Cervical Disc Arthroplasty Versus Anterior Cervical ...€¦ · cervical disc disease compared with...

SPINE Volume 41, Number 19, pp 1493–1502

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CERVICAL SPINE

Cervical Disc Arthroplasty Versus AnteriorCervical Discectomy and Fusion for Incidenceof Symptomatic Adjacent Segment Disease

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A Meta-Analysis of Prospective Randomized Controlled Trials

Yuhang Zhu, MD, Boyin Zhang, MD, Haochuan Liu, MD, Yuntao Wu, MD, and Qingsan Zhu, MD, PhD

Conclusion. CDA was superior to ACDF regarding fewer ASDs
Study Design. Meta-analysis of randomized controlled trials.Objective. To evaluate the reported rate of adjacent segment
disease (ASD) of cervical disc arthroplasty (CDA) compared with

anterior cervical discectomy and fusion (ACDF).Summary of Background Data. Motion-maintaining technol-

ogies such as CDA have developed rapidly because of the

concern of ASD. Till date, however, it still has been under

debate whether CDA is superior to ACDF regarding the

incidence of ASD.Methods. We comprehensively searched PubMed, EMBASE,

and Cochrane Central Register of Controlled Trails for prospec-

tive randomized controlled trials (RCTs) that reported the

incidence of ASD between CDA and ACDF. The retrieved results

were last updated on November 20, 2015 without language

restrictions. Two independent authors selected qualified studies,

assessed methodological quality, and extracted requisite data.Results. Fourteen relevant RCTs involving 3235 individuals

with a follow-up period of 2 to 7 years were included in the

meta-analysis (1696 in CDA group and 1539 in ACDF group).

The outcomes indicated that CDA was superior to ACDF

considering the lower rate of ASD (risk ratio, 0.57; 95%

confidence interval, 0.37 to 0.87; P¼0.009). And compared

with ACDF, there were significantly fewer adjacent segment

reoperations in the CDA group (risk ratio, 0.47; confidence

interval, 0.32 to 0.70; P¼0.0002). Subgroup analysis stratified

by different types of disc prostheses was also performed.

the Department of Orthopedics, China-Japan Union Hospital of Jilinrsity, Changchun, China.

wledgment date: December 7, 2015. First revision date: January 12,Acceptance date: February 15, 2016.

ticle submitted does not contain information about medical device(s)/).

nds were received in support of this work.

levant financial activities outside the submitted work.

ss correspondence and reprint requests to Qingsan Zhu, MD, PhD,tment of Orthopedics, China-Japan Union Hospital of Jilin University,chun, China; E-mail: [email protected]

10.1097/BRS.0000000000001537

yright © 2016 Wolters Kluwer Health, Inc. Unau

and relative reoperations on the basis of available evidence from

a meta-analysis of 14 RCTs. CDA may be a better surgical

procedure to reduce the incidence of ASD for patients with

cervical disc disease compared with ACDF. Further well-

designed studies should continue to pay attention to excellent

patients with longer-term follow-up to evaluate the incidence of

ASD of these two procedures.Key words: adjacent segment disease, anterior cervicaldiscectomy and fusion, cervical disc arthroplasty, discprostheses, randomized controlled trials.Level of Evidence: 1Spine 2016;41:1493–1502

nterior cervical discectomy and fusion (ACDF) is a

A conventional and well-accepted surgical procedureas the ‘‘gold standard’’ to treat symptomatic cer-

vical disc disease. Clinical studies have reported high successrates, favorable outcomes, and relief of symptoms afterACDF.1–3 However, there is evidence showing that ACDFmay result in adjacent segment degeneration (radiographicchanges of degeneration at levels adjacent to a spinal fusion)and adjacent segment disease (development of new symp-toms correlating with adjacent segment degeneration).4

Some biomechanical studies also indicate that the adjacentlevels of fusion may suffer higher articular surface load andkinematic strain leading to mechanical instability anddisc generation,5,6 for which additional operations areoften needed.

Cervical disc arthroplasty (CDA) has become a progress-ively popular surgical procedure to substitute ACDF inrecent years. The purposes of CDA are to accomplish thesame neural decompression as that of conventional fusionsurgery and to restore disc height and maintain the motionof joint. Thus, it can normalize the kinematics of cervicalspine in theory and possibly retard degeneration of adjacentsegments. However, a few clinical studies have specificallyaimed to assess the incidence of adjacent segment disease(ASD) after CDA.

