1. Division of Science for Joint Reconstruction, Graduate School of Medicine; The University of Tokyo; 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8655 Japan
2. Sensory & Motor System Medicine, Faculty of Medicine; The University of Tokyo; 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8655 Japan
3. Department of Materials Engineering, School of Engineering; The University of Tokyo; 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8656 Japan
4. Research Department; KYOCERA Medical Corporation; 3-3-31 Miyahara, Yodogawa-ku Osaka 532-0003 Japan
5. Japan Community Health care Organization; Tokyo Shinjuku Medical Center, Spine Center; 5-1 Tsukudo, Shinjuku-ku Tokyo 162-8543 Japan
6. Materials Research and Development Laboratory; Japan Fine Ceramics Center; 2-4-1 Mutsuno, Atsuta-ku Nagoya 456-8587 Japan