Similar incidence and implant survival of multiply revised knee arthroplasties in Norway and Denmark: a register study of the Danish and Norwegian Knee Arthroplasty registries from 1998–2021

BACKGROUND AND PURPOSE: The aim of our study was to identify the absolute incidence and implant survival probability of multiply revised knee arthroplasties in Norway and Denmark from 1998 to 2021. METHODS: This was an observational study of primary and revision knee arthroplasties reported prospectively in Norway and Denmark. The nationwide registers in Norway and Denmark were utilized. After identification of all primary procedures reported from 1998 to 2021, revision procedures were identified. Probabilities of implant survival were calculated using Kaplan-Meier methods. A multiply revised knee arthroplasty was defined as at least 3 revisions of a primary knee arthroplasty. RESULTS: The proportion of third revisions was 0.4% in both Denmark (621/159,343) and Norway (404/105,192). The 16-year implant survival of third revisions was 57% (CI 52-62) in Denmark and 54% (CI 48-61) in Norway. No difference in the risk of revision between countries was found for the third revision (HR 1.1, CI 0.7-1.8). CONCLUSION: The incidence of multiply revised knee arthroplasties was not significantly different between Norway and Denmark. The risk and implant survival probability of multiply revised knee arthroplasties was similar in the 2 countries. The results can be used as a benchmark for incidence and prevalence calculations in other countries.