Article History
Received: 13 March 2018
Accepted: 4 October 2018
First Online: 11 October 2018
Compliance with ethical standards
:
: Herman Frima, Roderick M. Houwert and Christoph Sommer declare that they have no conflict of interest.
: All procedures performed in studies 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. This study was approved by the Kantonale Ethikkommision Zürich.