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A simple guide to determine the magnification of radiographs and to improve the accuracy of preoperative templating

East Anglian Training Programme

M. T. Clarke, FRCS (Trauma & Orth), Orthopaedic Specialist Registrar

Orthopaedic Research Unit, Cambridge University, Hills Road, Cambridge CB2 2QQ, UK.

J. P. Hallett, FRCS, Consultant Orthopaedic Surgeon

Ipswich Hospital NHS Trust, Heath Road, Ipswich IP4 5PD, UK.

Correspondence should be sent to Mr K. S. Conn at the Department of Orthopaedic Surgery, North Hampshire Hospitals NHS Trust, Aldermaston Road, Basingstoke, Hampshire RG24 9NA, UK.

Templates are used in the preoperative planning of many orthopaedic procedures. The magnification of the bones on preoperative radiographs can vary despite using standardised radiological techniques. Templates will give misleading measurements unless this magnification is quantified.

A coin may be used to calculate the magnification, with significant improvement in the accuracy of templating (p = 0.05). A group of patients undergoing uncemented arthroplasty of the hip was at high risk for intraoperative fracture of the femur because the magnification of the radiograph was larger than that of the template.

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