Department of Orthopedic Surgery and Traumatology, University Hospital Freiburg, Freiburg, Germany; Eye Center, Medical Center, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
Department of Orthopedic Surgery and Traumatology, University Hospital Freiburg, Freiburg, Germany.
J Arthroplasty. 2018 Aug;33(8):2652-2659.e3. doi: 10.1016/j.arth.2018.02.023. Epub 2018 Mar 2.
Correct positioning of the cup is an important factor in total hip arthroplasty. Assessing its position from a plain anteroposterior pelvic radiograph is known to be hampered by systemic errors. This study focuses on developing a correction method to adjust for these potential sources of error and to eliminate them based on a 3D geometric analysis.
Computed tomography scans of 113 (66 male, 47 female) pelvices were reconstructed and virtually projected onto a plain radiograph with varying rotational and translational positions. Thus cup inclination and anteversion as measured on a 2D-radiograph and in the 3D environment were correlated. Projected offset of the symphysis from the mid-sacrum served as a mean to measure pelvic right/left-rotation. Pelvic tilt was determined from the projected height of the contour of the small pelvis. Correction formulas were verified by projecting a gimbal-mounted artificial pelvis with a cup implanted in a known position.
We found gender-specific formulas that correct for malrotated and off-centered radiographs. Applying these formulas cup inclination was assessed as close as 1.3° (±1.90°) to the true 3D value and cup anteversion as close as 1° (±1.91°) although deviations between directly measured plain values and corrected values rose up to 18°.
Inherent effects of central projection and malrotations due to pelvic tilt, pelvic rotation, and noncentered radiographs are corrected. Evaluation of radiographic inclination and anteversion of acetabular cups from plain 2D-radiographs show improved precision. Real values are approached better than 1.3° when applying our correction formulas.
髋臼杯的正确位置是全髋关节置换术的一个重要因素。从骨盆前后位平片评估其位置已知会受到系统误差的影响。本研究专注于开发一种校正方法，以调整这些潜在的误差源，并基于 3D 几何分析消除这些误差。
对 113 个（66 名男性，47 名女性）骨盆的计算机断层扫描进行重建，并以不同的旋转和平移位置虚拟投影到普通射线照片上。因此，在二维射线照片和三维环境中测量的髋臼杯倾斜度和前倾角相关联。耻骨联合相对于中骶骨的投影偏移被用作测量骨盆左右旋转的平均值。骨盆倾斜度由骨盆轮廓的投影高度确定。通过将安装在已知位置的髋臼杯的万向节式人工骨盆投影来验证校正公式。
我们发现了针对旋转不正和偏心射线照片的性别特异性公式。应用这些公式，髋臼杯倾斜度的评估结果与真实 3D 值的偏差接近 1.3°（±1.90°），髋臼杯前倾角的评估结果与真实 3D 值的偏差接近 1°（±1.91°），尽管直接测量的平片值和校正值之间的偏差高达 18°。
本研究校正了中心投影和由于骨盆倾斜、骨盆旋转和非中心射线照片引起的旋转不正的固有影响。从普通二维射线照片评估髋臼杯的射线照相倾斜度和前倾角显示出更高的精度。应用我们的校正公式，接近真实值的精度优于 1.3°。
