1. Robert Jones and Agnes Hunt Orthopaedic Hospital, Hospital NHS Trust, Oswestry, Shropshire SY10 7AG, UK.
2. University Hospital of Wales, Heath Park, Cardiff, Wales CF14 4XW, UK.
3. Royal Shrewsbury Hospital, Mytton Oak Road, Shrewsbury, Shropshire SY3 8XQ, UK.
4. University of North Staffordshire Trust, The Royal Infirmary, Princes Road, Stoke-on-Trent, Staffordshire ST4 7LN, UK.