Kirsch, M
Götz, A
Halter, J P
Schanz, U
Stussi, G
Dobbels, F
De Geest, S
Article History
Received: 13 March 2014
Revised: 12 May 2014
Accepted: 23 May 2014
First Online: 21 July 2014
Competing interests
: The authors declare no conflict of interest.