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CERVICAL SPINE Cervical Disc Arthroplasty Versus Anterior Cervical Discectomy and Fusion � Zhu et al

A few previous meta-analyses38–40 have focused on thisscope, but they have different conclusions about whetherarthroplasty in cervical spine will accomplish its primarypurposes to improve clinical outcomes and reduce ASDs. Toclarify this debate further, we made a search of availablepublished data and performed a meta-analysis to comparethe rate of ASD between CDA and ACDF.

MATERIALS AND METHODS

Search StrategyTo make an exhaustive search of all relevant literatures,two independent reviewers (Y.H.Z. and B.Y.Z.) conducteda PRISMA (Preferred Reporting Items for SystematicReviews and Meta-Analyses) compliant search of PubMed,EMBASE, and Cochrane Central Register of ControlledTrails (CENTRAL). The following Mesh and free textsearch terms included: ‘‘anterior cervical decompressionand fusion,’’ ‘‘cervical arthrodesis,’’ ‘‘disc replacement,’’‘‘disc prostheses,’’ and ‘‘cervical arthroplasty’’ with a limitof ‘‘clinical trial.’’ The retrieved results were last updatedon November 20, 2015 without language restrictions.References cited in the relevant literatures were alsoreviewed.

Criteria for Selecting TrialsWe included studies that were eligible for the followingcriteria: (i) randomized controlled trial (RCT) of comparingcervical arthroplasty and cervical arthrodesis; (ii) patientswere definitely diagnosed with ASD or suffered adjacentsegment reoperations; (iii) the individuals were older than18 years; (iv) a minimum of 2-year follow-up. The exclusioncriteria were as follows: (i) case reports, reviews, or obser-vational studies; (ii) descriptive or graphic outcomes with nonumerical values; (iii) only evidence of radiographicdegeneration at adjacent segments; (iv) the same data hadbeen published repeatedly. Two reviewers (Y.H.Z. andH.C.L.) independently selected the potentially qualifiedtrials according to the inclusion and exclusion criteria.Any disagreement was resolved by discussion and conform-ity was reached.

Data ExtractionTwo independent reviewers (Y.H.Z. and Y.T.W.) extractedthe data from eligible studies. Any discrepancy was eitherresolved by discussion or by involving a third reviewer(Q.S.Z.) when necessary until a consensus for all itemswas achieved. The indispensable data extracted fromeligible researches included the study design, interventiondetails, sample size, age, sex distribution, missing size, andduration of follow-up. The pooled outcomes included therate of ASD and adjacent segment reoperation. Although therate of reoperation at adjacent segments is not synonymouswith ASD, it indirectly reflects the incidence of ASD and weutilized it also as a secondary assessment standard. Inaddition, we did subgroup analysis stratified by differenttypes of disc prostheses.

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Quality AssessmentTwo reviewers (Y.H.Z. and B.Y.Z.) independently used the12 criteria recommended by the Cochrane Back ReviewGroup to assess the risk of bias of included studies.7 Theevaluation details of 12 criteria were based on a previousmeta-analysis of Wei et al.8 If at least six of the criteria wentthrough without serious flaws; studies were defined asmeeting ‘‘low risk of bias.’’ If not, we defined the studiesas having ‘‘high risk of bias.’’ Moreover, the GRADE(Grades of Recommendation, Assessment, Development,and Evaluation) approach was used to rate the strengthof evidence for all pooled outcomes. According to theassessment of study design, risk of bias, consistency, direct-ness, and precision, the quality of outcomes was categorizedas very low, low, moderate, or high.9

Statistical AnalysisThe x2 test and I2 test were used to assess the statisticalheterogeneity. It demonstrated significant heterogeneitywhen a P value of the x2 test was less than 0.10 or I2 valuesexceeded 50%. A random effects model was used whensignificant heterogeneity was observed among the includedstudies. Otherwise, a fixed-effects model was used for nosignificant heterogeneity. Only dichotomous data werepooled in this study, so the risk ratio (RR) and its 95%confidence interval (CI) were calculated. The funnel plotsand Egger tests were used to assess the possibility of pub-lication bias. Sensitivity analyses were executed only formulticenter studies. This meta-analysis was performed byRevMan 5.3 software (Cochrane Collaboration, Copenha-gen, Denmark), and the Egger test was accomplished byStata 13.0 (Stata Corporation, College Station, TX). Thestatistically significant level was set at P<0.05.

