1. Department of Orthopaedic Surgery, Izumi Municipal Hospital, 4-10-10 Fuchu Izumi City, Osaka 594-0071, Japan
2. Department of Neurosurgery, Izumi Municipal Hospital, 4-10-10 Fuchu Izumi City, Osaka 594-0071, Japan
3. Department of Orthopaedic Surgery, Osaka City University Graduate School of Medicine, 1-5-7 Asahi Abeno, Osaka 545-0051, Japan