1. Department of Clinical Epidemiology
2. Department of Orthopaedic Surgery, Aarhus University Hospital, Tage Hansens Gade 2, 8000 Aarhus C, Denmark.
3. Department of Orthopaedic Surgery, Odense University Hospital, Sdr. Boulevard 30, 5000 Odense, Denmark.
4. Department of Orthopaedic Surgery, Aarhus University Hospital, Ole Worms Alle 1150, 8000 Aarhus C, Denmark.