Quality assessment of systematic reviews of surgical treatment of cervical spine degenerative diseases: an overview

ABSTRACT

Objective

To gather all systematic reviews of surgical treatment of degenerative cervical diseases and assess their quality, conclusions and outcomes.

Methods

A literature search for systematic reviews of surgical treatment of degenerative cervical diseases was conducted. Studies should have at least one surgical procedure as an intervention. Included studies were assessed for quality through Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) and Assessment of Multiple Systematic Reviews (AMSTAR) questionnaires. Quality of studies was rated accordingly to their final score as very poor (<30%), poor (30%-50%), fair (50%-70%), good (70%-90%), and excellent (>90%). If an article reported a conclusion addressing its primary objective with supportive statistical evidence for it, they were deemed to have an evidence-based conclusion.

Results

A total of 65 systematic reviews were included. According to AMSTAR and PRISMA, 1.5% to 6.2% of studies were rated as excellent, while good studies counted for 21.5% to 47.7%. According to AMSTAR, most studies were of fair quality (46.2%), and 6.2% of very poor quality. Mean PRISMA score was 70.2%, meaning studies of good quality. For both tools, performing a meta-analysis significantly increased studies scores and quality. Cervical spondylosis studies reached highest scores among diseases analyzed. Authors stated conclusions for interventions compared in 70.7% of studies, and only two of them were not supported by statistical evidence.

Conclusion

Systematic reviews of surgical treatment of cervical degenerative diseases present “fair” to “good” quality in their majority, and most of the reported conclusions are supported by statistical evidence. Including a meta-analysis significantly increases the quality of a systematic review.

Spinal diseases; Cervical vertebrae; Chronic disease; Hernia; Intervertebral disc; Spondylosis; Orthopedic procedures

INTRODUCTION

Neck pain is a common complaint in primary care and orthopedic settings, and is often related to cervical spine conditions. Neck pain is currently the fourth leading cause for workman’s compensation claims and functional impairment in the United States.(¹) Every year the cost of treatment increases, especially when surgical intervention for degenerative cervical disease is involved.(²,³) Common causes for surgical intervention in the cervical spine are cervical stenosis, myelopathy, spondylosis, degenerative disc disease, and facet joint arthritis.

Although conservative treatment is the primary choice of treatment for degenerative conditions of the cervical spine in the absence of neurological impairment, severity and duration of symptoms can lead the patient and provider down the path of surgical intervention. As new surgical techniques and implants are developed, scientific evidence seems to be lacking for most surgical indications. Theoretically, systematic reviews of randomized clinical trials (RCT) are on the top of the pyramid of scientific evidence, and are the source of decision-making for most spine surgeons when conducting their clinical algorithm.

However, there appears to be a substantial mismatch between the results of systematic reviews in spine surgery and daily practice outcomes. Recently, Martins et al.,(⁴) published an overview of systematic reviews for surgical treatment of low back pain (LBP), and reported most reviews lack methodological quality and frequently state conclusions not based on statistical evidence. Authors often suggest their evidence is underpowered by the lack of clinical trials, and criticize that the ones available present methodological flaws.

OBJECTIVE

To assess the quality of all published systematic reviews for surgical treatment of degenerative disease of the cervical spine, as well as analyze if the results of each study are supported by their methodologies.

METHODS

Study design

This is an overview of systematic reviews.

Study eligibility criteria

All systematic reviews available in the queried databases containing at least one surgical treatment for any cervical spine degenerative disease as an intervention were included. Both open and minimally invasive techniques were considered. Systematic reviews comparing non-surgical treatment strategies were excluded, as well as those involving thoracic or lumbar degenerative diseases. Included studies were categorized by conditions, such as cervical disc herniation (CDH), degenerative disc disease, cervical stenosis/myelopathy, and spondylosis. Spinal injections were not considered as a surgical intervention.

Data extraction and study quality assessment

Six reviewers independently used a standardized form to extract data. Descriptive analysis, such as journal and date of publication, cervical disease studied, surgical intervention, conflict of interests, funding, number of included studies, primary and secondary outcomes, statistics, meta-analyses, and conclusions were assessed for each study. All reviewers assessed the quality of included studies with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA),(⁵) and Assessment of Multiple Systematic Reviews (AMSTAR)(⁶) tools. Both tools are validated measurement questionnaires that assess the methodological quality of systematic reviews. PRISMA is divided into domains that were also independently analyzed (title, abstract, introduction, methods, results, discussion and funding). According to a previously published article by this same group of researches,(⁴) we classified each PRISMA item as yes, incomplete, or no, and respectively scored as 1, 0.5, or 0 points for statistical analysis purposes. Similarly, the AMSTAR tool had each item graded as yes or no and scored as 1 or 0, respectively. All reviewers were primarily trained for each item of both questionnaires and an inter- as well as intraobserver correlation reliability was assessed for both PRISMA and AMSTAR tools, through a Kappa concordance coefficient for separate items and intraclass correlation coefficient for total scores. For PRISMA, the intraclass correlation coefficient was 0.966 (95% confidence interval – 95%CI 0.889-0.990, p<0.001), which is considered very good according to Landis et al.(⁷) For AMSTAR, an intraclass correlation coefficient of 0.912 (95%CI 0.734-0.973, p<0.001) was achieved, also considered a very good concordance. Any disagreement that might have arisen was discussed and resolved by consensus, and with an opinion of a seventh reviewer with expertise in systematic reviews. The sum of all items scored for each questionnaire was divided by its maximum possible score, to evaluate study quality as a percentage.(⁴) Systematic reviews were classified according to AMSTAR and PRISMA percentages as follows: very poor (<30%), poor (30%-50%), fair (50%-70%), good (70%-90%), and excellent (>90%).(⁴) We collected the following items for every systematic review: year of publication; disease, intervention, and study control; evidence-based primary outcomes through reported statistics; and outcomes reported.

Analysis of outcomes, interventions, and diseases

We extracted data for each included study for population, intervention, control, and outcomes (PICO). Population was grouped according to the disease investigated (CDH, myelopathy, spondylosis, degenerative disc disease) and compared. Interventions and outcomes were also grouped accordingly. Two authors independently reviewed every included article to analyze the validity of the conclusion reported. We considered conclusive studies those with a valid conclusion addressing the primary outcome. If an article reported a conclusion addressing its primary objective, we searched the article for supportive statistical evidence for the conclusion. Articles meeting this criterion were deemed to have an evidence-based conclusion.

Search strategy

After institutional review board approval (# 2742), we conducted a literature search for systematic reviews that employed at least a single surgical treatment method of degenerative cervical spine disease, through available medical databases: MEDLINE (PubMed), EMBASE (Ovid), Cochrane Database of Systematic Reviews, and the Database of Abstracts of Reviews of Effectiveness. There was no restriction to language or date. Appendix 1 demonstrates the search strategy used for MEDLINE. For other databases, we followed the same search strategy with minimal adjustments. Two investigators independently assessed all titles and abstracts to exclude duplicate articles and selected articles with potential to be included. When any disagreement was raised, a third author was consulted to solve inconsistencies. Studies from the same research group with similar intervention and analyses had only the most recent version included.

