Acknowledgements
We thank Ms. Tan Bee Yee, the head of the Department of Physiotherapy, Singapore General Hospital, for supporting this study. We also thank Ms. Tiffany Ang, Ms. Alicia Ang, and Ms. Yinjie Lee for their research assistance. Finally, we thank the orthopaedic surgeons from the Singapore General Hospital for allowing us access to their patients. This work is supported by a Singhealth Foundation grant (SHF/FG398S/2009).