1. Department of Orthopaedic Surgery, Stanford University School of Medicine, Stanford, CA 94063, USA
2. Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan
3. Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Hong Kong
4. Department of Bioengineering, Stanford University School of Medicine, Stanford, CA 94305, USA