Article History
Received: 20 September 2016
Accepted: 29 May 2017
First Online: 2 June 2017
Compliance with ethical standards
:
: M. van Basten Batenburg, I. B. Houben and T.J. Blokhuis declare that they have no conflict of interest.
: Since this study solely used retrospective data, neither humans nor animals participated actively in the study.
: The retrieval of data was covered by the general institutional review board (IRB) approval for data analysis in our institution.