1. Department of Orthopedic Surgery, Dongguk University Ilsan Hospital, Goyang-si;
2. Department of Orthopedic Surgery, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung-si; and
3. Departments of Neurosurgery and
4. Orthopedic Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea