Homogeneity in prediction of survival probabilities for subcategories of hipprosthesis data: the Nordic Arthroplasty Register Association, 2000–2013

Abstract

Christoffer Bartz-Johannessen,1 Ove Furnes,1,2 Anne Marie Fenstad,1 Stein Atle Lie,1,3 Alma Becic Pedersen,4,5 Søren Overgaard,5,6 Johan Kärrholm,7 Henrik Malchau,7–9 Keijo Mäkelä,10,11 Antti Eskelinen,11,12 Jeremy M Wilkinson131Norwegian Arthroplasty Register, Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway; 2Department of Clinical Medicine, University of Bergen, Bergen, Norway; 3Department of Clinical Dentistry, University of Bergen, Bergen, Norway; 4Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark; 5Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark; 6Department of Orthopaedic Surgery and Traumatology Odense University Hospital and Institute of Clinical Research, University of Southern Denmark, Odense Denmark; 7Swedish Hip Arthroplasty Register, Department of Orthopaedics, Institute of Surgical Sciences, Sahlgrenska University Hospital, Gothenburg, Sweden; 8Harris Orthopaedic Laboratory, Massachusetts General Hospital, Boston, USA; 9Department of Orthopaedic Surgery, Harvard Medical School, Boston, MA, USA; 10Department of Orthopaedics and Traumatology, Turku University Hospital, Turku, Finland; 11Finnish Arthroplasty Register, Finnish Institute of Health, Helsinki, Finland; 12Department of Orthopaedics Surgery, Coxa Hospital for Joint Replacement, Tampere, Finland; 13Department of Oncology and Metabolism, University of Sheffield, Sheffield, UKIntroduction: The four countries in the Nordic Arthroplasty Register Association (NARA) share geographic proximity, culture, and ethnicity. Pooling data from different sources in order to obtain higher precision and accuracy of survival-probability estimates is appealing. Nevertheless, survival probabilities of hip replacements vary between the countries. As such, risk prediction for individual patients within countries may be problematic if data are merged. In this study, our primary question was to address when data merging for estimating prosthesis survival in subcategories of patients is advantageous for survival prediction of individual patients, and at what sample sizes this may be advised.Methods: Patients undergoing total hip replacements for osteoarthritis between January 1, 2000 and December 31, 2013 in the four Nordic countries were studied. A total of 184,507 patients were stratified into 360 patient subcategories based on country, age-group, sex, fixation, head size, and articulation. For each patient category, we determined the sample size needed from a single country to obtain a more accurate and precise estimate of prosthesis-survival probability at 5 and 10 years compared to an estimate using data from all countries. The comparison was done using mean-square error.Results: We found large variations in the sample size needed, ranging from 40 to 2,060 hips, before an estimate from a single Nordic country was more accurate and precise than estimates based on the NARA data.Conclusion: Using pooled survival-probability estimates for individual risk prediction may be imprecise if there is heterogeneity in the pooled data sources. By applying mean-square error, we demonstrate that for small sample sizes, applying the larger NARA database may provide a more accurate and precise estimate; however, this effect is not consistent and varies with the characteristics of the subcategory.Keywords: hip replacement, arthroplasty registry, merging data sets, variance, accuracy, precision

Keywords

• The Nordic Arthroplasty Register Association
• hip replacement
• risk prediction
• survival probabilities