Article History
Received: 5 June 2018
First Online: 17 October 2018
Compliance with ethical standards
:
: This study was approved by the institutional review board of the authors' institutions. All procedures performed involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
: Informed consent was obtained from all participants included in the study.
: The Department to which the first author belongs received funding for operating costs from Saku Central Hospital of the Nagano Prefectural Federation of Agricultural Cooperatives for Health and Welfare, Medtronic Sofamor Danek Co., Ltd., Stryker Japan Co. Ltd., HOYA Technosurgical Co., Ltd., and A-Z Co. Ltd. All other authors declare that they have no conflicts of interest.