目的 研究Blumensaat线与胫骨平台之间的几何三角形关系是否可作为诊断和评估前交叉韧带（anterior cruciate ligament， ACL）损伤的辅助指标以提高诊断准确性。 方法 采用回顾性自身对照研究，招募2023年1—8月在青岛市市立医院经关节镜诊断并接受ACL重建的单侧ACL损伤患者64例，最终纳入40例；收集患膝的术前MRI图像以及健康膝关节的MRI图像，分别作为ACL损伤组和对照组。MRI图像中将Blumensaat线的最前端点、最后端点和中点分别定义为C点、D点和E点；将胫骨平台前缘和后缘的转折点分别定义为A点和B点；将DC延长线与AB线的交点定义为C'点；基于这些点，建立了∠DAB、∠CEB、∠DC'B和∠CDB。分析组内相关系数以评估测量的一致性和可重复性，比较上述角度之间的差异并计算受试者工作特征曲线下面积以评估诊断效能。 结果 对于∠CDB、∠DC'B、∠CEB 和∠DAB，组内和组间的相关系数值均超过0.80，表明具有良好的一致性和可重复性；与对照组相比，ACL损伤组的∠CDB、∠CEB 和∠DAB显著降低（P < 0.001）；∠DAB可能是诊断和评估ACL 损伤的最佳指标，其受试者工作特征曲线下面积为0.829，截断值为42.2°，敏感度为0.825，特异度为0.800。 结论 MRI图像中Blumensaat线与胫骨平台之间的几何三角形关系，尤其是∠DAB，可作为诊断和评估ACL损伤的一个辅助指标，有助于提高诊断的准确性。

Objective To investigate whether the geometric triangular relationship between the Blumensaat line and the tibial plateau can serve as an auxiliary diagnostic index for identifying and evaluating anterior cruciate ligament （ACL） injuries， thereby enhancing diagnostic accuracy. Methods A retrospective self?controlled study was conducted involving 64 patients diagnosed with unilateral ACL injury via arthroscopy and treated with ACL reconstruction at Qingdao Municipal Hospital from January to August 2023. Ultimately， 40 cases were included in the analysis. Preoperative MRI images of the affected knees and contralateral healthy knees were collected as the ACL injury group and control group， respectively. In the MRI images， point C， point D， and point E were defined as the anterior end， posterior end， and midpoint of the Blumensaat line， respectively； point A and point B were defined as the turning points of the anterior and posterior edges of the tibial plateau， respectively； and point C' was defined as the intersection of the extension line of DC and line AB. Based on these anatomical landmarks， angles ∠DAB， ∠CEB， ∠DC'B， and ∠CDB were established. The intra?class correlation coefficient （ICC） was calculated to assess measurement consistency and reproducibility. Differences between the aforementioned angles were compared， and the area under the receiver operating characteristic （ROC） curve was computed to evaluate diagnostic performance. Results For ∠CDB， ∠DC'B， ∠CEB， and ∠DAB， the intra?group and inter?group correlation coefficients all exceeded 0.80， indicating excellent consistency and reproducibility. Compared to the control group， the angles ∠CDB， ∠CEB， and ∠DAB in the ACL injury group were significantly reduced （P < 0.001）. Among these， ∠DAB appears to be the most reliable index for diagnosing and evaluating ACL injuries， with an area under the receiver operating characteristic curve （AUC） of 0.829， a cut?off value of 42.2°， a sensitivity of 82.5%， and a specificity of 80.0%. Conclusion The geometric triangular relationship between the Blumensaat line and the tibial plateau in MRI images， particularly the angle ∠DAB， can serve as an auxiliary indicator for diagnosing and evaluating ACL injuries， thereby enhancing diagnostic accuracy.