1. The Swedish Hip Arthroplasty Register, Department of Orthopedics, Institute of Surgical Sciences, Sahlgrenska University Hospital, University of Gothenburg, Sweden
2. The Norwegian Arthroplasty Register, Department of Orthopedic Surgery, Haukeland University Hospital, Bergen
3. Department of Surgical Sciences, University of Bergen, Norway
4. The Danish Hip Arthroplasty Register and Department of Orthopedic Surgery, Clinical Institute, Odense University Hospital, Odense
5. The Danish Hip Arthroplasty Register and Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark