Validation of data in the Norwegian Arthroplasty Register and the Norwegian Patient Register : 5,134 primary total hip arthroplasties and revisions operated at a single hospital between 1987 and 2003

Background The usefulness of a national medical register relies on the completeness and quality of the data reported. The data recorded must therefore be validated to prevent systematic errors, which can cause bias in reports and study conclusions. Patients and methods We compared the number of hip replacements reported to the Norwegian Arthroplasty Register (NAR), 1987-2003, and to the Norwegian Patient Register (NPR), 1999-2002, with data recorded at a local hospital. The date of operation and the index hip were further validated to find inaccurately recorded data in the NAR. Kaplan-Meier estimated survival curves were compared to evaluate the possible influence of missing data. Results Of 5,134 operations performed at a local hospital, 19 (0.4%) had not been reported to the NAR. Completeness of registration was poorer for revisions (1.2%) than for primary operations (0.2%). Among 86 Girdlestone revisions (removal of the prosthesis only), 9 (11%) had not been reported to the NAR. Missing data on revisions, however, had only a minor influence on survival analyses. The date of the operation had been recorded incorrectly in 56 cases (1.1%), and the index hip in 12 cases (0.2%). The surgeon was responsible for 85% of these errors. Comparisons with data reported to the NPR, 1999-2002, showed that 3.4% of operations at the local hospital had not been reported to the NPR. Interpretation Only 0.4% of the data from a local hospital was missing in the NAR, as opposed to the NPR where 3.4% was missing. The information recorded in the NAR appears to have been valid and reliable throughout the entire period, and provides an excellent basis for clinically relevant information regarding total hip arthroplasty.