Assessing the Effects of Publication Bias on Reported Outcomes of Cervical Disc Replacement and Anterior Cervical Discectomy and Fusion: A Meta-Epidemiological Study.

To date, there have been several clinical trials as well as observational studies that have compared the outcomes of different cervical disc replacement (CDR) devices with anterior cervical disc replacement and fusion (ACDF). While the results of these studies have provided sufficient evidence for the safety of CDR, there is still a lack of consensus in terms of longer term outcomes with studies providing equivocal results for the two procedures. In the current study, we utilized a novel methodology, a meta-epidemiological study, to investigate the impact of study characteristics on the observed effects in the published literature on CDR and ACDF.Data was abstracted from available meta-analyses regarding author, study author, year, intervention events, control events, sample size, as well as year and geographical location of each study within the meta-analyses. We grouped the studies based on median year of publication as well as the region of the submitting author(s). Odds ratios (OR), their 95% confidence intervals (95% CI), and their standard errors (SE) of individual studies were calculated based on the number of events and sample size for each arm (ACDF or CDR). Further, results of outcomes from individual studies were pooled and a meta-analysis was conducted. Ratio of odds ratio (ROR) was used to assess the impact of each of these factors on estimates of the study for CDR vs ACDF.A total of 13 meta-analyses were analyzed after exclusions. Using the results from 10 meta-analyses, we found that studies published before 2012 reported significantly lower odds of a reoperation after CDR (vs ACDF), compared to studies published after (ROR 0.51, 95% CI 0.38-0.67, p<0.001). We did not observe a significant impact of study year on difference in estimates between CDR and ACDF for adjacent segment disease (ROR = 0.99, 95% CI: 0.64-1.55, p = 0.465). Finally, the region of submitting author was also found to have no impact on results of published studies.These results indicate that there may be a publication bias with regards to the year of publication, with earlier studies reporting lower reoperation rates for CDR in comparison to ACDF.