Optimal Anterolateral Ligament Tibial Tunnel Orientation to Prevent ACL Tunnel Collision and Saphenous Nerve Injury

Abstract

Background: Collision risks between femoral tunnels during combined anterior cruciate ligament (ACL) and anterolateral ligament (ALL) reconstruction have been reported. However, studies on collision risks between tibial tunnels and optimal ALL tibial tunnel orientation are lacking.

Purpose: To analyze the optimal orientation of the ALL tibial tunnel to minimize collisions with the ACL tibial tunnel while preventing injury to the saphenous nerve in combined reconstruction.

Study design: Descriptive laboratory study.

Methods: Preoperative magnetic resonance imaging (MRI) and postoperative computed tomography (CT) images of patients who underwent primary ACL reconstruction using the anteromedial portal technique were analyzed. Only patients with preoperative MRI scans including thin-cut images (<1 mm) were included for 3-dimensional (3D) reconstruction. Patients who underwent ALL reconstruction or had poorly 3D-reconstructed essential structures were excluded to ensure accurate reproduction of bony attachments and landmarks associated with ALL. Bony structures of the knee joint, including the proximal tibia with the actual ACL tibial tunnel, were reconstructed from the postoperative CT scans. The greater saphenous vein (GSV), which runs together with the saphenous nerve, was reconstructed from the preoperative MRI and subsequently transferred to the CT model, maintaining the appropriate positional relationship. Twelve orientations of the ALL tunnel (at 10° intervals, ranging from 0° to 20° anteriorly and from 0° to 30° distally) were simulated with the final 3D model, starting from the ALL tibial footprint (midpoint between the Gerdy tubercle and the fibular head, 10 mm distal to the joint line), to measure the distances between the ALL tunnel trajectory and other structures (ACL tibial tunnel, GSV) by each orientation.

Results: A total of 35 out of 304 patients were included in this study. An anteriorly oriented ALL tunnel decreased the minimum distance to the ACL tibial tunnel (MD-ACL) and increased minimum distance to the GSV (MD-GSV) (all P < .001). A distally oriented ALL tunnel increased MD-ACL and decreased MD-GSV (all P < .001). Optimal ALL tunnel orientation was 10° anterior to 30° distal (MD-ACL, 14.6 ± 4.0 mm; MD-GSV, 27.8 ± 12.4 mm) and 20° anterior to 30° distal (MD-ACL, 11.5 ± 3.6 mm; MD-GSV 43.6 ± 12.9 mm), considering both collisions with the ACL tunnel and the potential risk of injury to the saphenous nerve.

Conclusion: The optimal orientations of the ALL tibial tunnel to avoid collision with the ACL tibial tunnel and prevent saphenous nerve injury are 10° anterior to 30° distal and 20° anterior to 30° distal for far-cortex drilling techniques, starting from the midpoint between the Gerdy tubercle and the fibular head, 10 mm distal to the joint line.