Appendix 1
Search strategy for MEDLINE

a

((((Zygapophyseal Joint [mh] OR Neck Pain [mh] OR cervical pain [mh] OR neck pain [tw] OR facet joint* [tw] OR cervical pain [tw] OR Intervertebral disk degeneration [mh] OR spinal stenosis [mh] OR cervical myelopathy [tw] OR myelopathy [mh] OR hernia* [tw] OR prolapse* [tw] OR extru* [tw]))) AND (((neck surgery [tw] OR Spinal fusion [mh] OR Arthrodesis [mh] OR Laminectomy [mh] Instrumentation [tw] OR Decompression, Surgical [mh] OR fusion [tw] OR in situ fusion [tw] OR interbody fusion [tw] OR disc replacement [tw] OR arthroplasty [tw])))) AND ((meta-analysis [pt] OR Systematic Reviews [tw] OR randomized controlled trial [pt] OR controlled clinical trial [pt] OR randomized controlled trials [mh] OR random allocation [mh] OR double-blind method [mh] OR single-blind method [mh] OR clinical trial [pt] OR clinical trials [mh]))

Statistical analysis

Statistical analysis consisted of descriptive statistics including relative and absolute frequencies. Inter-observer concordance of the AMSTAR and PRISMA scores was assessed through the Gwet AC1 coeficient.(⁸) Numerical variables were reported as medians, quartiles, boxplots and histograms. Group comparison was performed through a Mann-Whitney test for numerical variables, while categorical variables were compared through Fisher´s exact test. A Holm test was used for post-test correction. For all tests, a p value of 0.05 was considered significant. Statistics were performed with the software R 3.4.1 (R Foundation for Statistical Computing, Vienna, Austria).

RESULTS

After a full electronic search, we identified a total of 2,996 references (Figure 1). After title, abstract and duplicate screening, we excluded 2,480 references and 71 articles were fully assessed for eligibility. Six studies were excluded (Figure 1)(⁹-¹⁴) and 65 were included for qualitative analysis.(¹⁵-⁷⁹) All 65 studies were written in English, and included at least one surgical procedure to treat cervical spine degenerative disease.

Figure 1
Flowchart of included articles

Descriptive analysis

More than half (56.9%) of included systematic reviews of surgical treatment of cervical degenerative diseases were published within the last four years,(¹⁵-¹⁸,²⁰-²⁶,²⁹,³¹,³⁵-⁴¹,⁴³,⁴⁵-⁴⁸,⁵⁰,⁵³,⁵⁷,⁵⁸,⁶⁰,⁶²,⁶³,⁶⁵-⁶⁹,⁷³-⁷⁵,⁷⁷) with the rest ranging from 1999 to 2016. The most studied disease state was myelopathy due to degenerative compression of the spinal cord, accounting 41.5% of included studies,(¹⁵,¹⁶,¹⁸,²⁰-²²,²⁵,²⁶,²⁸,³¹,³⁶,³⁸,⁴¹,⁴²,⁴⁴,⁴⁷,⁴⁸,⁵²,⁵³,⁵⁸,⁶⁸-⁷⁰,⁷²,⁷⁴,⁷⁷) followed by degenerative disc disease (33.8%),(¹⁹,²³, ²⁴,²⁷, ³⁰,³²,³⁹,⁴⁰,⁴³,⁴⁵,⁴⁹-⁵¹,⁵⁷,⁵⁹-⁶²,⁶⁴,⁷³,⁷⁵,⁷⁸) spondylosis (13.8%)(³⁶,³⁸, ⁴⁷,⁵⁷,⁶⁴,⁶⁶,⁶⁸,⁷²,⁷⁷) and CDH (9.2%).(¹⁸,³⁴,³⁵,⁵⁵,⁵⁶,⁶⁷) There was one study that analyzed adjacent segment degeneration,(¹⁵) and was not included in the pre-established groups. The surgical interventions that were most frequently analyzed were anterior cervical discectomy and fusion (ACDF) (72.3%),(¹⁹,²¹,²⁵,²⁷,³⁰-³⁴,⁴⁰,⁴¹,⁴⁴,⁴⁵,⁴⁹,⁵¹,⁵²,⁵⁴,⁵⁶,⁵⁹,⁶⁰,⁶²-⁶⁹,⁷¹,⁷²,⁷⁴,⁷⁸) followed by total disc replacement (TDR) (44.6%).(¹⁷,¹⁹,²³-²⁵,³⁰,³⁹,⁴⁰,⁴³,⁴⁵,⁴⁶,⁴⁹,⁵¹,⁵⁴,⁵⁵,⁵⁷,⁵⁹-⁶⁵,⁶⁷,⁶⁸,⁷¹,⁷⁵,⁷⁶) The comparison of ACDF versus TDR was considered in 27 studies (41.5%).(¹⁹,²¹,²⁵,²⁷,³¹-³³,⁴⁰,⁴⁵,⁴⁹,⁵¹,⁵²,⁵⁴,⁵⁶,⁵⁹,⁶⁰,⁶²,⁶⁴-⁶⁹,⁷¹,⁷²,⁷⁴,⁷⁸) The third most studied intervention was laminoplasty, present in 20% of included studies.(¹⁶,¹⁷,¹⁹, ²³,²⁷,²⁹,³²,⁴⁹,⁷³,⁷⁵)

Most systematic reviews performed a meta-analysis (86.2%) and demonstrated statistical significance for comparison of primary outcomes in 67.7% of all included studies. Authors stated conclusions for interventions compared in 70.7% of studies. This means that two studies stated a conclusion on primary outcomes not based on statistical evidence, denoting an inconsistent conclusion.(²⁵,²⁷) The majority of studies (56.9%) had a funding source declared other than authors own expenses, while 9.2% did not mention funding source. Potential conflicts of interest were detected in 30.8% of studies.(¹⁵,²³,²⁴,²⁶,²⁸,³⁶,³⁸,³⁹,⁴¹,⁴⁵,⁴⁷,⁵²,⁵³,⁵⁷,⁶⁰,⁶³,⁶⁴,⁶⁸,⁷⁸,⁷⁹) Having or not conflicts of interest or funding declared did not influence final mean AMSTAR score (58.5% with funding versus 58.7% without funding; 58.6% with conflicts of interest versus 58.6% without conflicts). Out of the 20 articles declaring conflicts of interest, 9 analyzed TDR and 5 laminoplasty. Furthermore, 65% of those with declared conflicts of interests described methods used for assessing risk of bias, against 53.6% of those without conflicts. We compared final PRISMA and AMSTAR scores between studies with meta-analysis and those without a meta-analysis. Systematic reviews performing a meta-analysis presented significantly higher scores for both questionnaires, compared to those without (Figure 2).

