Recurrent inguinal hernia repair: what is the evidence of case series? A meta-analysis and metaregression analysis.

To examine, if case series considered together with observational studies tend to produce similar results as randomized-controlled trials (RCTs), on recurrent hernia repair. A systematic literature review and meta-analysis between 1990 and 2013 revealed 46 nonrandomized studies (NRCTs) and 5 RCTs including 25,730 patients. A direct comparison of the summary estimates between RCTs and NRCTs is presented. Outcomes, within or across studies, were compared. Comparisons of all outcomes in NRCTs and RCTs failed to show statistical significance. Prospective/retrospective cohort studies, case series, and RCTs did not differ significantly in their estimates. Adjusted testing for metaregression disclosed that rerecurrence among NRCTs was independent of the study design. The number of included patients and study setting were independent predictors of outcome. Our proposed methodology for a systematic review could potentially give answers where level I evidence is missing or could be a tool for optimization of a RCT design.