1. Department of Neurosurgery, International University of Health and Welfare, School of Medicine, Narita, Japan
2. Department of Neurosurgery, Imari Arita Kyoritsu Hospital, Arita, Japan
3. Department of Neurosurgery, Shiroishi Kyoritsu Hospital, Shiroishi, Japan
4. Department of Orthopaedic Surgery, Faculty of Medicine, Saga University, Saga, Japan.