Existing data sources for clinical epidemiology: The Danish Knee Arthroplasty Register

Alma B Pedersen¹, Frank Mehnert¹, Anders Odgaard², Henrik M Schrøder<sup>3

1</sup>Department of Clinical Epidemiology, ²Department of Orthopedics, Aarhus University Hospital, Aarhus, ³Department of Orthopedics, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

Purpose: We described the settings, organization, content, and data quality of the Danish Knee Arthroplasty Register (DKR), as well as the incidence and the first results of the knee replacement procedures captured by the DKR. Our aim was to draw researchers' attention to the DKR and its potential use in clinical epidemiological research.
Patients and methods: The DKR has collected data on all knee replacement procedures performed in Denmark since 1997. The validity of the register was compared with the Danish National Registry of Patients (DNRP). Incidence rate was calculated per 100,000 inhabitants. Implant survival was estimated by Kaplan–Meier method. Cox regression analyses were used to estimate the relative risk (RR) for revision with a 95% confidence interval (CI).
Results: A total of 62,586 primary knee arthroplasties and 6,683 revisions were registered in the DKR between January 1, 1997 and December 31, 2010. More than 90% of the private and public hospitals performing knee replacement surgery in Denmark have entered data to the DKR. Registration completeness of primary procedures and revisions has increased since the DKR initiation and was 88% in 2010 for both procedures, compared with registration in the DNRP. For primary knee arthroplasties, the annual incidence rate increased from 35.8 in 1997 to 155.2 in 2010 per 100,000 inhabitants. Incidence was higher in females than in males during the entire study period, and increased with age for both sexes. The overall implant survival after 14 years was 89% irrespective of diagnosis for surgery. Male patients had higher revision risk than females, and revision risk decreased with increasing age. Risk for any revision was higher for uncemented implants (RR = 1.48; 95% CI: 1.32–1.66), and lower for hybrid implants (RR = 0.84; 95% CI: 0.75–0.95) compared to cemented implants. Implant survival did not improve but remained the same throughout the study period when comparing patients operated in the periods 1997–2000 versus 2001–2003, 2004–2006, and 2007–2010.
Conclusion: The DKR is a valuable tool for quality monitoring and research in knee arthroplasty surgery due to the high quality and completeness of prospective, routinely collected data. Large population-based epidemiological studies can be performed in order to study trends as well as risk factors for poor clinical outcome following knee arthroplasty surgery.

Keywords: knee replacement, register, incidence, completeness, implant survival