Department of Neurosurgery, Seoul St Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea. Department of Neurosurgery, Chungdam Wooridul Spine Hospital, Seoul, Korea. Department of Neurosurgery, Wiltse Memorial Hospital, Anyang, Korea. Department of Orthopaedic Surgery, Chungdam Wooridul Spine Hospital, Seoul, Korea. Spine Center and Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Bundang Hospital, Seongnam, Korea. Department of Orthopedic Surgery, Spine Center, Kangnam Sacred Heart Hospital, Hallym University College of Medicine, Seoul, Korea. Department of Neurosurgery, Daejeon St Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.