1. Department of Orthopedic Surgery, Tokyo Medical University Ibaraki Medical Center, Ami 300-0395, Japan
2. Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Tsukuba 305-8577, Japan
3. Department of Orthopaedic Surgery, Tsukuba Medical Center Hospital, 1-3-1, Amakubo, Tsukuba 305-8576, Japan
4. Department of Orthopedic Surgery, Kikkoman General Hospital, Noda 278-0005, Japan
5. Department of Orthopaedic Surgery, National Hospital Organization Mito Medical Center, Ibaraki 311-3193, Japan