1. Department of Orthopaedics, Lund University Hospital, SE-221 85, Lund, Sweden.
2. Department of Orthopaedics, Karolinska Hospital, SE-171 76, Stockholm, Sweden.
3. Department of Orthopaedics, Haukeland University Hospital, NO-5021, Bergen, Norway.
4. Department of Orthopaedics and Traumatology, Helsinki University, Central Hospital, FI-00029, Helsinki, Finland.
5. Department of Orthopaedics, Sahlgrenska Hospital, SE-413 45, Göteborg, Sweden.
6. Department of Orthopaedic Surgery, århus University Hospital, DK-8000 århus C, Denmark.
7. Department of Surgery/Orthopaedics, Rikshospitalet University Hospital, Montbello, NO-0310, Oslo 3, Norway.