Introduction: A high degree of registration completeness is necessary in order to obtain unbiased and accurate register-based study results. We investigated the completeness of registration in the national Norwegian Arthroplasty Register (NAR).
Material and methods: Registration completeness for the years 1999-2002 was calculated as a percentage, with the number of joint replacements reported to the NAR as numerator and those reported to the Norwegian Patient Register (NPR) as denominator. While the NAR received information directly from the orthopedic surgeons on a voluntary basis, the NPR, which is mandatory, received information from the electronic administrative patient records of the hospitals.
Results: Registration completeness in the NAR was 97% (97% for primary operations; 101% for revisions). Completeness was 98% (97%; 106%) for hip replacements, and for knee replacements it was 99% (99%; 97%). Hip and knee replacements represented 95% of all operations. However, completeness was poorer for less common joint replacements and poorest for ankle implants (82%; 40%) and wrist implants (52%; 14%). In the NAR, completeness of registration of revisions involving only removal of one or more prosthetic parts was lower than for exchange revisions for all types of joint replacement. For hip implants, 76% of the removal revisions (80% of Girdlestone procedures) were reported, and for knee implants the figure was 62%. According to NPR statistics, removal procedures accounted for 9% of all revisions of hip and knee replacements.
Interpretation: In the NAR, registration completeness of hip and knee replacements was high both for primary operations and exchange revisions. For some of the less common joint replacements, completeness was low and may--if not improved--compromise prosthesis survival studies. The lower registration completeness of removal revisions also needs to be improved.