1. Department of Neurosurgery, National Health Insurance Service Ilsan Hospital, Goyang, Korea.
2. Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Korea.
3. Department of Policy Research Affairs, National Health Insurance Service Ilsan Hospital, Goyang, Korea.
4. Department of Neurosurgery, Spine and Spinal Cord Institute, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.