The X-Ray Magnification of the Hip for Preoperative Planning: A New Technique

Precise pre-op planning is fundamental for surgical precision in fit and fill of uncemented prostheses, and reliable and comparable radiographs are necessary for the early diagnosis of loosening. All this can be obtained with a given X-ray magnification factor. The Authors prove that the routinely used methods are misleading and suggest a new technique to obtain a uniform and/or measurable magnification in the A.P. radiograms of the hip. The method gives accurate measurements within a few tenths of a millimetre. It is based on the knowledge of the femoral position in relation to the X-ray film, obtained with a lateral radiographic view, and on mathematical calculation to obtain the X-ray focus height and position. Also in the case of a flexed and externally rotated hip, the non-uniform longitudinal and transverse magnifications can be measured.