1 Musculoskeletal Research Unit, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol BS10 5NB, UK. Electronic address: celia.gregson@bristol.ac.uk.
2 Department of Geriatrics, Division of Internal Medicine, School of Clinical Medicine, College of Health Science, University of Kwa-Zulu Natal, Durban, South Africa.
3 MRC/Wits Developmental Pathways for Health Research Unit, Department of Paediatrics, School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
4 Division of Orthopaedic Surgery, Department of Surgery, School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa; Division of Orthopaedic Surgery, Charlotte Maxeke Johannesburg Academic Hospital, Johannesburg, South Africa.
5 Clinical Research Department, London School of Hygiene and Tropical Medicine, London, UK; Biomedical Research and Training Institute, Harare, Zimbabwe.
6 Medical Research Council Lifecourse Epidemiology Unit, University of Southampton, Southampton, UK; Medical Research Council Elsie Widdowson Laboratory, Cambridge, UK.