1 Department of Orthopaedic Surgery, Faculty of Medicine, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki, 305-8575, Japan. Electronic address: s-kubota@md.tsukuba.ac.jp.
2 Center for Innovating Medicine and Engineering (CIME), University of Tsukuba Hospital, 1-1-1, Tennodai, Tsukuba, Ibaraki, 305-8575, Japan.
3 Department of Rehabilitation Medicine, University of Tsukuba Hospital, 1-1-1, Tennodai, Tsukuba, Ibaraki, 305-8575, Japan.
4 Department of Orthopaedic Surgery, Faculty of Medicine, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki, 305-8575, Japan.
5 Department of Neurosurgery, Faculty of Medicine, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki, 305-8575, Japan.