1. Department of Orthopedic Surgery, Institute of Medicine, University of Tsukuba, Tsukuba 305-8571, Ibaraki, Japan
2. Department of Orthopedic Surgery, Kasumigaura Medical Hospital, Tsuchiura 300-8585, Ibaraki, Japan
3. Department of Orthopedic Surgery, Mito Medical Center, Ibaraki 311-3193, Ibaraki, Japan
4. Department of Orthopedic Surgery, National Center of Neurology and Psychiatry, Kodaira 187-8551, Tokyo, Japan
5. Department of Orthopedic Surgery, Tokyo Medical University Ibaraki Medical Center, Ami 300-0395, Ibaraki, Japan