1. Department of Orthopaedic Surgery, Keio University School of Medicine , Shinjuku-ku, Tokyo , Japan
2. Department of Physiology, Keio University School of Medicine , Shinjuku-ku, Tokyo , Japan
3. Department of Rehabilitation Medicine, Keio University School of Medicine , Shinjuku-ku, Tokyo , Japan
4. Division of Microscopic Anatomy, Graduate School of Medical and Dental Sciences, Niigata University , Niigata City, Niigata , Japan
5. Electron Microscope Laboratory, Keio University School of Medicine , Shinjuku-ku, Tokyo , Japan