RESULTS

Search ResultsThe process of identifying relevant studies was displayed inFigure 1. A total of 453 relevant researches were initiallyinspected from PubMed (N¼149), EMBASE (N¼151),CENTRAL (N¼141), and reference lists (N¼12). Thenumber of 164 trials was remained after excluding theduplicates. After reviewing the titles and abstracts, 115trials were excluded because they did not reach the standardof inclusion criteria. A full text review was accessed in theretaining 49 studies, and finally, 14 RCTs10–23 with 3235individuals (CDA¼1696, ACDF¼1539) were included inthis meta-analysis. We recorded the extracted data of thecharacteristics of 14 included papers (Table 1), and thesupplementary characteristics and details (Table 2).

Quality AssessmentAccording to the 12 criteria of assessing the risk of bias, 11studies with ‘‘low risk of bias’’ and three study with ‘‘highrisk of bias’’ were indicated (Figure 2). Most of the biasesfocused on lacking of adequate allocation concealment,detailed blinding methods and intend to treat analysis.

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Figure 1. Flow diagram of selecting relevantstudies.


According to the GRADE approach, four pooled outcomesshowed moderate quality evidences and three displayed low-quality evidences (Table 3).

Analysis of Pooled OutcomesEight studies with a total of 1346 patients (708 in CDAgroup and 638 in ACDF group) were pooled in the outcomeof ASD. The rate of ASD in the CDA group was significantlylower than that in the ACDF group (RR, 0.57; 95% CI, 0.37to 0.87; P¼0.009) with no obvious heterogeneity (P¼0.66,I2¼0%) (Figure 3).

Ten studies with a total of 2416 patients (1250 in CDAgroup and 1166 in ACDF group) were analyzed in adjacentsegment reoperation. There were fewer adjacent segmentreoperations in the CDA group compared with the ACDFgroup (RR, 0.47; CI, 0.32 to 0.70; P¼0.0002) with lowheterogeneity (P¼0.13, I2¼35%). After sensitivity analysis,the heterogeneity substantially decreased (P¼0.55, I2¼0%)and CDA still had fewer adjacent segment reoperations thanACDF (RR, 0.61; CI, 0.40 to 0.94; P¼0.02) (Figure 4).

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In addition, subgroup analysis stratified by different typesof prostheses was performed (Figure 5). CDA with Bryandisc presented no significant difference compared withACDF regarding ASD (RR, 0.37; CI, 0.08 to 1.77;P¼0.21) or adjacent segment reoperation (RR, 0.72; CI,0.35 to 1.51; P¼0.39). Similarly, there was no significantdifference in ASD between CDA with ProDisc-C disc andACDF (RR, 0.34; CI, 0.08 to 1.41; P¼0.14). However,CDA with Prestige disc displayed significant lower rate ofASD than ACDF (RR, 0.42; CI, 0.21 to 0.82; P¼0.01)(Table 4).

Publication BiasThe funnel plots for ASD indicated no obvious evidence ofpublication bias (Figure 6A), and the Egger test also showedno evidence of publication bias (t¼ –0.66, P¼0.548).However, the funnel plots for adjacent segment reoperationdisplayed the possibility of publication bias (Figure 6B) withwhich the result of Egger test was consistent (t¼ –2.81,P¼0.026).



TABLE 1. Characteristics of the Studies Included in the Analysis

StudiesPublished

Year DesignSample Size(CDA/ACDF)

Mean Age(CDA/ACDF)

Sex(Male/Female)(CDA/ACDF)

Missing Size(CDA/ACDF)

Porchet et al10 2004 RCT 4 sites 55 (27/28) 44/43 (17/10)/(12/16) 9/9

Nabhan et al11 2007 RCT 1 site 41 (20/21) 44 23/18 1/0

Garrido et al12 2010 RCT 1 site 47 (21/26) 40/43 (13/8)/(17/9) 3/6

Coric et al13 2010 RCT 1 site 98 (57/41) 46.6/46.3 (22/31)/(16/21) 4/4

Coric et al14 2011 RCT 21 sites 269 (136/133) 43.7/43.9 (51/85)/(59/74) 17/18

Sasso et al15 2011 RCT 30 sites 463 (242/221) 44/44.7 (110/132)/(113/108) 61/83

Zhang et al16 2012 RCT 3 sites 120 (60/60) 44.8/45.6 (35/25)/(32/28) 4/7

Nunley et al17 2012 RCT 2 sites 182 (120/62) 45/43 (57/63)/(27/35) 7/5

Delamarter et al18 2013 RCT 13 sites 209 (103/106) 42.1/43.5 (46/57)/(49/57) 31/45

Burkus et al19 2014 RCT 31 sites 541 (276/265) 43.3/43.9 (128/148)/(122/143) 64/82

Zhang et al20 2014 RCT 11sites 111 (55/56) 44.8/46.7 (25/30)/(26/30) NR

Skeppholm et al21 2015 RCT 3 sites 151 (81/70) 46.7/47.0 (40/41)/(33/37) 5/9

Phillips et al22 2015 RCT 24 sites 403 (218/185) 45.3/43.7 (113/105)/(96/89) 55/62

Gornet et al23 2015 RCT 20 sites 545 (280/265) 44.5/43.9 (129/151)/(122/143) 8/42

ACDF indicates anterior cervical discectomy and fusion; CDA, cervical disc arthroplasty; NR, not reported.


Sensitivity Analysis by All Multicenter StudiesIn 14 included RCTs, three single-center studies11–13 basedon small sample size were excluded in the sensitivityanalysis. Six multicenter studies reported the incidence ofASD and eight reported the incidence of adjacent segmentreoperation (Figure 7). There were fewer ASDs in the CDAgroup compared with the ACDF group (RR, 0.58; 95% CI,0.38 to 0.91; P¼0.02). Moreover, the rate of adjacentsegment reoperation in the CDA group was significantlylower than that in the ACDF group (RR, 0.48; 95% CI, 0.32to 0.73; P¼0.0006). Sensitivity analyses indicated the

TABLE 2. Supplementary Characteristics and Clini

Studies

Numberof Involved

Levels

Patientsof ASD

(CDA/ACDF)R(C

Porchet et al10 1 0/2

Nabhan et al11 1 0/1

Garrido et al12 1 1/3

Coric et al13 1 or 2 NR

Coric et al14 1 NR

Sasso et al15 1 NR

Zhang et al16 1 1/3

Nunley et al17 1 or 2 19/9

Delamarter et al18 1 2/6

Burkus et al19 1 11/24

Zhang et al20 1 NR

Skeppholm et al21 1 or 2 2/2

Phillips et al22 1 NR

Gornet et al23 1 NR

ACDF indicates anterior cervical discectomy and fusion; CDA, cervical disc arthro



robustness of the rates of adjacent segment disease andreoperation in multicenter studies compared with the pooledresults in all included studies.

DISCUSSIONAlthough ACDF is considered to be the ‘‘gold standard’’ totreat symptomatic myelopathy and/or radiculopathy withnotable curative effect, ASD emerges gradually as a commoncomplication. Hilibrand et al1 reported the rate of sympto-matic ASD as 2.9% per year and 25.6% for 10-year follow-up after cervical fusion. Similarly, Cho et al24 reported the

cal Details of Included Studies

Events ofeoperationsDA/ACDF)

FollowUp

(Years) Disc Type

NR 2 Prestige II

NR 3 ProDisc-C

1/3 4 Bryan

1/3 2 Bryan, Discover orKineflex C

9/7 2 Kineflex C

10/10 4 Bryan

1/3 2 Bryan

NR 4 Kineflex C, Mobi-C orAdvent

2/8 5 ProDisc-C

NR 7 Prestige

0/4 4 Mobi-C

2/3 2 Discover

1/17 5 PCM

7/11 2 Prestige LP

plasty; NR, not reported.

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Figure 2. Risk of bias of included studies.