Figure 2
Assessment of multiple systematic reviews and Preferred Reporting Items for Systematic Reviews and Meta-Analyses percentage scores distribution, according to performing or not a meta-analysis. n=65

The most common outcome used for surgical treatment of degenerative cervical diseases was the visual analog scale (VAS), which was present in 60% of articles, followed by the Japanese Orthopaedic Society questionnaire (JOA) and neck scale, present in 44.6% and 43.1%, respectively.

Descriptive study quality analysis

Final percentages scored for PRISMA (total and domains) and AMSTAR are shown in table 1. Individual AMSTAR scores for each article included are shown in table 2.

Table 1
AMSTAR and PRISMA domains by percentage of final score

Quality tool	Mean score (%)
AMSTAR total	58.2
PRISMA total	70.2
PRISMA - Title	87.7
PRISMA - Abstract	54
PRISMA - Introduction	75
PRISMA - Methods	65
PRISMA - Results	70
PRISMA - Discussion	88.9
PRISMA - Funding	67.7

• PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Table 2
Individual AMSTAR scores for each item (first row) of each article (first column). Total checked results are presented in percentage (last column) and checked items are presented as “X”

Authors	1	2	3	4	5	6	7	8	9	10	11	Total (%)
Boselie et al.,(61)		X	X	X	X	X	X	X	X	X	X	90.91
Zhong et al.,(63)		X	X	X		X	X	X	X	X	X	81.82
Bartels et al.,(18)	X	X	X	X		X	X	X	X		X	81.82
Li et al.,(77)	X	X	X			X	X	X	X	X	X	81.82
Dong et al.,(38)	X	X	X	X		X	X	X	X		X	81.82
Liu et al.,(16)		X	X	X		X	X	X	X	X	X	81.82
Luo et al.,(34)	X	X	X			X	X	X	X		X	72.73
Liu et al.,(32)		X	X			X	X	X	X	X	X	72.73
Wu et al.,(62)	X	X	X			X	X	X	X		X	72.73
Guan et al.,(37)		X	X			X	X	X	X	X	X	72.73
Lu et al.,(60)		X	X			X	X	X	X	X	X	72.73
Jacobs et al.,(51)		X	X	X		X	X	X	X		X	72.73
Botelho et al.,(26)		X	X		X	X	X	X	X		X	72.73
Verhagen et al.,(20)		X	X			X	X	X	X	X	X	72.73
Gu et al.,(49)	X	X	X			X	X	X	X		X	72.73
Han et al.,(45)	X	X	X			X	X	X	X			63.64
Rao et al.,(64)		X	X				X	X	X	X	X	63.64
Yin et al.,(50)		X	X				X	X	X	X	X	63.64
Zhang et al.,(33)		X	X				X	X	X	X	X	63.64
Zhang et al.,(58)		X	X			X	X	X	X		X	63.64
Hu et al.,(66)		X	X		X	X	X	X	X			63.64
Gao et al.,(52)		X			X	X	X		X	X	X	63.64
Xiao et al.,(70)		X	X			X	X	X	X		X	63.64
Luo et al.,(43)	X		X			X	X	X	X		X	63.64
Liu et al.,(30)	X		X	X			X	X	X		X	63.64
Lee et al.,(53)		X	X				X	X	X	X	X	63.64
van Middelkoop et al.,(79)		X	X				X	X	X	X	X	63.64
Wang et al.,(73)		X	X			X	X	X	X		X	63.64
Wang et al.,(29)	X	X	X				X	X	X		X	63.64
Verma et al.,(69)	X	X	X				X	X	X		X	63.64
Gao et al.,(24)	X	X	X				X	X	X		X	63.64
Liu et al.,(48)		X	X				X	X	X	X	X	63.64
Fei et al.,(22)		X	X				X	X	X	X	X	63.64
Shamji et al.,(21)		X	X			X	X	X	X	X		63.64
Yuan et al.,(19)	X	X	X			X	X	X	X			63.64
van Middelkoop et al.,(57)		X	X				X	X	X	X	X	63.64
Wang et al.,(71)	X	X	X				X	X	X	X		63.64
Yang et al.,(68)	X	X	X				X	X	X			54.55
Li et al.,(74)		X	X			X		X	X		X	54.55
Tian et al.,(40)		X	X	X			X	X	X			54.55
Aragones et al.,(56)	X		X			X	X	X	X			54.55
Fouyas et al.,(36)	X	X	X						X	X	X	54.55
Harrod et al.,(25)	X		X				X	X	X		X	54.55
Liu et al.,(23)		X	X	X		X	X	X				54.55
Wen et al.,(78)		X	X				X	X	X	X		54.55
Liu et al.,(75)		X	X				X	X	X			45.45
Muheremu et al.,(72)		X	X					X	X		X	45.45
Yu et al.,(55)			X				X	X	X	X		45.45
Xing et al.(76)				X		X			X	X	X	45.45
Fallah et al.,(47)	X		X				X	X	X			45.45
Zhu et al.,(39)		X	X					X	X		X	45.45
Cepoiu-Martin et al.,(46)		X	X			X	X	X				45.45
Jiang et al.,(44)	X	X	X				X		X			45.45
Ren et al.,(65)		X	X						X	X	X	45.45
Zhao et al.,(41)		X	X				X	X	X			45.45
Sun et al.,(54)		X	X						X	X	X	45.45
Lu et al.,(60)		X	X				X	X		X		45.45
Huang et al.,(42)						X	X	X	X			36.36
Shriver et al.,(31)		X				X	X		X			36.36
van Limbeek et al.,(28)		X	X				X	X				36.36
Yoon et al.,(17)			X	X	X	X						36.36
Gebremariam et al.,(67)		X					X	X				27.27
Lao et al.,(27)		X				X					X	27.27
Carrier et al.,(15)		X				X					X	27.27
Molinari et al.,(35)						X		X				18.18
Mean (%)	30.7	84.6	87.7	16.9	7.7	53.8	83	84.6	86.1	40	64.6	58.2

Mean total percentage for all included systematic reviews according to PRISMA was 70.2% (range 37-98.2%), demonstrating studies averaged good quality. Mean total percentage according to AMSTAR was 58.2% (range 18.2-90.9%), showing these were reviews of fair quality. Preferred Reporting Items for Systematic Reviews and Meta-Analyses domains showed variable mean scoring from 54% (abstract) up to 88.9% (discussion). Most flaws were found in the abstract (54%), methods (65%), and funding statement (67.7%), while best rates were in the discussion (88.9%), title (87.7%), and introduction (75%). Results were “good” in 70% of studies.

