These analyses indicate that primary subaxial cervical arthrodesis has a probability of revision approaching 13% at 16 years after the initial procedure. Multivariate analysis identified a number of demographic, clinical, and surgical factors that were independently associated with revision risk. For instance, younger patient age, Workers’ Compensation insurance status, and anterior approaches were associated with increased revision risk, but shorter arthrodeses and arthrodeses for a diagnosis of fracture had relatively lower revision risk.
The finding that longer arthrodeses, especially when performed via an anterior approach, are associated with higher risk of reoperation falls in line with current clinical teaching, which typically favors posterior or circumferential approaches in the setting of arthrodeses spanning ≥3 levels17. Elevated revision rates in the setting of longer arthrodeses may be due to increased risk of pseudarthrosis and/or increased biomechanical demands placed on the adjacent segments with resulting degeneration18-20. Expansive anterior arthrodeses may be particularly prone to failure because of the risk of dislodgement or migration of long strut grafts or mechanical failure of fixation devices21,22. However, the finding that anterior approaches for 1 and 2-level arthrodeses were associated with an elevated long-term rate of reoperation, even after controlling for surgical indication, age, comorbidities, and a variety of other factors, was unanticipated and warrants future investigation.
Prior studies have focused on the effect of surgical approach on the subsequent revision risk after cervical spine surgical procedures. A 60-month longitudinal investigation of the Washington State inpatient database published in 2009 suggested that nearly 10% of patients who had a surgical procedure for degenerative cervical spine disease underwent reoperation by 60 months from the index procedure, similar to that observed in the New York population9. A more recent analysis of the MarketScan database revealed that patients undergoing arthrodesis for multilevel degenerative cervical disease were less likely to undergo reoperation if the surgical procedure was performed from an anterior approach rather than from a posterior approach8. However, the mean follow-up for that cohort was 18.6 months, with a median time to revision of 20.7 months. These shorter-term findings mirror those observed in the SPARCS database, where there was an early trend toward fewer revisions in the anterior group, but the cumulative revision rate for anterior approaches began to exceed that of posterior approaches at longer follow-up. Lee et al. reported specifically on revision for adjacent-segment disease and found that arthrodeses performed from a posterior approach had a 3 times greater risk of revision compared with those performed from an anterior approach23. Because the mean follow-up was 48 months (range, 12 to 168 months), it was more difficult to reconcile these findings with our own, although limiting their end point to revision for adjacent-segment disease may have contributed to this difference. Meanwhile, a meta-analysis comparing anterior and posterior approaches for the treatment of multilevel cervical spondylotic myelopathy found a higher revision rate in the anterior group, but reoperation figures were founded solely on studies comparing anterior arthrodeses with laminoplasty in the absence of arthrodesis6.
There is discordance within the literature on the survivorship of single-level cervical spine arthrodeses. Veeravagu et al. observed a 10.7% rate of revision at 24 months for anterior cervical discectomy and fusion12, Delamarter and Zigler found a 14.5% revision rate at 60 months24, and Singh et al. reported a reoperation rate of only 7.6% at 144 months25. This variation may be due in part to differences in surgeon preferences and patient factors (for example, demographic characteristics, comorbidities, and attitudes) that impact the decision on whether or not to perform revision surgical procedures. As such, it is difficult to define a consistent figure for the long-term revision rate of cervical spine arthrodesis on the basis of the prior literature.
This study has several characteristics that distinguish it from previous publications. It is based on a large database that does not rely on population sampling, unlike many of the nationwide databases26. The MarketScan database, for instance, is a non-random convenience sample, which is subject to sampling bias27. Instead, SPARCS contains nearly 100% of the procedures performed annually in a large U.S. population. SPARCS has the added benefit of including unique patient identifiers that permit investigators to track patients over time; this is not the case for the National Inpatient Sample (NIS) or the National Surgical Quality Improvement Program (NSQIP), two widely utilized nationwide databases26,28,29. As mentioned earlier, Washington State data were used in the past by King et al. to investigate similar subject matter9. The study presented herein differs from and improves upon that investigation in a number of key aspects. First, New York is one of the most populous states in the country, with a diverse population exceeding 2.5 times the size of the State of Washington30. Furthermore, analysis of 16 years of New York data (1997 to 2012) compared with 5 years of Washington data (1998 to 2002) allowed for substantially longer longitudinal tracking of the New York cohort and inclusion of more recent procedures. King et al. examined cervical spine operations for degenerative disease only; patients with diagnoses of infection, inflammatory spondyloarthropathy, malignancy, and trauma were excluded. Incorporating these diagnoses into the New York investigation allowed for a more comprehensive analysis of surgery for cervical spine disease. Finally, the use of life tables to censor New York patients at their predicted time of death is an improvement upon the methodology utilized in the prior study.
A number of limitations were present in this study, many of which are inherent to population-based database research, where the rigor of the final analysis is dependent on the quality of the initial administrative coding and database methodology. ICD-9-CM codes lack the granularity necessary to make some clinical distinctions (for example, arthrodesis technique and precise levels involved) that would have been interesting to consider had it been possible. In the future, studies employing ICD-10 (International Statistical Classification of Diseases and Related Health Problems, Tenth Revision) data may be capable of better addressing these questions and others. Reliance on administrative data also necessitated the use of revision arthrodesis as a proxy for surgical durability. However, in reality, the decision on whether or not to perform these revision operations is affected by factors such as radiographic findings, symptom severity, patient preferences, and surgeon discretion, which could not be captured in the available data. It would have also been useful to have been able to adjust for radiographic findings (for example, kyphosis) prior to the index surgical procedure, as this can affect the choice of surgical approach. As a state database, SPARCS only contains information on events taking place within medical institutions in New York; any deaths or revision procedures occurring elsewhere are not captured. The study population was limited to New York residents (ostensibly less likely to seek care outside the state border) and life spans were adjusted using life tables to help to address this issue; however, some residual bias toward underestimating revision probabilities may remain. Furthermore, unique patient identifiers for individuals with a diagnosis of AIDS or a previously terminated pregnancy are not released in the SPARCS data set to protect patient privacy. As such, 553 patients with AIDS and 5 with a history of pregnancy termination had to be excluded from our analysis. These individuals would have represented <0.6% of the study cohort, but their absence did limit the generalizability of our results toward patients with these two characteristics. Finally, this study considered a relatively large number of variables and therefore runs the risk of over-fitting. However, the large sample size of the cohort was sufficient to provide robust estimates for the purpose of exploratory analysis.
In conclusion, this study demonstrates that primary subaxial cervical spine arthrodesis has a probability of revision approaching 13% over a period of 16 years, with elevated reoperation rates in patients undergoing an anterior-only surgical procedure. Patient age, race, insurance status, surgical indication, and arthrodesis length were associated with reoperation risk. Knowledge of these factors should help to promote exploration of strategies to reduce the prevalence of revision surgical procedures and to facilitate more accurate preoperative counseling of patients and their relatives.
Tables showing the ICD-9-CM codes utilized to identify the study cohort, operative approaches, revision surgical procedures, and surgical indications are available with the online version of this article as a data supplement at jbjs.org.
Investigation performed at the Hospital for Special Surgery, New York, NY
Disclosure: This study was conducted without an external source of funding. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work.
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Copyright 2016 by The Journal of Bone and Joint Surgery, Incorporated
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