Tanujan Thangarajah1, Simon Lambert2. 1. John Scales Centre for Biomedical Engineering, Institute of Orthopaedics and Musculoskeletal Science, Division of Surgery and Interventional Science, University College London, Royal National Orthopaedic Hospital, Stanmore, HA7 4LP, UK; 2. Shoulder and Elbow Service, Royal National Orthopaedic Hospital, Stanmore, UK.