Centre for Therapeutic Innovation and Department of Mechanical Engineering, University of Bath, Bath, UK.
Department of Orthopaedics Leiden University Medical Center, Leiden, Netherlands.
Med Eng Phys. 2024 Aug;130:104201. doi: 10.1016/j.medengphy.2024.104201. Epub 2024 Jul 3.
Model-based Roentgen Stereophotogrammetric Analysis (RSA) is able to measure the migration of metallic prostheses with submillimeter accuracy through contour-detection and 3D surface model matching techniques. However, contour-detection is only possible if the prosthesis is clearly visible in the radiograph; consequently Model-based RSA cannot be directly used for polymeric materials due to their limited X-ray attenuation; this is especially clinically relevant for all-polyethylene implants. In this study the radiopacity of unicompartmental Ultra-High Molecular Weight Polyethylene (UHMWPE) knee bearings was increased by diffusing an oil-based contrast agent into the surface to create three different levels of surface radiopacity. Model-based RSA was performed on the bearings alone, the bearings alongside a metallic component held in position using a phantom, the bearings cemented into a Sawbone tibia, and the bearings at different distances from the femoral component. For each condition the precision and accuracy of zero motion of Model-based RSA were assessed. The radiopaque bearings could be located in the stereo-radiographs using Model-based RSA an accuracy comparable to metallic parts for translational movements (0.03 mm to 0.50 mm). For rotational movements, the accuracy was lower (0.1 to 3.0). The measurement accuracy was compared for all the radiopacity levels and no significant difference was found (p=0.08). This study demonstrates that contrast enhanced radiopaque polyethylene can be used for Model-based RSA studies and has equivalent translational measurement precision to metallic parts in the superior-inferior direction.
基于模型的 X 射线立体摄影分析（RSA）能够通过轮廓检测和 3D 表面模型匹配技术，以亚毫米的精度测量金属假体的迁移。然而，如果假体在射线照片中清晰可见，才能进行轮廓检测；因此，由于其有限的 X 射线衰减，基于模型的 RSA 不能直接用于聚合物材料；这在全聚乙烯植入物中尤其具有临床意义。在这项研究中，通过将油基对比剂扩散到表面来增加单室超高分子量聚乙烯（UHMWPE）膝关节轴承的射线不透明度，从而创造出三种不同水平的表面射线不透明度。对单独的轴承、用假体固定在位的轴承和金属部件、用假体固定在 Sawbone 胫骨上的轴承以及与股骨部件不同距离的轴承进行了基于模型的 RSA 分析。对于每种情况，都评估了基于模型的 RSA 中零运动的精度和准确性。使用基于模型的 RSA 可以在立体射线照片中定位射线不透明的轴承，其平移运动的准确性可与金属部件相媲美（0.03 毫米至 0.50 毫米）。对于旋转运动，准确性较低（0.1 至 3.0）。比较了所有射线不透明度水平的测量精度，未发现显著差异（p=0.08）。这项研究表明，增强射线不透明度的聚乙烯可用于基于模型的 RSA 研究，并且在上下方向上具有与金属部件相当的平移测量精度。
