the outcomes of patients with LF (n = 166) to those undergoing LP alone (n = 100). Patients undergoing LF procedures demonstrated significant improvements at 24 months in Nurick grade, mJOA, NDI, and SF36v2 compared to preoperative scores. After adjusting for baseline characteristics, the patients undergoing LP had similar improvements in all outcome measures with no significant differences. LF patients had shorter hospital stays (7.8 vs. 11.6 days), but both cohorts had equivalent rates of shared complications and reoperation. Another study by Highsmith et al. (using retrospective cohorts) reported significant improvements in postoperative neck pain in the LF group and similar improvements in neurological outcomes in both groups, but reported a complication rate requiring reoperation twice as high (27% vs. 13%) in the LF group compared to the LP group. In addition, implant costs were much larger in the LF group.
|Figure 3: An example of multilevel posterior decompression and instrumented fixation. (a) Sagittal T2-weighted magnetic resonance imaging demonstrating a combination of multilevel spondylosis and degenerative listhesis causing cord compression from C3–C7. (b) Sagittal computed tomography spine demonstrating significant vertebral body sclerosis and osteophytic changes. (c) Postoperative lateral X-ray demonstrating instrumented fixation from C2 to T1. (d) Sagittal magnetic resonance imaging at 1 year postoperatively demonstrating decompression from C3–C7 and restoration of canal diameter|
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Attempts at combining cohort studies comparing LF and LP outcomes have proved difficult; however, Yoon et al. presented a systematic review that included four studies to assess superiority of clinical outcomes. Three of the four studies assessing myelopathy severity found no significant difference between the LF or LP groups. Rates of reoperation or other neurological complications were variable between groups across all four studies, and the authors' conclusions were that no definitive evidence exists that demonstrates superiority of either procedure. Similar conclusions were presented in a systematic review by Lee et al. in 2015 in terms of clinical outcomes; however, the LF group seemed to have better preservation of cervical lordosis on radiological follow-up compared to the LP group. Overall, it appears that LF and LP are both safe and effective at producing postoperative improvement in myelopathy outcome measures, with no evidence at present to suggest one method is superior to the other. LF appears to be more effective at reducing neck pain and preserving long-term lordosis. However, the decision to opt for LF or LP has a wide geographical variation, and patient factors (such as the presence of OPLL) will affect the choice of procedure greatly. Further studies are therefore required if the question of superiority of LF versus LP is to be more definitively addressed.
| Restoration of Sagittal Alignment|| |
It has been suggested that the sagittal alignment of the cervical spine plays a vital role in the development and progression of DCM. Thus, any spinal deformity associated with DCM will need to be considered at the stage of operative planning. Previous research has identified the presence of large OPLL and preoperative cervical kyphosis as predictors of poor outcomes following LP for DCM.,, These studies highlighted the importance of global sagittal alignment and the inadequacy of posterior decompression alone in the setting of severe cervical kyphosis. On account of this, the concept of K-line was first introduced as a decision tool to predict the likelihood of successful decompression with the posterior alone procedure. Later, the K-line was modified for application on MRI sagittal image to improve the accuracy and to further introduce the concept of minimum interval distance (INT)., The modified K-line extends from a point at the mid-cord level of C2 to the same mid-cord point at the level of C7; the distance between the line and the anterior compressive elements is considered the INT [Figure 4]. The same group has established the relationship between INT and poor clinical outcomes, and they further demonstrated that an INT <4 mm in the presence of cervical kyphosis is associated with increased risk of postsurgical residual cord compression.,
|Figure 4: An example of a modified K-line superimposed on a mid-sagittal T2-weighted imaging in two patients with degenerative cervical myelopathy. The line is drawn from the mid-cord at the midpoint of C2 and extends to the mid-cord level of the midpoint of C7. Patient A has a significant loss of cervical lordosis and the anterior border of the canal encroaches on the modified K-line (a), which is in stark contrast to Patient B who has maintained cervical lordosis (b). This would suggest different surgical approaches are required for each patient to avoid residual cord compression after surgery|
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While it is known that neurological recovery is less pronounced in patients with preoperative cervical kyphotic alignment, evidence suggests that these patients demonstrate more significant improvement with an anterior or combined anterior/posterior approach. Similarly, Uchida et al. confirmed the importance of sagittal deformity correction, showing the benefit of alignment restoration in maximizing the potential for clinical improvement in patients with preoperative cervical kyphosis ≥10°. Therefore, when considering the operative management of patients with DCM, careful consideration of global sagittal alignment during operative planning is imperative for the success.
| Conclusion|| |
Many factors have been demonstrated to affect the outcomes and complications in surgery for DCM. Clinical factors such as age, severity of myelopathy, duration of myelopathic symptoms, and the presence of comorbidities have important roles in predicting the neurological outcomes and complications after DCM surgery. In addition, surgical factors such as the choice of anterior or posterior approach, the presence of radiological changes, and postoperative restoration of sagittal alignment can have great effects in the outcomes from DCM surgery. Given the wide heterogeneity in the symptomology and pathophysiology of DCM patients, the surgical team must have a comprehensive knowledge of how these factors affect each other and can influence the outcomes for each patient. This enables more realistic management of patient expectations and helps reduce the rates of reoperation and complications in the long term.
Dr. Jamie Wilson is kindly supported by the Dowager Countess Eleanor Peel Charitable Trust.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]