The items with most flaws in the PRISMA checklist were reporting risk of bias across studies and description of additional analyses, which were reported in only 32.3% and 38.5% of studies, respectively. According to AMSTAR, most reporting flaws were in providing a list of studies (included and excluded), and the item “was the status of publication used as an inclusion criterion?”.

According to PRISMA, the majority (53.9%) of studies supporting surgical treatment of degenerative cervical diseases are rated as having a “good or excellent” quality. There were no studies rated as “very poor” quality (Table 3).

Table 3
AMSTAR and PRISMA quality distribution by percentage of final score

Quality tool	Categories
	Very poor (%)	Poor (%)	Fair (%)	Good (%)	Excellent (%)
AMSTAR	6.2	24.6	46.2	21.5	1.5
PRISMA	0	10.8	35.4	47.7	6.2

• AMSTAR: Assessment of multiple systematic reviews; PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Assessment of multiple systematic reviews had more reviews rated as “fair” (46.2%), and fewer rated as “excellent” and “good” (1.5% and 21.5%, respectively). There was a considerable amount of “very poor quality” reviews (Table 2).

Quality analysis according to disease studied

When reviews were grouped according to the disease studied, the percentage of “good” or “excellent” studies considering PRISMA was higher for spondylosis studies, achieving all nine reviews for this disease (100%),(³⁶,³⁸,⁴⁷,⁵⁷,⁶⁴,⁶⁶,⁶⁸,⁷²,⁷⁷) followed by studies of myelopathy (51.8%) and degenerative disc disease (50%). The AMSTAR tool resulted in smaller percentages of “good” or “excellent” studies, with the highest being CDH (33.3%), followed by degenerative disc disease (22.7%), myelopathy (22.2%) and spondylosis (22.2%) (Table 4).

Table 4
Systematic reviews quality according to the disease studied

Disease population	n	PRISMA >70% n (%)	AMSTAR >70% n (%)	PRISMA and AMSTAR >70% n (%)
CDH	6	1 (16.7)	2 (33.3)	1 (16.7)
Myelopathy	27	14 (51.8)	6 (22.2)	2 (7.4)
Spondylosis	9	9 (100)	2 (22.2)	2 (22.2)
DDD	22	11 (50)	5 (22.7)	5 (22.7)
ASD	1	0	0	0
p value		p=0.006	p=0.692	p=0.689

• n=65. CDH: cervical disc herniation; DDD: degenerative disc disease; ASD: adjacent segment degeneration.

Agreement between AMSTAR and PRISMA

In general, PRISMA scores were higher than AMSTAR. Median difference between both tools was -10.44, although differences were randomly distributed, indicating absence of bias (Figure 3). As AMSTAR scores increase, PRISMA also rises, demonstrating concordance between both tools (intraclass correlation coefficient (ICC) 3 = 0.6, p<0.001).

Figure 3
Agreement between AMSTAR and PRISMA tools according to their percentage scores. n=65

DISCUSSION

On the top of the pyramid of evidence stands systematic reviews, but frequently they do not support our decisions as they often lack quality or fail in their methodology.(⁴) Assessment of Multiple Systematic Reviews and PRISMA are both validated checklists, which guide the production of systematic reviews. While AMSTAR focus on methodological aspects of the research, PRISMA is a more complete checklist involving all the written presentation of the published article. Although our scoring system weights the same numerical point for items inside different domains of PRISMA, such as title or methods, the weights are leveled at the total score, since there are 12 items for methods and only one for title for instance. Thus, the importance of a good-reported methodology is much higher than the paper title itself. It is expected that PRISMA reach higher scores than AMSTAR in our comparison, since there are additional items not related to the methodology of the review that are usually checked, such as those in the title and discussion domains.

In January 2016, our Study Group reported on a low rate of “good” or “excellent” quality systematic reviews for surgical treatment of LBP.(⁴) In this study we found almost double the number of articles for cervical disease as compared to those for LBP. This is most likely because surgical treatment of cervical degenerative diseases is more standardized and less controversial than for LBP. Sixty percent of studies we reviewed for this paper were written within the last four years, while the rate was 50% for LBP. The oldest study included in the lumbar spine review was from 1992.(⁸⁰) The more recent systematic reviews usually follow standardized patterns and protocols before they are performed, such as Cochrane and PRISMA itself. This leads to strictly performed systematic reviews and increases methodological quality, although inclusion of selected RCTs is more exclusive, and frequently systematic reviews will not perform a meta-analysis. This might be one of the reasons we found more “good” or “excellent” articles (53.9% according to PRISMA and 25% for the LBP study)(⁴) in the cervical spine study.

One of the developing technologies in cervical spine surgery is TDR. Much of them were performed by the need to introduce an alternate option to ACDF, and industry funding was an important resource. Funding was declared for 57% of reviews, and we identified a possible conflict of interest between authors and sponsoring industry in 30.8% of them. Sometimes conflicts of interest are disclosed to journal editors, but authors fail to report it within the manuscript will lead to lower AMSTAR and PRISMA scores, and readers might question bias. The interest in introducing a new technique is mostly originated by the implant companies, and comparison is mostly made with what is considered the gold standard. Total disc replacement was compared to ACDF in 27 (41.5%) reviews,(¹⁹,²¹,²⁵,²⁷,³¹-³³,⁴⁰,⁴⁵,⁴⁹,⁵¹,⁵²,⁵⁴,⁵⁶,⁵⁹,⁶⁰,⁶²,⁶⁴-⁶⁹,⁷¹,⁷²,⁷⁴,⁷⁸) and 12 of them concluded that TDR is superior to ACDF.(²¹,³¹,⁴⁰,⁴⁹,⁵⁴,⁶⁰,⁶²,⁶⁵-⁶⁹) Eleven stated that there is no superiority between both techniques,(¹⁹,²⁷,⁴⁵,⁵¹,⁵²,⁵⁹,⁶⁴,⁷¹,⁷²,⁷⁴,⁷⁸)while two reviews did not state a conclusion due to lack of studies.(²⁵,²⁶) One review did not recommend TDR due to its high cost, and lack of proved superiority compared to ACDF.(¹⁸) Only one study concluded that ACDF is superior to TDR for surgical parameters, such as shorter duration of surgery and less blood loss.(⁵²) An interesting fact that demonstrates how time, surgeon learning curve, technique accessibility, and development of good quality clinical trials, is that out of the 15 systematic reviews comparing ACDF and TDR published before 2014, only two reported a superiority of TDR, while 10 out of 12 studies published after 2014 favored TDR. Probably the publication of better clinical trials involving ACDF and TDR changed the results of most systematic reviews. Still, it is a highly controversial topic and theme of discussion in most spine surgery meetings. Theoretically, similar systematic reviews performed within the same period of time should present similar results, although we identified different conclusions. This increases the suspicion that not all reviews have the same quality, and methodology should always be double-checked. In a recent publication of quality analysis of systematic reviews comparing ACDF and TDR using only AMSTAR,(⁸¹) 33.3% of reviews were considered low-quality reviews (AMSTAR <5).

