Department of Orthopedic Surgery, Stavanger University Hospital, Stavanger, Norway.
Department of Public Health, The Faculty of Health Sciences, University of Stavanger, Stavanger, Norway.
PLoS One. 2024 Aug 22;19(8):e0307259. doi: 10.1371/journal.pone.0307259. eCollection 2024.
Calibrated pelvic X-ray images are needed in the preoperative planning of total hip arthroplasty (THA) to predict component sizes. Errors and mismatch in the size of one or more components are reported, which can lead to clinically relevant complications. Our aim is to investigate whether we can solve the fundamental problem of X-ray calibration and whether traditional X-ray still has a place in preoperative planning despite improved radiological alternatives.
Based on geometric and radiographic principles, we estimate that the magnification factor is adapted to the X-ray device and depends strongly on the source-image distance of the device. We analyse the errors of the various calibration methods and investigate which narrow range can be expected to show that the center of rotation is sufficiently accurate. Based on the results of several CT-scans we defined an adapted magnification factor and validated the degree of measurement accuracy.
The true magnification of objects on X-ray images depends mainly on the device settings. Stem size prediction is possible to a limited extent, with an error margin of 4.3%. Components can be predicted with a safety margin of one size up and down as with CT or 3D images. The prerequisite is that the source-image distance is greater than or equal to 120 cm, the table-image distance is known, and the object-image distance is estimated according to the patient's BMI. We defined a device-adapted magnification factor that simplifies the templating routine and can be used to obtain the most reliable preoperative dimensional measurements that can be expected from X-ray images. We found the error margin of the magnification factor with the highest degrees of prediction and precision.
Preoperative planning is reliable and reproducible using X-ray images if calibration is performed with the device-adapted magnification factor suggested in this paper.
全髋关节置换术（THA）术前规划需要校准骨盆 X 射线图像，以预测假体尺寸。报告了一个或多个组件的尺寸存在误差和不匹配的情况，这可能导致临床相关并发症。我们的目的是研究是否可以解决 X 射线校准的基本问题，以及尽管有改进的影像学替代方案，传统 X 射线在术前规划中是否仍有一席之地。
基于几何和放射学原理，我们估计放大系数适应 X 射线设备，并且强烈依赖于设备的源像距。我们分析了各种校准方法的误差，并研究了可以预期的狭窄范围，以表明旋转中心足够准确。基于几例 CT 扫描的结果，我们定义了一个适应的放大系数，并验证了测量精度的程度。
X 射线图像上物体的真实放大率主要取决于设备设置。可以在一定程度上预测柄的尺寸，误差范围为 4.3%。可以预测假体的尺寸，安全范围为一个尺码的上下，与 CT 或 3D 图像相同。前提是源像距大于或等于 120 厘米，知道台面图像距离，并且根据患者的 BMI 估计物像距离。我们定义了一个设备适应的放大系数，简化了模板制作常规，可以获得最可靠的术前尺寸测量，这是 X 射线图像可以预期的。我们发现了预测和精度最高的放大系数的误差范围。
如果使用本文中建议的设备自适应放大系数进行校准，使用 X 射线图像进行术前规划是可靠且可重复的。
