1. Department of Orthopaedic Surgery, Asahikawa Medical University, Midorigaoka Higashi 2-1-1-1, Asahikawa 078-8510, Japan.
2. Department of Orthopaedic Surgery, Hokkaido University School of Medicine, Kita-15 Nishi-7, Kita-ku, Sapporo 060-8638, Japan.