Background and purpose The reproducibility of results and potential confounders in sample-based studies is important to consider in the assessment of studies. Comprehensive arthroplasty registers could serve as a reference dataset for comparative analyses. We analyzed an implant that is frequently used worldwide, the Oxford unicompartmental knee replacement, in order to identify potential confounders inherent in the datasets and to evaluate the outcome achieved with this implant.Methods We performed a structured literature review of the data published on the revision rate of the Oxford medial unicompartmental arthroplasty. Both clinical follow-up studies and worldwide registry data were included. Confidence intervals were calculated to determine the statistical significance of differences.Results A substantial proportion of the published data (52–68% depending on the method of calculation) is derived from studies involving participation of the institution that developed the implant. The results published by this group show a statistically significant deviation from the reference datasets from registers or independent studies. Data from the developing hospital show mean revision rates that are 4 times lower than those based on worldwide register data, and 3 times lower than the ones quoted in independent studies. On average, the data published in independent studies are reproducible in registry data.Interpretation A conventional meta-analysis of clinical studies is substantially affected by the influence of the developing hospital, and is therefore subject to bias. For assessment of the outcome of implants, registry data are superior and, in terms of reference data for the detection of potential bias factors in the literature, could make an essential contribution to meta-analyses.

Purpose Implant fractures after total hip arthroplasty (THA) are considered as rare in clinical practice. Nevertheless they are relevant complications for patients, physicians, and the public health system leading to high socioeconomic burdens. The aim of this study was to assess the incidence of fractures after THAs in a comparative analysis of clinical studies and worldwide arthroplasty register datasets. Methods We calculated the pooled incidence of revision operations after fractures of THAs in a comparison of clinical studies published in Medline-listed journals and annual reports of worldwide arthroplasty registers in a structured literature analysis based on a standardised methodology. Results Included clinical studies (sample-based datasets) were mono-centre trials comprising a cumulative number of approximately 70,000 primary implantations whereas worldwide national arthroplasty register datasets referred to 733,000 primary implantations, i.e. approximately ten times as many as samplebased datasets. In general, sample-based datasets presented higher revision rates than register datasets with a maximum deviation of a 14.5 ratio for ceramic heads, respectively. The incidence of implant fractures in total hip arthroplasty in pooled worldwide arthroplasty register datasets is 304 fractures per 100,000 implants. In other words, one out of 323 patients has to undergo revision surgery due to an implant fracture after THA in their lifetime. Conclusions Implant fractures in total hip arthroplasty occur in a relevant number of patients. The authors believe that comprehensive arthroplasty register datasets allow more general evaluations and conclusions on that topic in contrast to clinical studies.