Another source of debate in cervical spine surgery is posterior decompression of the spinal canal. Laminectomy versus laminoplasty are the most compared surgeries for cervical myelopathy in the Asia Pacific region. Laminectomy is usually the treatment choice in the United States and Europe, since the majority of spine surgeons do not perform laminoplasty. This debate is easily demonstrated, since all six systematic reviews included comparing ACDF versus TDR demonstrated no superiority of one technique over the other.(¹⁷,²⁷,²⁹,³²,⁴⁹,⁵³) All those six reviews were published after 2013, demonstrating recent data.

In general, the included systematic reviews completed 70.2% of the 27 items from PRISMA and 58.2% from AMSTAR, which resulted in good quality reviews according to PRISMA, and fair according to AMSTAR. From another point of view, 53.9% of systematic reviews for surgical treatment of the degenerative cervical spine were rated as “good” or “excellent” studies, while this number decreases to 23% according to AMSTAR. Although rating was different, statistical analysis demonstrated correlation between both quality tools. The reviews for cervical degenerative disease were significantly better than those for surgical treatment of LBP, that presented 25% and 32.5% of “good” or “excellent” quality studies according to PRISMA and AMSTAR, respectively.(⁴) As stated before, this should be related to more recent reviews performed following standard protocols, and a higher number of good quality trials available in the literature.

One of the most surprising results was a high rate of conclusions supported by statistical evidence, not only by authors’ own impression. Thus, 67.7% of reviews that presented a conclusion for their primary objective were supported by demonstrated statistics, and only two papers concluded their hypotheses without support.(²³,⁶⁸) On the other hand, only 27.5% of conclusions of the lumbar spine systematic reviews quality-study were supported by evidence.(⁴)

There are some strengths and limitations to our overview. One of the limitations is that we did not access quality of included RCT for each systematic review, which leave us with quality of the systematic reviews and not strength of recommendations, although this was not the aim of this overview. We did not contact the authors of the studies included to clarify inconsistent aspects in their reports. The high number of articles included lengthened the study period and new systematic reviews may have been published during it. The PRISMA tool itself has some items that are not essential for a correct methodology, such as the item regarding “description of additional analysis”, which is optional and not necessary. Scoring this item or not changes the result of the final score and quality of the article, although only few included systematic review performed additional analysis. On the other hand, we ran statistical correlation test to validate every author, when analyzing each systematic reviews for AMSTAR and PRISMA, and this same group of authors have previous experience with this type of assessment, as published in a similar previous overview. We searched for systematic reviews in every main database and found a significant number of included systematic reviews. Also, this is the first assessment of quality systematic reviews for surgical treatment of degenerative cervical diseases using validated tools published as far as we know.

Concerning future recommendations based on our results, we obligate the essentiality of standard guidelines, such as Cochrane Collaboration,(⁸²) to be followed before performing a systematic review or meta-analysis. The same tools used for quality assessment in this research are recommended as guidelines to perform a good quality review, such as the PRISMA statement. An overall impression due to weak results of a substantial number of systematic reviews for surgical treatment is that we still lack good clinical trials to evidence most of our surgical practice, and research teams should spend more time and energy performing trials than systematic reviews that lacks such data. On the other hand, we understand that clinical trials involving surgery are cumbersome, costly, take a long period of time and follow-up, and present numerous bias that frequently turns them unfeasible or weak. Furthermore, the primary interest of the industry is to study innovative interventions rather than repeating previous studies, even if such previous trials are of doubtful quality. Still, a significant funding for surgical trials and research is still coming from the industry, and its interest is most often conflicting.

Researchers investing their time in systematic reviews should optimize their studies into network systematic reviews that are updated regularly, ideally revised with additional new evidence included every 2 to 5 years. This would save time of doing unnecessary repeated search and analysis work. Therefore, authors suggest that readers should analyze cautiously strength of every review based on their methodology and included studies, since two good quality papers comparing same interventions may present opposing recommendations.

CONCLUSION

Systematic reviews of surgical treatment of cervical degenerative diseases present “fair” to “good” quality in their majority, and most of the reported conclusions are supported by statistical evidence. Methodologies of studies reached average “fair” quality according to both tools. Including a meta-analysis significantly increases the quality of a systematic review.

