The aim of this study was to describe the three-dimensional orientation of the native anterior cruciate ligament (ACL) in magnetic resonance imaging (MRI) by calculating the angles of inclination in relation to the axial plane which is given for the knee joint line in a group of healthy individuals. These could help to establish guidelines that may be used for the surgical positioning of bone tunnels during ACL reconstruction. A total of 290 MRI scans of patients with integrity of the ACL were evaluated; three observers identified the coordinates of the femoral and tibial insertion sites, then it is defined the vector and evaluated its angles with respect to axial axis and calculated the angles with trigonometric equations. The data were analyzed according to the age, sex, side, BMI, and height of the patients, and the interobserver reliability was calculated. The patient demographics were as follows: age average: 45 years old, BMI average: 27.1, 54% right knees, and 60% female. The average angle for all the measurements was 76.95 degrees (SD ± 6.8 degrees) in the sagittal plane, 81.65 degrees (SD ± 7.79 degrees) in the coronal plane and 33.17 degrees (SD ± 4.98 degrees) in the axial plane. No statistically significant differences were found between the categorical variables mentioned; moderate to substantial interobserver reliability strength was found with an average kappa of 0.791 for all measurements. The three-dimensional orientation of the native ACL in a group of healthy individuals was established. The findings can be helpful for performing anatomical reconstructions of the ACL in injured patients using as reference the average calculated angles, or measure of the contralateral non-injured knee for surgical planning; these results serve as a basis for the design of a technique that optimizes the three-dimensional position of the ACL when it undergoes reconstruction in the trend toward greater precision for better functional results. Biomechanical and clinical-surgical studies are required to further evaluate our results.

本研究的目的是通过计算相对于膝关节线给出的轴向平面的倾斜角度，描述磁共振成像 (MRI) 中天然前十字韧带 (ACL) 的三维方向。一群健康的人。这些可能有助于建立可用于 ACL 重建期间骨隧道手术定位的指南。对总共 290 例 ACL 完整性患者的 MRI 扫描进行了评估；三位观察者确定股骨和胫骨插入部位的坐标，然后定义矢量并评估其相对于轴向轴线的角度，并用三角方程计算角度。根据患者的年龄、性别、体侧、BMI和身高对数据进行分析，并计算观察者间的信度。患者人口统计数据如下：平均年龄：45岁，平均BMI：27.1，54%为右膝，60%为女性。所有测量的平均角度在矢状面中为 76.95 度（SD ± 6.8 度），在冠状面中为 81.65 度（SD ± 7.79 度），在轴面中为 33.17 度（SD ± 4.98 度）。所提到的分类变量之间没有发现统计学上的显着差异；所有测量的观察者间可靠性强度为中等至显着，平均 kappa 为 0.791。建立了一组健康个体中原生 ACL 的三维定向。这些发现有助于对受伤患者进行 ACL 解剖重建，使用平均计算角度作为参考，或对侧未受伤膝关节进行测量以制定手术计划；这些结果可以作为一种技术设计的基础，该技术可以在重建时优化 ACL 的三维位置，以实现更高精度，以获得更好的功能结果。需要生物力学和临床外科研究来进一步评估我们的结果。