Objective: To propose a method to determine the unreasonableness of the fixed angle in posterior atlantoaxial fusion surgery based on the ratio of line segments between anatomical landmarks of the atlantoaxial joint. Methods: A cross-sectional study was conducted. According to the inclusion criteria, a screening was performed on the database of asymptomatic volunteers who had full-spine lateral X-ray films taken at the Second Affiliated Hospital of Wenzhou Medical University from May 2016 to May 2021. A total of 207 volunteers were included, comprising 98 males with an age of (40.68±13.87) years and 109 females with an age of (42.64±14.45) years. On the lateral X-ray film, a line (L) parallel to the posterior margin of the odontoid process was drawn at the posterior edge of the lower articular surface of the axis (a), intersecting the atlas at points b, c, and d. The line segments ab, bd, bc, and the C1-C2 angle were measured, and the ratios of bd/ab and bc/ab were calculated. The ability of bd/ab and bc/ab to predict the unreasonable fixed angle of the atlantoaxial joint (≥22°) was analyzed by receiver operating characteristic (ROC) curve analysis in both male and female. The areas under the ROC curves (AUC) were calculated, and the performance of the two prediction methods was compared using the Delong's test. The cutoff value for distinguishing the unreasonableness of the C1-C2 angle and the sensitivity and specificity were calculated. Results: The ROC curve analysis in the male group showed that the AUC of bc/ab for predicting the unreasonable C1-C2 angle was 0.791 (95%CI: 0.696-0.867, P<0.001), with a cutoff value of 0.449, sensitivity of 97.3%, and specificity of 70.0%. The performance was significantly better than that of bd/ab (cutoff value 1.100, AUC=0.532, 95%CI: 0.428-0.634, sensitivity 26.3%, specificity 83.3%, P<0.001). The ROC curve analysis in the female group showed that the AUC of bc/ab for predicting the unreasonable C1-C2 angle was 0.804 (95%CI: 0.745-0.852, P<0.001), with a cutoff value of 0.488, sensitivity of 90.5%, and specificity of 58.6%. The performance was significantly better than that of bd/ab (cutoff value 0.960, AUC=0.687, 95%CI: 0.624-0.748, sensitivity 90.5%, specificity 44.8%, P=0.041). Conclusions: The bc/ab value can be used as an effective indicator to predict the unreasonable C1-C2 angle in posterior atlantoaxial fusion surgery with high diagnostic accuracy. The cutoff value for males is<0.449, and for females is<0.488.
目的： 研究一种基于寰枢椎解剖标记点间线段比值判断寰枢椎后路固定融合术中固定角度是否合理的方法。 方法： 横断面研究。根据纳入标准从2016年5月至2021年5月在温州医科大学附属第二医院拍摄有脊柱全长侧位X线片的无症状志愿者库中进行筛选，共纳入207例志愿者数据，其中男98例，年龄（40.68±13.87）岁，女109例，年龄（42.64±14.45）岁。在侧位X线片上过枢椎下关节面后缘（a）作平行于齿状突后缘的直线（L），分别交寰枢椎于点b、c和d，测量线段ab、bd、bc、C1-C2角并计算bd/ab和bc/ab值。分别在男性组和女性组中对bd/ab和bc/ab两个数值预测寰枢椎固定角度不合理（≥22°）的能力进行受试者工作特征（ROC）曲线分析，计算两种ROC曲线下面积（AUC），并用Delong检验比较两种预测方式的性能，确定区分C1-C2角度是否合理的截断值并计算其灵敏度和特异度。 结果： 男性组ROC曲线分析结果显示，bc/ab值预测C1-C2角不合理的AUC为0.791（95%CI：0.696~0.867，P<0.001），截断值为0.449，灵敏度为97.3%，特异度为70.0%，检验性能显著优于bd/ab值（截断值1.100，AUC=0.532，95%CI：0.428~0.634，灵敏度为26.3%，特异度为83.3%，P<0.001）。女性组ROC曲线分析结果显示，bc/ab值预测C1-C2角不合理的AUC为0.804（95%CI：0.745~0.852，P<0.001），截断值为0.488，灵敏度为90.5%，特异度为58.6%，检验性能显著优于bd/ab值（截断值为0.960，AUC=0.687，95%CI：0.624~0.748，灵敏度为90.5%，特异度为44.8%，P=0.041）。 结论： bc/ab值可作为寰枢椎后路固定融合术中用于预测C1-C2角度不合理的有效指标，并具有较高的诊断精度，其在男性中的截断值为<0.449，在女性中的截断值为<0.488。.