Optimal tibial tunnel angulation for anatomical anterior cruciate ligament reconstruction using transtibial technique

Numerous studies have suggested that the primary cause of failure in transtibial anterior cruciate ligament reconstruction (ACLR) is often attributed to non-anatomical placement of the bone tunnels, typically resulting from improper tibial guidance. We aimed to establish the optimal tibial tunnel angle for anatomical ACLR by adapting the transtibial (TT) technique. Additionally, we aimed to assess graft bending angle (GBA) and length changes during in vivo dynamic flexion of the knee. Twenty knee joints underwent a CT scan and dual fluoroscopic imaging system (DFIS) to reproduce relative knee position during dynamic flexion. For the single-legged lunge, subjects began in a natural standing position and flexed the right knee beyond 90 degrees When performing the lunge task, the subject supported the body weight on the right leg, while the left leg was used to keep the balance. The tibial and femoral tunnels were established on each knee using a modified TT technique for single-bundle ACLR. The tibial tunnel angulation to the tibial axis and the sagittal plane were measured. Considering that ACL injuries tend to occur at low knee flexion angles, GBA and graft length were measured between 0 degrees and 90 degrees of flexion in this study. The tibial tunnel angulated the sagittal plane at 42.8 degrees +/- 3.4 degrees, and angulated the tibial axis at 45.3 degrees +/- 5.1 degrees The GBA was 0 degrees at 90 degrees flexion of the knee and increased substantially to 76.4 +/- 5.5 degrees at 0 degrees flexion. The GBA significantly increased with the knee extending from 90 degrees to 0 degrees (p < 0.001). The ACL length was 30.2mm +/- 3.0 mm at 0 degrees flexion and decreased to 27.5mm +/- 2.8 mm at 90 degrees flexion (p = 0.072). To achieve anatomic single-bundle ACLR, the optimal tibial tunnel should be angulated at approximately 43 degrees to the sagittal plane and approximately 45 degrees to the tibial axis using the modified TT technique. What's more, anatomical TT ACLR resulted in comparable GBA and a relatively constant ACL length from 0 degrees to 90 degrees of flexion. These findings provide theoretical support for the clinical application and the promotion of the current modified TT technique with the assistance of a robot to achieve anatomical ACLR.