1. Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan
2. Department of Spine Surgery, Beijing Jishuitan Hospital, the 4th Teaching Hospital of Peking University, Beijing, China
3. Department of Neurosurgery, Yonsei University, Seoul, Korea
4. Department of Orthopaedics and Traumatology, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong