1. Department of Orthopedic Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan
2. Department of Orthopedic Surgery, Kyoto Prefectural University of Medicine, 465 Kajii-cho, Kamigyo-ku, Kyoto 602-8566, Japan
3. Sapporo Endoscopic Spine Surgery Clinic, 1-13, North-16, East-16, Higashi-ku, Sapporo 065-0016, Japan
4. Sapporo Medical Research, 1-20-1501, Kita13 Higashi2, Hidashi-ku, Sapporo 065-0013, Japan