Ragnum, H B
Vlatkovic, L
Lie, A K
Axcrona, K
Julin, C H
Frikstad, K M
Hole, K H
Seierstad, T
Lyng, H
Article History
Received: 30 July 2014
Revised: 15 October 2014
Accepted: 4 November 2014
First Online: 2 December 2014
Competing interests
: The authors declare no conflict of interest.