Cochrane in CORR® : Arthroplasty Versus Fusion in Single-level Cervical Degenerative Disc Disease

Importance of the Topic Cervical spondylosis is a common age-related degenerative condition that affects the vertebrae, intervertebral discs, and associated ligaments of the cervical spine [17]. By age 60, 95% of men and 70% of women show radiographic evidence of cervical spondylosis [9], and approximately 8% have MRI evidence of early spinal cord compression [13]. Patients may present with varying combinations of radiculopathy, progressive myelopathy, and axial neck pain [6]. For those who fail to improve with conservative management, decompression through anterior cervical discectomy and fusion is an established and effective surgical option [8]. Following fusion, however, compensatory changes at adjacent spinal levels may lead to accelerated degeneration and recurrence of symptoms. Estimates of the clinical importance and prevalence of adjacent segment disease are highly variable [8]. Cervical intervertebral disc arthroplasty is an alternative procedure intended to prevent adjacent segment disease by maintaining spinal motion. Biomechanical, clinical, and radiographic data suggest its effectiveness, but long-term data are lacking, and the benefits of motion-preservation remain theoretical [1, 4, 7, 10, 18, 19]. This systematic review and meta-analysis sought to determine whether arthroplasty is as least as successful as fusion at relieving pain and preventing neurological decline at short-term followup. Upon Closer Inspection While there were statistically significant differences between groups for several of the primary outcomes (favoring disc replacement), the effect sizes were small, and they probably were not clinically meaningful. Effect sizes this small probably do not justify changes in patient care, particularly where a new technology is concerned, as there are important unanswered questions about costs and longer-term durability with respect to disc arthroplasty that would appear to overshadow these small statistical differences. Minimal Important Differences (MIDs) are the smallest effects that patients perceive as beneficial enough to justify a change in their management, and they can be determined for functional outcome scales [11]. In this review, the authors used MIDs for the Neck Disability Index and the Numerical Rating Scale that were established for patients with neck pain [14]. None of the effect sizes for the primary outcomes exceeded these MIDs. Specific MIDs for patients with radicular pain or myelopathy were not available. Of the nine included studies, eight were industry-sponsored, and outcome assessors, patients, and caregivers were not blinded in any included study. Large studies of new devices involve complex economic and logistic challenges, but industry-sponsorship is believed to bias results towards pro-industry findings [2]. It is possible that the favorable treatment effects for the cervical arthroplasty groups were overestimated in most of the studies. To move forward, researchers must emphasize transparent reporting of study funding, study design, and study management, as well as the processes of manuscript preparation and criteria for authorship [3]. Patients, caregivers, and outcome assessors should be blinded to minimize further bias [12], and surgeon bias can be controlled through expertise-based designs [15]. Take-Home Messages Methodological strengths of this review included a detailed literature search, a thorough assessment of bias among primary articles, and multiple sensitivity analyses to examine internal validity. The authors considered the effects of missing data, study heterogeneity, reporting bias, and clinical differences between subgroups, and they acknowledged the limitations due to short follow-up, small sample sizes, and inconsistent outcome measurements. This study did not include summary estimates for complications or adverse events. Using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system [5], the overall quality of evidence was low to moderate. Fusion and arthroplasty following anterior decompression for symptomatic cervical spondylosis appear to provide equivalent clinical outcomes in the short-term, but future well-designed trials with large sample sizes, rigorous methodology, and long-term followup are warranted. The potential benefits of motion-preservation and reduced adjacent segment disease are of substantial interest to patients and their surgeons, and an evidence-based approach is paramount. Outcomes between specific implants and surgical techniques, as well as between subgroups of patients with varying symptoms of prior treatments should also be examined, and the inclusion of cost-effectiveness analyses will refine the practical implementation of this technology [16].

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