1Department of Orthopaedic Surgery, University of Tokyo, Japan
2Clinical Bioengineering, V.A. Medical Center, West Roxbury, MA and Orthopaedic Biomechanics, Brigham and Womens Hospital, Boston, MA, U.S.A.
3Hiji Kodama Hospital, Oita, Japan
4Massachusetts institute of Technology, Cambridge, MA, U.S.A.