[1] Univ Southampton, Geriatr Med Grp, Southampton SO9 5NH, Hants, England
[2] Univ Aberdeen, Hlth Serv Res Unit, Aberdeen AB9 1FX, Scotland
[3] Univ Southampton, MRC Epidemiol Res Ctr, Southampton SO9 5NH, Hants, England
[4] Univ Newcastle Upon Tyne, Ctr Hlth Serv Res, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England
[5] Univ Newcastle Upon Tyne, Sch Business, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England
[6] Freeman Rd Hosp, Musculoskeletal Unit, Newcastle Upon Tyne NE7 7DN, Tyne & Wear, England
[7] Hull York Med Sch, Off Dean, York, N Yorkshire, England
[8] Royal Infirm Edinburgh NHS Trust, Orthopaed & Trauma Unit, Edinburgh, Midlothian, Scotland
[9] Univ York, Dept Hlth Sci, York YO1 5DD, N Yorkshire, England
[10] Queens Med Ctr, Div Orthopaed & Accident Surg, Nottingham NG7 2UH, England