REFERENCES

• ¹
  Yang H, Haldeman S, Nakata A, Choi B, Delp L, Baker D. Work-related risk factors for neck pain in the US working population. Spine (Phila Pa 1976). 2015;40(3):184-92.
• ²
  Cohen SP. Epidemiology, diagnosis, and treatment of neck pain. Mayo Clin Proc. 2015;90(2):284-99. Review.
• ³
  Hoy DG, Protani M, De R, Buchbinder R. The epidemiology of neck pain. Best Pract Res Clin Rheumatol. 2010;24(6):783-92. Review.
• ⁴
  Martins DE, Astur N, Kanas M, Ferretti M, Lenza M, Wajchenberg M. Quality assessment of systematic reviews for surgical treatment of low back pain: an overview. Spine J. 2016;16(5):667-75. Review.
• ⁵
  Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JP, et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration. Ann Intern Med. 2009;151(4):W65-94.
• ⁶
  Shea BJ, Grimshaw JM, Wells GA, Boers M, Andersson N, Hamel C, et al. Development of AMSTAR: a measurement tool to assess the methodological quality of systematic reviews. BMC Med Res Methodol. 2007;7:10.
• ⁷
  Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics. 1977;33(1):159-74.
• ⁸
  Gwet KL. Handbook of inter-rater-reliability: the definitive guide to measuring the extent of agreement among raters. 4th ed. Gaithersburg: Advanced Analytics, LLC; 2014.
• ⁹
  Kersten RF, van Gaalen SM, de Gast A, Öner FC. Polyetheretherketone (PEEK) cages in cervical applications: a systematic review. Spine J. 2015; 15(6):1446-60. Review.
• ¹⁰
  Jia Z, Mo Z, Ding F, He Q, Fan Y, Ruan D. Hybrid surgery for multilevel cervical degenerative disc diseases: a systematic review of biomechanical and clinical evidence. Eur Spine J. 2014;23(8):1619-32. Review.
• ¹¹
  Riew K, Ecker E, Dettori J. Anterior cervical discectomy and fusion for the management of axial neck pain in the absence of radiculopathy or myelopathy. Evid Based Spine Care J. 2010;1(3):45-50.
• ¹²
  Bakar D, Lubelski D, Abdullah KG, Mroz TE. Artificial cervical disc arthroplasty versus anterior cervical discectomy and fusion: a systematic review. Curr Orthop Pract. 2014;25(1):9-13.
• ¹³
  Cunningham MR, Hershman S, Bendo J. Systematic review of cohort studies comparing surgical treatments for cervical spondylotic myelopathy. Spine (Phila Pa 1976). 2010;35(5):537-43. Review.
• ¹⁴
  Jee YM, Bak JS, Weinlander E, Anderson PA. Comparing nonrandomized observational studies with randomized controlled trials in cervical disc arthroplasty: a meta-analysis. Spine (Phila Pa 1976). 2016;41(5):419-28. Review.
• ¹⁵
  Carrier CS, Bono CM, Lebl DR. Evidence-based analysis of adjacent segment degeneration and disease after ACDF: a systematic review. Spine J. 2013;13(10):1370-78. Review.
• ¹⁶
  Liu FY, Ma L, Huo LS, Cao YX, Yang DL, Wang H, et al. Mini-plate fixation versus suture suspensory fixation in cervical laminoplasty: a meta-analysis. Medicine (Baltimore). 2017;96(5):e6026.
• ¹⁷
  Yoon ST, Hashimoto RE, Raich A, Shaffrey CI, Rhee JM, Riew KD. Outcomes after laminoplasty compared with laminectomy and fusion in patients with cervical myelopathy. Spine (Phila Pa 1976). 2013;38(22 Suppl 1):S183-94. Review.
• ¹⁸
  Bartels RH, Donk R, Verbeek AL. No justification for cervical disk prostheses in clinical practice: a meta-analysis of randomized controlled trials. Neurosurgery. 2010;66(6):1153-60; discussion 1160.
• ¹⁹
  Yuan W, Zhu Y, Liu X, Zhou X, Cui C. Laminoplasty versus skip laminectomy for the treatment of multilevel cervical spondylotic myelopathy: a systematic review. Arch Orthop Trauma Surg. 2014;134(1):1-7. Review.
• ²⁰
  Verhagen AP, van Middelkoop M, Rubinstein SM, Ostelo R, Jacobs W, Peul W, et al. Effect of various kinds of cervical spinal surgery on clinical outcomes: a systematic review and meta-analysis. Pain. 2013;154(11):2388-96. Review.
• ²¹
  Shamji MF, Massicotte EM, Traynelis VC, Norvell DC, Hermsmeyer JT, Fehlings MG. Comparison of anterior surgical options for the treatment of multilevel cervical spondylotic myelopathy: a systematic review. Spine (Phila Pa 1976). 2013;38(22 Suppl 1):S195-209. Review.
• ²²
  Fei Q, Li J, Su N, Wang B, Li D, Meng H, et al. Comparison between anterior cervical discectomy with fusion and anterior cervical corpectomy with fusion for the treatment of cervical spondylotic myelopathy: a meta-analysis. Ther Clin Risk Manag. 2015;11:1707-18.
• ²³
  Liu T, Xu W, Cheng T, Yang HL. Anterior versus posterior surgery for multilevel cervical myelopathy, which one is better? A systematic review. Eur Spine J. 2011;20(2):224-35. Review.
• ²⁴
  Gao F, Mao T, Sun W, Guo W, Wang Y, Li Z, et al. An Updated Meta-Analysis Comparing Artificial Cervical Disc Arthroplasty (CDA) Versus Anterior Cervical Discectomy and Fusion (ACDF) for the Treatment of Cervical Degenerative Disc Disease (CDDD). Spine (Phila Pa 1976). 2015;40(23):1816-23.
• ²⁵
  Harrod CC, Hilibrand AS, Fischer DJ, Skelly AC. Adjacent segment pathology following cervical motion sparing procedures or devices compared to fusion surgery: a systematic review. Spine (Phila Pa 1976). 2012;37(22 Suppl):S96-112. Review.
• ²⁶
  Botelho RV, Moraes OJ, Fernandes GA, Buscariolli YS, Bernardo WM. A systematic review of randomized trials on the effect of cervical disc arthroplasty on reducing adjacent-level degeneration. Neurosurg Focus. 2010;28(6):E5. Review.
• ²⁷
  Lao L, Zhong G, Li X, Qian L, Liu Z. Laminoplasty versus laminectomy for multi-level cervical spondylotic myelopathy: a systematic review of the literature. J Orthop Surg Res. 2013;8(1):8-45. Review.
• ²⁸
  van Limbeek J, Jacobs WC, Anderson PG, Pavlov PW. A systematic literature review to identify the best method for a single level anterior cervical interbody fusion. Eur Spine J. 2000;9:129-36. Review.
• ²⁹
  Wang M, Luo XJ, Deng QX, Li JH, Wang N. Prevalence of axial symptoms after posterior cervical decompression: a meta-analysis. Eur Spine J. 2016;25(7):2302-10. Erratum in: Eur Spine J. 2016;25(6):1968.
• ³⁰
  Liu JM, Peng HW, Liu ZL, Long XH, Yu YQ, Huang SH. Hybrid decompression technique versus anterior cervical corpectomy and fusion for treating multilevel cervical spondylotic myelopathy: which one is better? World Neurosurg. 2015;84(6):2022-9. Review.
