1. Department of Orthopaedic Surgery, Takikawa Municipal Hospital, Takikawa, Hokkaido, Japan
2. Department of Orthopaedic Surgery, Sapporo Medical University School of Medicine, Sapporo, Hokkaido, Japan
3. Department of Thoracic and Cardiovascular Surgery, Sapporo Medical University School of Medicine, Sapporo, Hokkaido, Japan