Risk of femoral tunnel collision in combined and independent anterolateral and anterior cruciate ligament reconstruction with outside-in femoral drilling

Objectives: In combined ACL and anterolateral ligament (ALL) reconstruction with outside-in femoral drilling, there is a risk of femoral tunnel collision. The objective was to determine the optimal combination of ACL and ALL femoral tunnel orientation to minimize the risk of collision. Methods: Forty patients with isolated ACLR with inside-out femoral drilling were included. For each patient, a postoperative MRI of the femur was reconstructed in 3D. An ALL tunnel was modeled virtually with a pair of coronal and axial angles varying from 0° to 40°. The minimum distance to the existing ACL tunnel was measured for each pair of angles. For each patient, based on the optimal ALL orientation identified, a correlation between the ACL angle in relation to the axial plane and the distance between the ACL and the ALL tunnel was established. Results: The lowest collision rate between the ACL and ALL tunnels was measured at 0% with a 0° coronal and 40° anterior axial ALL fixation angle. In order to avoid the risk of femoral trochlea breaking when the ALL femoral tunnel is being created, it should not exceed 30 mm in length. In this context, the risk of trochlea breaking by the guide pin was evaluated at 42%. The closer the orientation of the ACL tunnel to the axis of the femoral shaft, the greater the distance to the ALL tunnel, which decreases the risk of collision of the 2 tunnels. A fixation system without guide wire should be used if trochlear breaking of the ALL guide pin is to be avoided. Conclusion: In a combined inside-out ACL and ALL reconstruction, we recommend creating the ALL tunnel with a 0° coronal and 40° axial fixation angle and the ACL tunnel with the orientation closest to the axis of the femoral shaft.