A device to measure X-ray magnification in preoperative planning for cementless arthroplasty

Non-cemented press fit prostheses require a high degree of surgical precision for success. Since components vary in size by millimeters, the optimum preoperatively-determined size becomes a vital factor in selecting the correct size at the time of surgery. The preoperatively-determined component size is useful only if the information is obtained in a reliable and reproducible manner. The proper sequence combines X-rays of known magnification and templates of corresponding magnification. X-ray magnification is not a constant value even if the X-ray tube is maintained at a standardized height. Variables such as patient size and positioning make magnification measurements a necessity for every X-ray taken. A dense lead plate was designed for this purpose because commercially-available devices are over-penetrated by the X-ray exposures routinely used for hip roentgenograms. Manufacturers can provide templates in varying magnifications. This makes it possible to obtain a high correlation between the preoperative choice and the actual size chosen at surgery.