1. The Norwegian Arthroplasty Register, Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen - Norway
2. Department of Orthopaedics, Lund University, Skåne University Hospital, Malmö - Sweden
3. The Swedish Hip Arthroplasty Register, Registercentrum VGR, Gothenburg - Sweden
4. Department of Clinical Medicine, University of Bergen, Bergen - Norway
5. Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, Gothenburg - Sweden