1. Swedish Hip Arthroplasty Register, Gothenburg, Sweden;
2. Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Sweden;
3. Department of Orthopaedics, Hywel Dda University Healthboard, Prince Philip Hospital, Llanelli, UK;
4. Section of Orthopaedic Surgery, Department of Surgical Sciences, Uppsala University Hospital, Uppsala, Sweden