TABLE 3. Summary of Strength of Evidence With R

Outcomes Studies

Patients(CDA/ACDF) Risk of Bias

ASD 8 841/744 Serious�

ASD (Bryan) 2 81/86 Serious�

ASD (Prestige) 2 303/293 Serious�

ASD (ProDisc-C) 2 123/127 Serious�

Adjacent segmentreoperation

10 1250/1166 Serious�

Adjacent segmentreoperation(Bryan)

3 323/307 Serious�

Adjacent segmentreoperationz

9 1032/981 Serious�

ACDF indicates anterior cervical discectomy and fusion; ASD, adjacent segment d�Serious risk of performance bias, detection bias, or attrition bias.yWide confidence intervals are around the estimate of the effect or total populatiozAdjacent segment reoperation after the sensitivity analysis.


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incidence of ASD as 3% annually and 25% within the first10 years after fusion. Lee et al25 indicated that secondarysurgery at adjacent segments occurred at a rate of 2.4% peryear and predicted that 22.2% of patients would needadjacent segment reoperations by 10 years postoperation.The definite risk factor of causing adjacent segment degener-ation is still unclear. Some studies indicate that postoper-ative disc height, congenital stenosis, and postoperativekyphotic change may be risk factors for developing radio-graphic degeneration at adjacent segments after ACDF.33–35

Additional plate augmentation for ACDF can lower the rateof ASD, and factors increasing the risk of secondary surgeryat adjacent segments were smoking, female sex, and thenumber of arthrodesis segments.36 In a RCT study compar-ing ACDF with CDA, Nunley et al17 reported that osteo-penia and concurrent lumbar degeneration diseasesignificantly increased the risk of ASD after anterior cervicalsurgery. It is also indicated that patients are more likely todevelop ASD and adjacent segment degeneration at thesuperior adjacent level compared with the inferior adjacentlevel.26–28 It remains under debate whether ASD caused byspinal fusion attributes to iatrogenic motion restriction.4,29

However, Matsumoto et al30 compared 64 patients with201 asymptomatic volunteers for 10-year follow-up, andfound that ACDF patients had significantly higher incidenceof disc degeneration at adjacent segments than asympto-matic volunteers, which implied that ACDF could acceleratethe nature history of spinal segmental degeneration. Theoriginal design purpose of CDA is to maintain the motion ofjoint, so it can normalize the kinematics of cervical spinetheoretically and possibly retard adjacent segment degener-ation. CDA has demonstrated the advantage of keepingnormal motion and reducing intradiscal pressure and facetloads at adjacent segments in some in vitro biomechanicalstudies.5,6,31,32 However, it still lacks of sufficient clinical

egard to the Outcomes

Inconsistency Indirectness Imprecision Quality

No No No Moderate

No No Seriousy Low

No No No Moderate

No No Seriousy Low

No No No Moderate

No No Seriousy Low

No No No Moderate

isease; CDA, cervical disc arthroplasty.

n size is less than 400.



Figure 3. Forest plot comparing the incidence of adjacent segment disease between cervical disc arthroplasty and anterior cervical discectomyand fusion. CI indicates confidence interval; df, degrees of freedom; MH, Mantel-Haenszel.


evidences to prove that CDA is superior to ACDF regardinglower rate of ASD.

In our meta-analysis, we selected 14 RCTs comparingACDF with CDA that specifically reported the rate ofsymptomatic ASD or adjacent segment reoperation at thefollow-up of two to seven years. And two studies17,18

mainly aimed to report the rate of ASD and relativereoperation. Studies with only data of radiographic changesof degeneration at adjacent levels were not included,because a simple observation of ossification at adjacentsegments cannot be directly correlated to the development

Figure 4. Forest plot comparing the incidence of adjacent segment rediscectomy and fusion. CI indicates confidence interval; df, degrees of fre



of symptomatic disease.37 Eight different types of discprostheses were involved in the pooled CDA group. Phillipset al22 reported a relatively low rate of adjacent segmentreoperation in the CDA group in a RCT study comparingPCM prosthesis with ACDF. This study resulted in quan-titative heterogeneity in the pooled outcome and wasremoved in the sensitivity analysis. In the subgroupanalysis, Bryan and ProDisc-c prostheses were equivalentto ACDF regarding the incidence of ASD, respectively.Only Prestige prosthesis showed fewer ASDs comparedwith cervical fusion, which implied that the different

operation between cervical disc arthroplasty and anterior cervicaledom; MH, Mantel-Haenszel.

