Text and Data Mining valid from 2020-01-10
Received: 4 November 2019
Accepted: 8 January 2020
First Online: 10 January 2020
Compliance with ethical standards
: Dr. Takada reports personal fees from Stryker, Medtronic Sofamor Danek, and HOYA, outside the submitted work. Dr. Jinno reports grants and personal fees from Stryker and personal fees from Zimmer Biomet and Depuy Synthes, outside the submitted work. Dr. Miyatake, Dr. Hirao, Dr. Yoshii, and Dr. Okawa declare that they have no conflict of interest.