Validation of periprosthetic joint infection after total knee arthroplasty: a cohort study on 423 cases from the Norwegian Arthroplasty Register

BACKGROUND AND PURPOSE: Periprosthetic joint infection (PJI) is a serious complication following total knee arthroplasty (TKA). Accurate reporting is essential for quality development and research based on data in the Norwegian Arthroplasty Register (NAR). Our study aimed to validate Norwegian orthopedic surgeons' reporting of reoperations for PJI. METHODS: We assessed detailed clinical, biochemical, and microbiological data on 423 patients reported to the NAR for reoperations after primary TKA performed in Western Norway in the period from 2010 to 2023. We used the Musculoskeletal Infection Society (MSIS) definition of PJI. For each cause of reoperation (including causes that could mimic PJI, such as aseptic loosening, prolonged wound drainage, and pain alone), we determined the sensitivity, specificity, negative and positive predictive values, and accuracy. RESULTS: Of 423 reoperations, 170 were reported reoperations due to PJI. After validation, 94% (159 of 170) were confirmed to be due to PJI. Furthermore, 5% (13 of 253) of cases reported as reoperated due to causes other than deep infection were validated as PJI. The sensitivity, specificity, and accuracy for PJI reporting were 92%, 96%, and 94%, respectively. Accuracy for aseptic loosening, prolonged wound drainage, and pain alone was 97%, 94%, and 98%, respectively. CONCLUSION: The accuracy of reporting of reoperations due to PJI is high, thereby affirming the quality of reoperation data concerning PJI submitted to the NAR. Our findings support the use of NAR data in quality development and research.