1. Department of Orthopaedic Surgery, Clinical Orthopaedic Research Hvidovre (CORH), Copenhagen University Hospital Hvidovre, Denmark;;
2. Department of Clinical Epidemiology, Aarhus University Hospital, Denmark;
3. Department of Orthopaedic Surgery, Vejle Hospital, Denmark;
4. Nuffield Department of Orthopaedic Surgery, Rheumatology and Musculoskeletal Science, Nuffield Orthopaedic Centre, University of Oxford, UK