[1] Univ Oxford, Nuffield Dept Orthopaed Rheumatol & Musculoskelet, Ctr Stat Med, Windmill Rd, Oxford OX3 7LD, England
[2] Univ Oxford, Nuffield Dept Orthopaed Rheumatol & Musculoskelet, Surg Intervent Trials Unit, Botnar Res Ctr, Windmill Rd, Oxford OX3 7LD, England
[3] Univ Aberdeen, Hlth Serv Res Unit, Hlth Sci Bldg, Aberdeen AB25 2ZD, Scotland