1. Department of Neurosurgery, Spine Center, Kyung Hee University Hospital at Gangdong, Seoul, Korea.
2. Department of Orthopedic Surgery, Spine Center, Kyung Hee University Hospital at Gangdong, Seoul, Korea.
3. Department of Orthopedic Surgery, Chunchon Sacred Heart Hospital, Hallym University College of Medicine, Chuncheon, Korea.