1. Department of Orthopaedic Surgery, Hokkaido Spinal Cord Injury Center, Bibai, Hokkaido, Japan
2. Department of Orthopaedic Surgery, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, Japan
3. Department of Orthopaedic Surgery, Hokkaido University Faculty of Medicine and Graduate School of Medicine, Sapporo, Hokkaido, Japan