1. International Centre for Evidence in Disability, London School of Hygiene & Tropical Medicine, Keppel Street, London, UK
2. Witswatersrand University, 1 Jan Smuts Avenue, Braamfontein 2000, Johannesburg, South Africa
3. Nuffield Department of Orthopaedics Rheumatology and Musculoskeletal Science, University of Oxford, Windmill Road, Headington, Oxford, UK