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Figure 5. Subgroup analyses of the incidences of adjacent segment disease and reoperation by different prosthesis types. CI indicatesconfidence interval; df, degrees of freedom; MH, Mantel-Haenszel.


prosthesis types might influence the rate of ASD. However,the validity of subgroup analysis was limited by low qualityevidences in GRADE approach because of risk of bias andimprecisions.

There have been a few meta-analyses comparing thesafety and efficacy between ACDF and CDA. Yanget al38 and Verma et al39 respectively performed a meta-analysis involving six RCTs to compare the radiographicadjacent segment degeneration or symptomatic ASDbetween the two surgical procedures. These two studieswere both current up to 2011 and indicated no significantdifference in the incidence of ASD when comparing ACDF

TABLE 4. Pooled Results in the Subgroup Analysis

OutcomesSample

Size ModelRR

(95%

ASD (Bryan) 167 Fixed 0.37 (0.08

ASD (Prestige) 596 Fixed 0.42 (0.21

ASD (ProDisc-C) 250 Fixed 0.34 (0.08

Adjacent segmentreoperation (Bryan)

630 Fixed 0.72 (0.35

ASD indicates adjacent segment disease; CDA, cervical disc arthroplasty; CI, conf

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with CDA. However, four new RCTs16,20–22 reporting therate of ASD have been published in recent 4 years, and threeoriginal RCTs17–19 have updated new outcome in longer-follow-up period. Luo et al40 reported that CDA had fewerASDs than ACDF in a recent meta-analysis. However, itonly included eight RCTs, and the rates of radiographicdegeneration and symptomatic disease at adjacent segmentswere pooled together into the outcome. Moreover, all theprevious meta-analyses ignored the subgroup analysis ofdifferent prosthesis types.

There are a few strengths in our study. First, this is thelatest and most comprehensive meta-analysis to evaluate the

of Different Prosthesis Types

CI) I2 (%) Pheterogeneity P Favor

–1.77) 0 0.89 0.21 No difference

–0.82) 0 0.63 0.01 CDA

–1.41) 0 0.99 0.14 No difference

–1.51) 0 0.61 0.39 No difference

idence interval; RR, risk ratio.



Figure 6. (A) Funnel plots for the adjacent segment disease. (B) Fun-nel plots for the adjacent segment reoperation.

Figure 7. Sensitivity analyses of the incidences of adjacent segment diseainterval; df, degrees of freedom; MH, Mantel-Haenszel.




incidence of ASD between CDA and ACDF. Second, weused Cochrane risk of bias and GRADE approach to assessthe quality of evidence. Additional strengths contained arigorous search strategy, only RCTs included, no languagelimitations, sensitivity analysis, and subgroup analysisstratified by different types of prostheses to guarantee theconsistency and accuracy. However, the validness of ourstudy is limited by several factors. First, the pooled outcomeof adjacent segment reoperation indicated the possibility ofpublication bias. Second, the results of subgroup analysisshould be cautiously accepted because of low quality evi-dences. Third, various surgery interventions and surgicaltechnologies at different centers may influence the outcome.Moreover, the follow-up period of six included RCTs is 2years, and this period is too short to assess a comprehensiverate of ASD. So these studies should continue to focus onreporting the incidence of ASD in longer-follow-up period.During our search of relevant studies, ASD was not men-tioned in some studies, which were designed as RCTs toevaluate the effectiveness and safety of disc prostheses andonly focused on the improvement of symptoms at thesurgical segment. So this study also aims to highlight theimportance of considering ASD as an outcome in futureprospective studies.

In summary, our meta-analysis indicated that CDA wassuperior to ACDF regarding fewer ASDs and adjacentsegmental reoperations. Compared with ACDF, CDAmay be a better surgical procedure to reduce the incidenceof ASD for patients with cervical disc disease. Further well-designed studies should continue to focus on excellentpatients with longer-term follow-up to evaluate the inci-dence of ASD of these two procedures.

se and reoperation in all multicenter studies. CI indicates confidence

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Sp

Co

Key Points

ine

py

This meta-analysis of prospective randomizedcontrolled studies provided the latest evidenceof comparing the incidence of ASD between CDAand ACDF.

Compared with ACDF, CDA presented fewersymptomatic ASDs and relevant adjacentsegment reoperations.

The different types of disc prostheses may affectthe incidence of ASD.

More high quality studies with longer follow-upare needed to explore the occurrence of ASD ofthese two surgical procedures.

rig

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October 2016


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