1. Department of Orthopaedic Surgery, Spine Center, Kyung Hee University College of Medicine, Kyung Hee University Hospital at Gangdong, Seoul, Korea.
2. Department of Orthopaedic Surgery, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
3. Department of Orthopaedic Surgery, Eunpyeong St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.