1. The Shoulder and Elbow Service, The Royal National Orthopaedic Hospital, Stanmore, UK
2. The John Scales Centre for Biomedical Engineering, Institute of Orthopaedics and Musculoskeletal Science, Division of Surgery and Interventional Science, University College London, The Royal National Orthopaedic Hospital, Stanmore, UK
3. Department of Orthopaedic Surgery, University College London Hospital, UK