1. Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Sahlgrenska University Hospital Mölndal, SE-431 80, Mölndal, Sweden.
2. Department of Orthopaedics, Malmö University Hospital, Lund University, SE-20502, Malmö, Sweden.
3. Department of Orthopaedics, Massachusetts General Hospital, 55 Fruit Street, GR1126 Boston, Massachusetts, 02114, USA.