• ³¹
  Scherman DB, Mobbs RJ, Phan K. Adjacent segment degeneration and disease following cervical arthroplasty: a systematic review and meta-analysis. J Spine Surg. 2016;2(1):82-4. Review.
• ³²
  Liu FY, Yang SD, Huo LS, Wang T, Yang DL, Ding WY. Laminoplasty versus laminectomy and fusion for multilevel cervical compressive myelopathy: a meta-analysis. Medicine (Baltimore). 2016;95(23):e3588. Erratum in: Medicine (Baltimore). 2016;95(28):e0916. Review.
• ³³
  Zhang J, Meng F, Ding Y, Li J, Han J, Zhang X, et al. Hybrid surgery versus anterior cervical discectomy and fusion in multilevel cervical disc diseases: a meta-analysis. Medicine (Baltimore). 2016;95(21):e3621. Retraction in: Medicine (Baltimore). 2019;98(40):e17483. Erratum in: Medicine (Baltimore). 2016;95(30):e569e. Corrected and republished in: Medicine (Baltimore). 2020;99(5):e19055.
• ³⁴
  Luo J, Huang S, Gong M, Dai X, Gao M, Yu T, et al. Comparison of artificial cervical arthroplasty versus anterior cervical discectomy and fusion for one-level cervical degenerative disc disease: a meta-analysis of randomized controlled trials. Eur J Orthop Surg Traumatol. 2015;25(Suppl 1):S115-25. Review.
• ³⁵
  Molinari RW, Pagarigan K, Dettori JR, Molinari R Jr, Dehaven KE. Return to play in athletes receiving cervical surgery: a systematic review. Glob Spine J. 2016;6(1):89-96.
• ³⁶
  Fouyas IP, Statham PF, Sandercock PA, Lynch C. Surgery for cervical radiculomyelopathy. Cochrane Database Syst Rev. 2001;(3):CD001466. Review. Update in: Cochrane Database Syst Rev. 2006;(2):CD001466.
• ³⁷
  Guan L, Hai Y, Yang JC, Zhou LJ, Chen XL. Anterior cervical discectomy and fusion may be more effective than anterior cervical corpectomy and fusion for the treatment of cervical spondylotic myelopathy. BMC Musculoskelet Disord. 2015;16:29. Review.
• ³⁸
  Dong J, Lu M, Lu T, Liang B, Xu J, Zhou J, et al. Meta-analysis comparing zero-profile spacer and anterior plate in anterior cervical fusion. PLoS One. 2015;10(6):e0130223.
• ³⁹
  Zhu B, Xu Y, Liu X, Liu Z, Dang G. Anterior approach versus posterior approach for the treatment of multilevel cervical spondylotic myelopathy: a systemic review and meta-analysis. Eur Spine J. 2013;22(7):1583-93. Review.
• ⁴⁰
  Tian P, Fu X, Li ZJ, Sun X-L, Ma XL. Hybrid surgery versus anterior cervical discectomy and fusion for multilevel cervical degenerative disc diseases: a meta-analysis. Sci Rep. 2015;5:13454. Review.
• ⁴¹
  Zhao H, Cheng L, Hou Y, Liu Y, Liu B, Mundra JJ, et al. Multi-level cervical disc arthroplasty (CDA) versus single-level CDA for the treatment of cervical disc diseases: a meta-analysis. Eur Spine J. 2015;24(1):101-12. Review.
• ⁴²
  Huang ZY, Wu AM, Li QL, Lei T, Wang KY, Xu HZ, et al. Comparison of two anterior fusion methods in two-level cervical spondylosis myelopathy: a meta-analysis. BMJ Open. 2014;4(7):e004581. Review.
• ⁴³
  Luo J, Cao K, Huang S, Li L, Yu T, Cao C, et al. Comparison of anterior approach versus posterior approach for the treatment of multilevel cervical spondylotic myelopathy. Eur Spine J. 2015;24(8):1621-30. Review.
• ⁴⁴
  Jiang H, Zhu Z, Qiu Y, Qian B, Qiu X, Ji M. Cervical disc arthroplasty versus fusion for single-level symptomatic cervical disc disease: a meta-analysis of randomized controlled trials. Arch Orthop Trauma Surg. 2012;132(2):141-51.
• ⁴⁵
  Han YC, Liu ZQ, Wang SJ, Li LJ, Tan J. Is anterior cervical discectomy and fusion superior to corpectomy and fusion for treatment of multilevel cervical spondylotic myelopathy? A systemic review and meta-analysis. PLoS One. 2014;9(1):e87191. Review.
• ⁴⁶
  Cepoiu-Martin M, Faris P, Lorenzetti D, Prefontaine E, Noseworthy T, Sutherland L. Artificial cervical disc arthroplasty: a systematic review. Spine (Phila Pa 1976). 2011;36(25):E1623-33. Review.
• ⁴⁷
  Fallah A, Akl EA, Ebrahim S, Ibrahim GM, Mansouri A, Foote CJ, et al. Anterior cervical discectomy with arthroplasty versus arthrodesis for single-level cervical spondylosis: a systematic review and meta-analysis. PLoS One. 2012;7(8):e43407. Review.
• ⁴⁸
  Liu X, Wang H, Zhou Z, Jin A. Anterior decompression and fusion versus posterior laminoplasty for multilevel cervical compressive myelopathy. Orthopedics. 2014;37(2):e117-22. Review.
• ⁴⁹
  Gu Y, Cao P, Gao R, Tian Y, Liang L, Wang C, et al. Incidence and risk factors of C5 palsy following posterior cervical decompression: a systematic review. PLoS One. 2014;9(8):e101933. Review.
• ⁵⁰
  Yin S, Yu X, Zhou S, Yin Z, Qiu Y. Is cervical disc arthroplasty superior to fusion for treatment of symptomatic cervical disc disease? A meta-analysis. Clin Orthop Relat Res. 2013;471(6):1904-19.
• ⁵¹
  Jacobs W, Willems PC, Kruyt M, van Limbeek J, Anderson PG, Pavlov P, et al. Systematic review of anterior interbody fusion techniques for single- and double-level cervical degenerative disc disease. Spine (Phila Pa 1976). 2011;36(14):E950-60. Review.
• ⁵²
  Gao Y, Liu M, Li T, Huang F, Tang T, Xiang Z. A meta-analysis comparing the results of cervical disc arthroplasty with anterior cervical discectomy and fusion (ACDF) for the treatment of symptomatic cervical disc disease. J Bone Joint Surg Am. 2013;95(6):555-61.
• ⁵³
  Lee CH, Lee J, Kang JD, Hyun SJ, Kim KJ, Jahng TA, et al. Laminoplasty versus laminectomy and fusion for multilevel cervical myelopathy: a meta-analysis of clinical and radiological outcomes. J Neurosurg Spine. 2015;22(6):589-95. Review.
• ⁵⁴
  Sun Y, Li L, Zhao J, Gu R. Comparison between anterior approaches and posterior approaches for the treatment of multilevel cervical spondylotic myelopathy: a meta-analysis. Clin Neurol Neurosurg. 2015;134:28-36.
• ⁵⁵
  Yu L, Song Y, Yang X, Lv C. Systematic review and meta-analysis of randomized controlled trials: comparison of total disk replacement with anterior cervical decompression and fusion. Orthopedics. 2011;34(10):e651-8. Review.
• ⁵⁶
  Aragones M, Hevia E, Barrios C. Polyurethane on titanium unconstrained disc arthroplasty versus anterior discectomy and fusion for the treatment of cervical disc disease: a review of level I-II randomized clinical trials including clinical outcomes. Eur Spine J. 2015;24(12):2735-45. Review.
