1. Department of Neurosurgery, Guro Teun Teun Hospital, Seoul, Korea.
2. Department of Neurosurgery, Spine and Spinal Cord Research Institute, Spine Research Laboratory, Yonsei University College of Medicine, Seoul, Korea.
3. Department of Neurosurgery, Kangbuk Samsung Hospital, Sungkyunkwan University College of Medicine, Seoul, Korea.
4. Department of Neurosurgery, Spine Center, Hallym University Sacred Heart Hospital, Seoul, Korea.