Pain Outcomes in Patients after Artificial Disc Replacement versus Fusion in the Cervical Spine: A Systematic Review of Systematic Reviews

Background: Pain is a major complaint for patients with cervical disc disease and is one of the reasons for surgery. Cervical artificial disc replacement (C-ADR) has been introduced in 2002 to offer an alternative to anterior cervical discectomy and fusion (ACDF) to treat disc disease in the cervical spine and to reduce dysphagia, dislodgement or fracture in the affected segment or an increase motion at the adjacent levels of the cervical spine. Several studies and reviews attempted in the last decade to compare the two procedures head to head and to evaluate whether the new procedure lead to less complications, better clinical outcomes and more patients’ satisfaction. However, less attention was paid to pain outcomes in these studies. Aim: To evaluate the pain outcomes resulted from C-ADR in comparison to ACDF by reviewing the evidence presented in the systematic reviews of randomized clinical trails and other studies containing clinical data. Methods: A combination of the following keywords was used in the search for systematic reviews in [Medline via Ovid, Embase, Cochrane Database of Systematic Reviews, Google scholar]: (total disc replacement, prosthesis, implantation, diskectomy, arthroplasty) and (cervical vertebrae, cervical spine, spine) and (pain, disability, quality of life) and (systematic reviews, reviews, meta-analysis). The initial search was conducted on the 18 August 2013 and then updated on 02/12/2015. Two authors screened the results of the search independently. For the article to be selected for further consideration it has to be a systematic review and/or meta-analysis of trials that attempted to compare between the two interventions at the cervical region in which the pain relief was a primary or a secondary outcome. Results: The electronic search produced 881 hits of which 145 were duplicates. Twenty more articles were identified through manual search. Initial screening of the abstracts resulted in selection of 68 articles for further evaluation. The final judgement of the two reviewers was to include 10 systematic reviews and/or metaanalyses in this overview. The number of randomised trials reviewed by the selected reviews varies from 2 to 27. Other discrepancies between the reviews included: the follow up period, the outcomes considered and reporting of heterogeneity or publication bias of the included studies. Eight reviews and meta-analyses concluded that overall C-ADR is more effective and probably superior to ACDF specifically in neurological success, low rate of secondary operation and most pain outcomes. One meta-analysis concluded that ACDF is associated with shorter operative time and less blood loss compared to C-ADR. However, a Cochrane review critically evaluated the differences between the clinical outcomes of the two interventions and while confirmed that C-ADR superiority may be statistically significant in many of these outcomes, the differences between C-ADR and ACDF is too small. This was also evident in all meta-analyses evaluated here. Conclusion: C-ADF may be superior, or at least equivalent, to ACDF in most clinical and patients’ outcomes but the effect size of the difference is small and more time and research is needed to reach a definitive conclusion. A robust systematic reviewing is also recommended.