1. Lovisenberg Diakonale Hospital, Oslo;
2. The Norwegian Arthroplasty Register, Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen;
3. Department of Clinical Medicine, Institute of Medicine and Dentistry, University of Bergen, Bergen;
4. Haugesund Hospital, Haugesund;
5. Orthopaedic Research Center, Trondheim University Hospital, Trondheim;
6. Department of Orthopaedics, Oslo University Hospital, Ullevål, Oslo, Norway;
7. Department of Surgical and Perioperative Sciences, Orthopaedics, Umeå University, Umeå, Sweden