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