1. Department of Orthopaedic Surgery, Hokkaido University Hospital, N15W7, Sapporo 060-8638, Hokkaido, Japan
2. Department of Orthopaedic Surgery, Eniwa Hospital, 2-1-1 Kogane-Chuo, Eniwa 061-1449, Hokkaido, Japan
3. Division of Systems Science and Informatics, Hokkaido University Graduate School of Information Science and Technology, N14W9, Sapporo 060-0814, Hokkaido, Japan
4. Department of Advanced Medicine for Spine and Spinal Cord Disorders, Faculty of Medicine, Graduate School of Medicine, Hokkaido University, N15W7, Sapporo 060-8638, Hokkaido, Japan