Systematic Review / Meta-AnalysisClinical risk factors associated with the development of adjacent segment disease in patients undergoing ACDF: A systematic review
Introduction
Cervical spine fusion is a common surgical procedure for degenerative spinal disorders [1,2]. However, these procedures carry some risk of developing adjacent segment degeneration which might be related to the reduction of segmental motion after fusion [3]. Radiographic findings of adjacent segment degeneration include loss of intervertebral disc height, vertebral body endplate sclerosis, osteophyte formation, and longitudinal ligament calcification [4]. Adjacent segment disease (ASD) of the cervical spine refers to degeneration of the adjacent segment above or below the index of cervical fusion that is clinically significant, causing a combination of neck pain, cervical radiculopathy, or cervical myelopathy [5]. The reported incidence of ASD varies widely in the literature, ranging from 2.9% to 92% [6], [7], [8]. ASD carries a significant clinical burden and accounts for around 40% of reoperations after spine surgery [9]. Proposed risk factors for development of ASD include both clinical and radiographic patient characteristics [10]. Assessment of the impact of these risk factors has been limited by difficulty in obtaining sufficient small sample size due to the need for long-term follow-up and the relatively low annual incidence of ASD. Therefore, each individual study reported in the literature suffers from small sample sizes. The aim of this systematic review was to analyze clinical studies on ASD after cervical fusion to better understand the clinical risk factors associated with development of adjacent segment disease in the cervical spine.
Section snippets
Data sources
We systematically reviewed the literature according to the Preferred Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and protocol. The literature search was performed on December 24, 2019. PubMed, Embase, Medline, Scopus, and the Cochrane library were queried from their date of inception using the search terms āadjacent segment*ā and āadjacent level*ā. No additional filters were used in an effort to maximize search yield and sensitivity. The publications were screened for
Included studies
A total of 13,562 records were obtained in the initial search of which 6,850 records remained after duplicate removal (Fig. 1). Screening by title and abstract resulted in 144 articles for full text review. Ninety-five studies were excluded based on the criteria listed above, and an additional nine studies were excluded due to inability to use data. Ten studies were included for final analysis (Table 1), all of which were retrospective studies [8,10,[17], [18], [19], [20], [21], [22], [23], [24]
Evidence summary
The GRADE criteria were used to determine the quality of evidence for each risk factor in the meta-analysis. In this study, the quality of evidence ranged from moderate to very low and are summarized in Table 3. The biggest limitation to higher certainty assessments was risk of methodological bias as determined by the MINORS scores, with inconsistency of results and imprecision also impacting quality of evidence to a lesser degree. There were no concerns for publication bias or indirectness of
Discussion
Investigations into the clinical risk factors associated with the development of cervical ASD have been mostly limited to single cohort studies and literature reviews. In the current systematic review and meta-analysis, we assessed the association between several potential clinical risk factors and development of ASD after cervical spine surgery. Advanced age, congenital stenosis, high preoperative NDI scores, and high preoperative VAS scores of the neck and arm to be predisposing factors for
Limitations
Our study has limitations. As with any systematic review of the literature, data analysis is limited by the heterogeneity of methodology and methodological quality of the included studies. The sparse reporting on clinical risk factors for ASD in the literature poses a challenge to controlling for confounding variables. Among the variables analyzed in this review, several of the risk factors we investigated were only reported in two of the included studies which reduces the power of our analysis
Conclusion
This study provides a comprehensive review of clinical risk factors for ASD development after fusion for degenerative disorders of the cervical spine. Age, congenital/developmental stenosis, and high preoperative NDI, VAS (arm), and VAS (neck) clinical outcomes scores were found to be statistically significant clinical risk factors for development of ASD following cervical fusion. The overall quality of evidence is limited due to a considerable heterogeneity of the current literature as well as
Declarations of Competing Interests
One or more of the authors declare financial or professional relationships on ICMJE-NASSJ disclosure forms.
Acknowledgments
This study was organized by AO Spine through the AO Spine Knowledge Form Degenerative, a focused group of international spine degenerative experts. AO Spine is a clinical division of the AO Foundation, which is an independent medically-guided not-for-profit organization.
There was no financial support for this study. No authors receive financial compensation related to the subject matter of this study. Financial disclosures unrelated to the subject matter include: consulting fees (ZB: Cerpaedics
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FDA device/drug status: Not applicable.
Author disclosures: SEB: Nothing to declare. KM: Nothing to disclose. AA: Nothing to disclose. H-JM: Nothing to disclose. PH: Nothing to disclose. JW: Board of Directors: AO Foundation (C), National Spine Health Foundation (Nonfinancial); Consulting: Precision OS (None); Fellowship Support: AOSpine North America (E, Paid directly to institution/employer); Private Investments: Bone Biologics (51,255 Shares, 1%, 51,255 options, <1%), Pearl Driver (25,000 Shares, 1%, 25,000 options, <1%), Surgitech (1 Shares, 1%, <1%); Royalties: Biomet (E), DePuy Synthes (B), SeaSpine (C). AJ: Nothing to disclose. ZB: Board of Directors: LSRS (Nonfinancial, Co-chair of Educational Committee); Consulting: Cerapedics (B, past, Outside 24-Month Requirement); Grants: AO Spine (C, co-PI on a AOSpine Knowledge Forum grant, Paid directly to institution/employer), SBIR NIH (F, Paid directly to institution/employer); Research Support (Staff and/or materials): Medical Metrics (B, Research support includes both investigator and staff salary, Paid directly to institution/employer), MiMedx (F, Paid directly to institution/employer), Next Science (F, Research Support used for Investigator Salary, Staff Salary and Materials, Paid directly to institution/employer), Nexus Spine (B, Paid directly to institution/employer), SeaSpine (F, Research Support - used for Investigator Salary, Staff Salary and Materials, Outside 24-Month Requirement, Paid directly to institution/employer); Scientific Advisory Board: Medtronic (B); Trips/Travel: AO Spine (Travel Expense Reimbursement, travel reimbursements for AO Spine Knowledge forum meetings and congresses), NASS (Travel Expense Reimbursement). STY: Grants: AOSpine(None); Biomet (None); Smith & Nephew (None); NuVasive (None). Consulting: Medtronic (None)