1. Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan
2. Keio Spine Research Group, Tokyo, Japan
3. Department of Orthopaedic Surgery, Saiseikai Central Hospital, Tokyo, Japan
4. Department of Orthopaedic Surgery, Kawasaki Municipal Hospital, Kanagawa, Japan
5. Department of Orthopaedic Surgery, International University of Health and Welfare, Chiba, Japan
6. Department of Orthopaedic Surgery, Sano General Hospital, Tochigi, Japan
7. Department of Orthopaedic Surgery, National Hospital Organization Tokyo Medical Center, Tokyo, Japan
8. Department of Orthopaedic Surgery, Saiseikai Yokohamashi Tobu Hospital, Kanagawa, Japan