1. Department of Neurosurgery, Soonchunhyang University Bucheon Hospital, Bucheon, Korea.
2. Department of Preventive Medicine, University of Ulsan College of Medicine, Seoul, Korea.
3. Department of Neurosurgery, Gangnam Severance Spine Hospital, Yonsei University College of Medicine, Seoul, Korea.
4. Department of Preventive Medicine, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan, Korea.
5. Department of Neurosurgery, Chonnam National University Hospital and Medical School, Gwangju, Korea.