1. The London Hip Unit, 4th Floor, 30 Devonshire Street, London W1G 6PU, UK.
2. Department of Biomedical Engineering, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore HA7 4LP, UK.
3. MIS Laboratory, Department of Orthopaedic Surgery, NYU Medical Center, Hospital for Joint Disease, 301 East 17th Street, Manhattan, New York, 10003, USA.