Linda C Li1, Philip J van der Wees2. 1. L.C. Li, PT, PhD, is a guest co-editor of this special series. She is Associate Professor, Harold Robinson/Arthritis Society Chair in Arthritic Diseases, Canada Research Chair in Patient-oriented Knowledge Translation, Department of Physical Therapy, University of British Columbia, Vancouver, BC; and Senior Scientist, Arthritis Research Canada, Richmond, BC, Canada. 2. P.J. van der Wees, PT, PhD, is a guest co-editor of this special series and a PTJ editorial board member. He is Senior Researcher, Scientific Institute for Quality of Healthcare, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, the Netherlands.