1. Department of Neurosurgery, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea;
2. Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Korea;
3. Department of Neurosurgery, Spine Center, Hallym University Sacred Heart Hospital, Seoul, Korea;
4. Department of Neurosurgery, Keimyung University Dongsan Medical Center, Daegu, Korea