1 Department of Orthopaedics, Sahlgrenska University Hospital, 431 80, Mölndal, Sweden. jon.karlsson@telia.com.
2 Department of Orthopaedic Surgery and Traumatology, Kantonsspital Baselland (Bruderholz, Liestal, Laufen), Bruderholz, Switzerland.
3 Department of Orthopaedic and Traumatology, City Hospital Brandenburg, Hochstrasse 29, Havel, Brandenburg, 14770, Germany.
4 Department of Orthopaedic Surgery and Bioengineering, Orthopaedic Robotics Laboratory, UPMC Center for Sports Medicine, University of Pittsburgh, 3200 S Water Street, Pittsburgh, PA, 15203, USA.