Schwarzer, A
Holtmann, H
Brugman, M
Meyer, J
Schauerte, C
Zuber, J
Steinemann, D
Schlegelberger, B
Li, Z
Baum, C
Article History
Received: 23 March 2014
Revised: 17 July 2014
Accepted: 6 August 2014
First Online: 22 September 2014
Competing interests
: The authors declare no conflict of interest.