We have investigated the accuracy of the templating of digital radiographs in planning total hip replacement using two common object-based calibration methods with the ball placed laterally (method 1) or medially (method 2) and compared them with two non-object-based methods. The latter comprised the application of a fixed magnification of 121% (method 3) and calculation of magnification based on the object-film-distance (method 4). We studied the post-operative radiographs of 57 patients (19 men, 38 women, mean age 73 years (53 to 89)) using the measured diameter of the prosthetic femoral head and comparing it with the true value.Both object-based methods (1 and 2) produced large errors (mean/maximum: 2.55%/17.4% and 2.04%/6.46%, respectively). Method 3 applying a fixed magnification and method 4 (object-film-distance) produced smaller errors (mean/maximum 1.42%/5.22% and 1.57%/4.24%, respectively; p < 0.01). The latter results were clinically relevant and acceptable when planning was allowed to within one implant size. Object-based calibration (methods 1 and 2) has fundamental problems with the correct placement of the calibration ball. The accuracy of the fixed magnification (method 3) matched that of object-film-distance (method 4) and was the most reliable and efficient calibration method in digital templating.
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机译：我们已经研究了使用两种常见的基于对象的校准方法（将球放置在侧面（方法1）或内侧（方法2））将数字X线照片的模板在计划全髋关节置换中的准确性，并将其与两种基于非对象的方法进行了比较。后者包括应用121％的固定放大倍率（方法3）和基于物膜距离的放大倍数计算（方法4）。我们使用测量的股骨头假体直径并将其与真实值进行比较，研究了57例患者（19例男性，38例女性，平均年龄73岁（53至89岁））的术后X线照片。 1和2）产生较大的误差（平均值/最大值：分别为2.55％/ 17.4％和2.04％/ 6.46％）。采用固定放大率的方法3和方法4（物镜距离）产生的误差较小（平均值/最大值分别为1.42％/ 5.22％和1.57％/ 4.24％; p <0.01）。当允许在一个种植体大小范围内进行规划时，后一结果与临床相关，并且可以接受。基于对象的校准（方法1和2）具有正确放置校准球的基本问题。固定倍率的精度（方法3）与物膜距离（方法4）的精度匹配，是数字模板中最可靠，最有效的校准方法。
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