1. Department of Trauma and Orthopaedic Surgery, Queens Medical Centre, University Hospital, Nottingham NG7 2UH, UK.
2. Department of Orthopaedic Surgery, Frenchay Hospital, Beckspool Road, Bristol BS16 1LE, UK.
3. Department of Trauma and Orthopaedic Surgery, Bristol Royal Infirmary, Marlborough Street, Bristol BS2 8HW, UK.
4. Department of Anatomy, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.