1. Department of Neurosurgery, Spine Center, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
2. Department of Neurosurgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
3. Department of Orthopedic Surgery, Wooridul Spine Hospital, Seoul, Korea.
4. Department of Neurosurgery, College of Medicine, Inha University, Incheon, Korea.
5. Department of Orthopaedic Surgery, Spine Service, Columbia University College of Physicians and Surgeons, New York, NY, USA.