1Department of Orthopaedic Surgery, Institute of Clinical Medicine, University of Tsukuba, 1‐1‐1 Tennoudai, Tsukuba, Ibaraki 305‐8575, Japan
2Department of Anatomy, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Japan
3Yabuki Orthopaedic Clinic, Moriya, Japan