1. Department of Orthopaedic Surgery; Yamagata University Faculty of Medicine; Yamagata Japan
2. Department of Clinical Medicine; Yamagata Saisei Hospital; Yamagata Japan
3. Department of Orthopaedic Surgery; Stanford University School of Medicine; California 94063
4. Department of Medicine; Biomedicum Helsinki, University of Helsinki; Helsinki FIN-00014 HY Finland