• ⁵⁷
  van Middelkoop M, Rubinstein SM, Ostelo R, van Tulder MW, Peul W, Koes BW, et al. No additional value of fusion techniques on anterior discectomy for neck pain: a systematic review. Pain. 2012;153(11):2167-73. Review.
• ⁵⁸
  Zhang Y, Liang C, Tao Y, Zhou X, Li H, Li F, et al. Cervical total disc replacement is superior to anterior cervical decompression and fusion: a meta-analysis of prospective randomized controlled trials. PLoS One. 2015;10(3):e0117826.
• ⁵⁹
  Jiang L, Tan M, Dong L, Yang F, Yi P, Tang X, et al. Comparison of anterior decompression and fusion with posterior laminoplasty for multilevel cervical compressive myelopathy: a systematic review and meta-analysis. J Spinal Disord Tech. 2015;28(8):282-90. Review.
• ⁶⁰
  Lu Y, Hecht AC, Cho S, Qureshi S. Cervical disc arthroplasty versus anterior cervical discectomy and fusion: a systematic review. Orthop Muscul Syst. 2012;S2:002. Review.
• ⁶¹
  Boselie TFM, Willems PC, van Mameren H, de Bie R, Benzel EC, van Santbrink H. Arthroplasty versus fusion in single-level cervical degenerative disc disease. Cochrane database Syst Rev. 2012;(9):CD009173. Update in: Cochrane Database Syst Rev. 2015;(5):CD009173. Review.
• ⁶²
  Wu AM, Xu H, Mullinix KP, Jin HM, Huang ZY, Lv QB, et al. Minimum 4-year outcomes of cervical total disc arthroplasty versus fusion: a meta-analysis based on prospective randomized controlled trials. Medicine (Baltimore). 2015;94(15):e665.
• ⁶³
  Zhong ZM, Zhu SY, Zhuang JS, Wu Q, Chen JT. Reoperation After cervical disc arthroplasty versus anterior cervical discectomy and fusion: a meta-analysis. Clin Orthop Relat Res. 2016;474(5):1307-16. Erratum in: Clin Orthop Relat Res. 2017;475(3):927. Review.
• ⁶⁴
  Rao MJ, Nie SP, Xiao BW, Zhang GH, Gan XR, Cao SS. Cervical disc arthroplasty versus anterior cervical discectomy and fusion for treatment of symptomatic cervical disc disease: a meta-analysis of randomized controlled trials. Arch Orthop Trauma Surg. 2015;135(1):19-28.
• ⁶⁵
  Ren C, Song Y, Xue Y, Yang X. Mid- to long-term outcomes after cervical disc arthroplasty compared with anterior discectomy and fusion: a systematic review and meta-analysis of randomized controlled trials. Eur spine J. 2014;23(5):1115-23. Review.
• ⁶⁶
  Hu Y, Lv G, Ren S, Johansen D. Mid- to Long-Term Outcomes of Cervical Disc Arthroplasty versus Anterior Cervical Discectomy and Fusion for Treatment of Symptomatic Cervical Disc Disease: a Systematic Review and Meta-Analysis of Eight Prospective Randomized Controlled Trials. PLoS One. 2016;11(2):e0149312. Review.
• ⁶⁷
  Gebremariam L, Koes BW, Peul WC, Huisstede BM. Evaluation of treatment effectiveness for the herniated cervical disc: a systematic review. Spine (Phila Pa 1976). 2012;37(2):E109-18. Review.
• ⁶⁸
  Yang B, Li H, Zhang T, He X, Xu S. The incidence of adjacent segment degeneration after cervical disc arthroplasty (CDA): a meta analysis of randomized controlled trials. PLoS One. 2012;7(4):e35032. Review.
• ⁶⁹
  Verma K, Gandhi SD, Maltenfort M, Albert TJ, Hilibrand AS, Vaccaro AR, et al. Rate of adjacent segment disease in cervical disc arthroplasty versus single-level fusion: meta-analysis of prospective studies. Spine (Phila Pa 1976). 2013;38(26):2253-7.
• ⁷⁰
  Xiao SW, Jiang H, Yang LJ, Xiao ZM. Anterior cervical discectomy versus corpectomy for multilevel cervical spondylotic myelopathy: a meta-analysis. Eur Spine J. 2015;24(1):31-9.
• ⁷¹
  Wang T, Wang H, Liu S, Liu H, Ding W. Anterior cervical discectomy and fusion versus anterior cervical corpectomy and fusion in multilevel cervical spondylotic myelopathy. Medicine (Baltimore). 2016;95(49):e5437. Review.
• ⁷²
  Muheremu A, Niu X, Wu Z, Muhanmode Y, Tian W. Comparison of the short- and long-term treatment effect of cervical disk replacement and anterior cervical disk fusion: a meta-analysis. Eur J Orthop Surg Traumatol. 2015;25 Suppl 1:S87-100. Review.
• ⁷³
  Wang L, Wang Y, Yu B, Li Z, Liu X. Open-door versus French-door laminoplasty for the treatment of cervical multilevel compressive myelopathy. J Clin Neurosci. 2015;22(3):450-5. Review.
• ⁷⁴
  Li H, Min J, Zhang Q, Yuan Y, Wang D. Dynamic cervical plate versus static cervical plate in the anterior cervical discectomy and fusion: a systematic review. Eur J Orthop Surg Traumatol. 2013;23 Suppl 1:S41-6. Review.
• ⁷⁵
  Liu X, Min S, Zhang H, Zhou Z, Wang H, Jin A. Anterior corpectomy versus posterior laminoplasty for multilevel cervical myelopathy: a systematic review and meta-analysis. Eur Spine J. 2014;23(2):362-72. Review.
• ⁷⁶
  Xing D, Ma XL, Ma JX, Wang J, Ma T, Chen Y. A meta-analysis of cervical arthroplasty compared to anterior cervical discectomy and fusion for single-level cervical disc disease. J Clin Neurosci. 2013;20(7):970-8.
• ⁷⁷
  Li GL, Hu JZ, Lu HB, Qu J, Guo LY, Zai FL. Anterior cervical discectomy with arthroplasty versus anterior cervical discectomy and fusion for cervical spondylosis. J Clin Neurosci. 2015;22(3):460-7. Review.
• ⁷⁸
  Wen ZQ, Du JY, Ling ZH, Xu HD, Lin XJ. Anterior cervical discectomy and fusion versus anterior cervical corpectomy and fusion in the treatment of multilevel cervical spondylotic myelopathy: systematic review and a meta-analysis. Ther Clin Risk Manag. 2015;11:161-70.
• ⁷⁹
  van Middelkoop M, Rubinstein SM, Ostelo R, van Tulder MW, Peul W, Koes BW, et al. Surgery versus conservative care for neck pain: a systematic review. Eur Spine J. 2012;22(1):87-95. Review.
• ⁸⁰
  Turner JA, Ersek M, Herron L, Deyo R. Surgery for lumbar spinal stenosis. Attempted meta-analysis of the literature. Spine (Phila Pa 1976). 1992;17(1):1-8.
• ⁸¹
  Tashani OA, El-Tumi H, Aneiba K. Quality of systematic reviews: an example of studies comparing artificial disc replacement with fusion in the cervical spine. Libyan J Med. 2015;10(1):28857.
• ⁸²
  Higgins JPT, Green S. Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [Updated March 2011]. vol 4. The Cochrane Collaboration; 2011.

Publication Dates

• Publication in this collection
  20 Apr 2022
• Date of issue
  2022

History

• Received
  28 Feb 2021
• Accepted
  19 July 2021