1. Physiotherapy Research Unit, Nuffield Orthopaedic Centre NHS Trust, Windmill Road, Oxford, OX3 7LD, UK.
2. Interdisciplinary Research Centre in Health, Coventry University, Priory Street, Coventry CV1 5FB, UK.
3. Department of Orthopaedics and Trauma, New Royal Infirmary, Edinburgh EH16 4SA, UK.