Optimal Knee Flexion Angle for ACL Femoral Tunnel Drilling and ALL Femoral Tunnel Orientation in Combined ACL and ALL Reconstruction: 3D Simulation Study

Background: In combined anterior cruciate ligament (ACL) and anterolateral ligament (ALL) reconstruction, there is a risk of collision between the femoral tunnels of the ACL and ALL. Purpose: To identify (1) the optimal knee flexion angle when creating the femoral tunnel for ACL reconstruction using the transportal technique and (2) the optimal orientation of the ALL femoral tunnel to minimize collisions between the tunnels. Study Design: Controlled laboratory study. Methods: Computed tomography scans from 10 participants were used to create 3-dimensional (3D) models. A 3D-reconstructed knee model at 90°of flexion was virtually further flexed to 5 different angles (100°-140°; 10° interval). Relationship between the ACL femoral tunnel created at 5 different flexion angles using transportal technique and ALL femoral tunnel created with 25 orientations (5 axial × 5 coronal) were analyzed. The minimal distance between tunnels was measured, and collisions between tunnels were investigated. The characteristics of each tunnel including tunnel length and wall breakage were also assessed. Results: An ACL femoral tunnel created at a knee flexion angle of 140° inevitably overlaps with ALL femoral tunnels in all orientations. Considering tunnel length and posterior wall blowout, knee flexion angles from 120° to 130° were considered suitable for ACL femoral tunnel drilling. The optimal ALL drill orientations to minimize collision between the tunnels were identified as axial 20° to coronal 0°, axial 30° to coronal 0°, and axial 30° to coronal 10°, demonstrating no collision between tunnels when the ACL femoral tunnel was created at a knee flexion of 120° to 130°. Conclusion: A knee flexion angle within the range of 120° to 130° in ACL femoral tunnel drilling and ALL drill orientations of axial 20° to coronal 0°, axial 30° to coronal 0°, and axial 30° to coronal 10° can be recommended as optimal conditions for creating tunnels while minimizing intertunnel collision in combined ACL and ALL reconstruction. Clinical relevance: This study provides practical guidelines for surgeons by identifying a safe range of knee flexion angles for ACL femoral tunnel creation using the transportal technique and optimal ALL femoral tunnel orientations. Applying these results may improve tunnel integrity, and enhance the success of combined ligament reconstructions.