1 Robert L. and Mary Ellenburg Professor of Surgery, Department of Orthopaedic Surgery and (by Courtesy) Bioengineering, Stanford University Medical Center Outpatient Center, 450 Broadway St., M/C 6342, Redwood City, CA 94063, USA.
2 Department of Orthopaedics and Traumatology, Innovative Orthopaedic Biomaterial and Drug Translational Research Laboratory, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong, China.