Department of Orthopaedics, Sahlgrenska University Hospital, Gothenburg, Sweden. Department of Orthopaedics, University of Gothenburg, Sahlgrenska Academy, Institute of Clinical Sciences, Gothenburg, Sweden. Department of Clinical Medicine, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark. Department of Orthopaedic Surgery, Copenhagen University Hospital, Hvidovre, Denmark. Harris Orthopaedic Laboratory, Massachusetts General Hospital, Boston, Massachusetts, USA. Harvard Medical School, Harvard University, Boston, Massachusetts, USA.