The role of stereoradiography in the evaluation of lower limb deformities

Abstract Deformities of the lower limbs are a common condition and can lead to changes in gait, as well as affecting the function and longevity of the hips, knees, and spine. A systematic approach is essential to achieve the desired therapeutic result with the lowest rate of complications. Panoramic radiography is a widely available, low-cost method that is commonly used in order to assess the length and angular deformities of the lower limbs, by measuring the length and angular deviations of the axes. However, because the combination of lower limb deformities in two or three orthogonal planes is common, conventional radiography lacks accuracy because it is a two-dimensional imaging method. Therefore, the measurements of valgus/varus deformities on X-rays restricted to the coronal plane will present increasing variations in measurements depending on the degree of flexion/recurvatum alignment, anomalous bone torsions, or, last but not least, inappropriate patient positioning. Low-dose biplanar stereoradiography using three-dimensional models increases the accuracy of the measurement of several parameters used in the evaluation of lower limb alignment, including lengths, axes, and tibial/femoral torsions, parameters that could previously be evaluated only by computed tomography. Stereoradiography also makes it possible to perform a head-to-toe evaluation, as well as to evaluate the interactions among the lower limbs, pelvis, and spine.

【摘要】下肢畸形是一种常见病症，可引发步态改变，同时影响髋关节、膝关节与脊柱的功能及使用寿命。要获得理想的治疗效果并将并发症发生率降至最低，需采用系统化的诊疗方案。全景放射摄影（panoramic radiography）是一种应用广泛且成本低廉的检查手段，临床常通过测量轴线长度与角度偏差，以此评估下肢的长度及成角畸形。然而，由于下肢同时存在两个或三个正交平面畸形的情况较为常见，而常规放射摄影属于二维成像技术，因此准确性欠佳。若仅在冠状面X线片上测量外翻/内翻畸形（valgus/varus deformities），其测量结果会随着屈曲/反曲对线异常、骨扭转异常，乃至患者体位不当等因素出现愈发显著的偏差。搭载三维模型的低剂量双平面立体X线摄影（low-dose biplanar stereoradiography）可提升多项下肢对线评估参数的测量精度，包括长度、轴线以及胫/股骨扭转度——这类参数此前仅能通过计算机断层扫描（computed tomography，CT）进行评估。此外，立体X线摄影还可实现从头到脚的全面评估，同时能够分析下肢、骨盆与脊柱之间的相互关联。