1. Kadoorie Trauma Research Unit Nuffield Department of Orthopaedic Rheumatology and Musculoskeletal Sciences, University of Oxford, John Radcliffe Hospital, Headley Way, Oxford OX3 9DU, UK.
2. The Botnar Research Centre Institute of Musculoskeletal Sciences Nuffield Department of Orthopaedic Surgery, University of Oxford, Nuffield Orthopaedic Centre, Windmill Road, Oxford OX3 7LD, UK.
3. Department of Engineering Science Institute of Biomedical Engineering, Old Road Campus Research Building, University of Oxford, Headington, Oxford OX3 7DQ, UK.