1. Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Korea.
2. Department of Neurosurgery, Guro Teun Teun Hospital, Seoul, Korea.
3. Department of Neurosurgery, Eulji Hospital, Eulji University College of Medicine, Seoul, Korea.
4. Department of Neurosurgery, Bundang CHA Medical Center, CHA University College of Medicine, Sungnam, Korea.
5. Department of Neurosurgery, The Leon Wiltse Memorial Hospital, Suwon, Korea.
6. Department of Orthopedic Surgery, Kyung Hee University College of Medicine, Seoul, Korea.