Funding for this research was provided by:
Natural Science Foundation of Shandong Province (ZR2017BH04 4)
Received: 18 June 2019
Accepted: 14 August 2019
First Online: 28 August 2019
Ethics approval and consent to participate
: Institutional Review Board approval was not required because the institutional review board of our hospital ethics committee approved this retrospective study, and the requirement for informed consent was waived.
: Not applicable.
: The authors declare that they have no competing interests.