Received: 15 October 2017
Accepted: 1 March 2018
First Online: 12 March 2018
Ethics approval and consent to participate
: The study was approved by the responsible local ethical committee of the Landesärztekammer Hess, Frankfurt, Germany (file number FF 135/2013). The committee decided that additional informed consent was not required for this retrospective analysis.
: Not applicable.
: The authors declare that they have no competing interests.
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