- Correspondence to Dr J Chu, Department of Physical Medicine and Rehabilitation, Perelman School of Medicine, University of Pennsylvania, Ardmore, PA 19003-2321, USA;
- Received 8 August 2016
- Revised 10 December 2016
- Accepted 7 March 2017
- Published in print 1 April 2017.
- Published online 25 April 2017.
- Published first 24 March 2017.
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