1 Department of Orthopaedic Surgery, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan.
2 Department of Orthopaedic Surgery and Sports Medicine, Tsukuba University Hospital Mito Clinical Education and Training Center, Mito Kyodo General Hospital, Mito, Japan.
3 Department of Orthopaedic Surgery, Ibaraki Prefectural University of Health Sciences, Ami, Japan.