1. Academic Department of Trauma and Orthopaedics Leeds General Infirmary, Leeds School of Medicine, Leeds University, Great George Street, Leeds LS1 3EX, UK.
2. Princess Elizabeth Orthopaedic Centre, Hip Unit, Royal Devon and Exeter Hospital, Exeter EX2 5DS, UK.
3. Cardio-Thoracic Anaesthetist Unit Blue Cross Hospital, 1 Viziis Street, Thessaloniki 54636, Greece.
4. Institute of Health Sciences, Centre for Epidemiology and Biostatistics, Leeds University, Leeds LS1 3EX, UK.