1. Department of Orthopaedic Surgery, Institute of Medicine, University of Tsukuba, Ibaraki 305-8575, Japan
2. Center for Innovating Medicine and Engineering (CIME), University of Tsukuba, Ibaraki 305-0821, Japan
3. Department of Rehabilitation Medicine, Institute of Medicine, University of Tsukuba, Ibaraki 305-8575, Japan
4. Department of Neurosurgery, Institute of Medicine, University of Tsukuba, Ibaraki 305-8575, Japan
5. Faculty of Systems and Information Engineering, University of Tsukuba, Ibaraki 305-8573, Japan