Received: 21 January 2018
Accepted: 20 April 2018
First Online: 2 May 2018
Ethics approval and consent to participate
: This study was performed with the approval of the institutional research board of Niigata University Medical and Dental Hospital. Written informed consent was obtained from the participants of the normal group. With regard to DDH group, the need for informed consent was waived because of the cross-sectional nature of this study that did not provide an intervention.
: The authors declare that they have no competing interests.
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