Poor agreement between data from the National Patient Registry and the Danish Patient Insurance Association.

INTRODUCTION Septic arthritis after knee arthroscopy requires in-patient treatment and should thus be reported to the National Patient Registry (NPR). It also meets the requirements for financial compensation if claimed to the Danish Patient Insurance Association (DPIA). The aim of this study was to assess data from the two independent data sources, the NPR and DPIA, with a view to comparing the registration of septic arthritis after knee arthroscopy. MATERIAL AND METHODS This was a retrospective study assessing two three-year periods. From the NPR, we initially received all contacts coded as arthroscopic knee surgery. A second NPR query was made for patients found in the first query who had had a hospital contact within 30 days postoperatively with codes indicating septic arthritis (450 patients). Correspondingly, the DPIA files of patients claiming an infection following knee arthroscopy were searched to identify those (157 patients) with post-arthroscopic septic arthritis. RESULTS We found poor agreement between the 450 patients in the second NPR data extraction and the 157 verified patients from the DPIA. Only 105 patients from DPIA were found in the NPR, while 52 patients in the DPIA were not returned as part of the second NPR data extraction. CONCLUSION Coding of infections after arthroscopy in the NPR is inconsistent and incomplete. An underreporting of septic arthritis to the DPIA might exist.