Ückert, S
Sonnenberg, J
Sonnenberg, J E
Kauffels, W
Albrecht, K
Kuczyk, M A
Hedlund, P
Article History
Received: 4 March 2016
Revised: 5 December 2016
Accepted: 13 February 2017
First Online: 13 April 2017
Competing interests
: The authors declare no conflict of interest.