1. Department of Rehabilitation Medicine, School of Medicine, Keio University, Tokyo 160-8582, Japan
2. Department of Rehabilitation Medicine, Faculty of Medicine, Kyorin University, Tokyo 181-8611, Japan
3. Division of Microscopic Anatomy, Graduate School of Medical and Dental Sciences, Niigata University, Niigata 951-8510, Japan
4. Department of Orthopaedic Surgery, School of Medicine, Keio University, Tokyo 160-8582, Japan
5. Department of Physiology, School of Medicine, Keio University, Tokyo 160-8582, Japan