目的:利用骨盆数字重建图像(digital reconstructed radiographs，DRRs)研究如何选择正确的髋臼外上缘参考点测量儿童髋臼指数(AI)并初步探究其解剖对应关系。方法:回顾收集2015年1月1日至2015年12月31日入浙江大学医学院附属儿童医院骨科进行髋关节CT检查的研究对象共177例，收集满足条件患儿的髋关节CT数据，进行三维重建，包括多平面重建(MPR)、容积再现技术(VRT)。校正骨盆模型至标准位置后在CT后处理工作站中生成DRRs影像，分别采取髋臼外上部高密度弧线影终点A和其下方低密度骨性覆盖影最外上方点B作为参照点，测量其相应的髋臼指数(AAI和BAI)；选取通过股骨头最大直径的骨盆冠状位MPR图像，测量其CT髋臼指数(CTAI)，计算其差异。按旋转轴将骨盆模型进行前后倾斜，每增加或减少3°生成一张DRR图像，观察连续角度变化中A、B两点的位置改变，记录两点重合时的骨盆倾斜角度。利用配对n t检验验证CTAI、AAI、BAI之间差异的有效性；利用独立样本n t检验进行各组AAI和BAI差值的比较；利用Spearman相关分析和Bland-Altman分析检验两种测量结果之间的一致性。n 结果:纳入研究对象总共33例，年龄(2.90±1.32)岁；其中男8例，女25例，共52髋。CTAI与AAI的Spearman相关系数为0.92，其差值为(-0.41±1.83)°，差异无统计学意义，CTAI与AAI具有良好的一致性；CTAI与BAI的Spearman相关系数为0.81，两者差异具有统计学意义；AAI与BAI的差值为(3.06±3.06)°，该差值与骨盆X线片上髋臼显影形态有关。骨盆倾斜过程中，25髋在骨盆后倾时出现A、B点重叠，8髋在骨盆前倾时出现重叠，显示B点在不同髋关节中为髋臼前缘或者后缘的最外缘投影。结论:选择不同的髋臼外上缘点测量儿童髋臼指数将会导致巨大的差异，通过髋臼外上部高密度弧线影终点A测量的髋臼指数更加接近于真实的髋臼指数，能够更好的反映髋臼对股骨头的骨性覆盖。“,”Objective:To seek a correct mode of measuring acetabular index (AI) in children by using digital reconstructed radiographs (DRRs) and to identify the corresponding anatomy structures of these landmarks.Methods:A total of 177 subjects receiving hip computed tomograph (CT) examination from January 1, 2015 to December 31, 2015 were retrospectively collected. Hip CT data of children fulfilling the criteria were acquired for three-dimensional reconstruction, including multiplanar reconstruction (MPR) and volume rendering technique (VRT). After correcting the pelvic model to the standard position, DRR images were generated in CT post-processing workstation. The high-density arc shadow endpoint A in upper outer part of acetabulum and the outermost superior point B of low-density covering shadow below them were taken as the reference points respectively. Their corresponding acetabular indices of AAI and BAI were measured. Coronal MPR images of pelvis through the maximal diameter of femoral head were selected and their CT acetabular indices (CTAI) measured. The differences were calculated. According to the rotation axis, pelvic model was tilted anteroposteriorly a DRR image generated for every 3° increase or decrease. The position change of points A and B in continuous angle change were observed and pelvic tilt angle was recorded when two points coincided. Paired t-test was utilized for verifying the effectiveness of the differences between CTAI, AAI and BAI; independent sample t-test for comparing the differences between AAI and BAI in each group; Spearman's correlation and Bland-Altman analyses for testing the consistency between two measurements.Results:A total of 33 subjects aged (2.90±1.32) years were included. There were 8 males and 25 females with a total of 52 hips. The Spearman's correlation coefficient between CTAI and AAI was 0.92, and its difference was (-0.41±1.83)° and the difference was not statistically significant. CTAI agreed well with AAI; Spearman's correlation coefficient between CTAI and BAI was 0.81 and the difference was statistically significant; the difference between AAI and BAI was (3.06±3.06)° and this difference was related to acetabular development morphology on pelvic radiograph. During pelvic tilting, 25 hips showed an overlap of points A and B during pelvic retroversion and 8 hips revealed an overlap during pelvic anteversion. It indicated that point B was the outermost projection of anterior or posterior acetabular margin in different hips.Conclusions:A tremendous difference exists in selecting different landmarks during AI measurements. The measurement of AAI is closer to true AI and it may reflect femoral head coverage more accurately.