1. Godoil Spine and Pain Hospital, Seoul, Korea.
2. Department of Anesthesiology and Pain Medicine, Soonchunhyang Seoul Hospital, Soonchunhyang University College of Medicine, Seoul, Korea.
3. Department of Anesthesiology and Pain Medicine, Soonchunhyang Cheonan Hospital, Soonchunhyang University College of Medicine, Cheonan, Korea.