1 Department of Orthopaedics, Sahlgrenska University Hospital, Mölndal, Sweden. jon.karlsson@telia.com.
2 Department of Orthopaedics, Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, 431 80, Gothenburg, Sweden. jon.karlsson@telia.com.
3 Department of Orthopedics and Traumatology, Centre of Joint Replacement, Hospital Brandenburg and "Theodor Fontane" Medical School, 14770, Brandenburg/Havel, Germany.