How to drill the talar tunnel in ATFL reconstruction?

Purpose: Reconstruction of the anterior talofibular ligament may be indicated in cases of residual instability after conservative treatment. Often, a bone tunnel is used for fixation in the talar bone. The purpose of this study is to evaluate possible routes for drilling the talar tunnel. Methods: Virtual tunnels were generated in a 3D bone model, oriented towards the following external landmarks: the talar neck, the most anterior point of the medial malleolus (MM), the most distal point of the MM, the most medial point of the MM, and the most posterior point of the MM. The parameters analysed for tunnels with lengths of 20, 25, and 30 mm were the maximum distance inside the bone and the distance from the tunnel to the bone surface. A minimal safe distance (MSD) was calculated for a tunnel with a diameter of 5 mm. Results: The shortest measured distance before arriving outside the talar bone was 16.7 mm. The longest distances were obtained in the tunnels oriented towards the talar neck (mean value of 36.6, SD 2.8) and towards the most posterior point of the MM (mean value of 35.8, SD 0.3). Only one tunnel, measuring 20 mm in depth and oriented towards the most posterior point of the MM, revealed no individual values below the MSD. Conclusion: External landmarks are useful for drilling a talar tunnel during reconstruction of the anterior talofibular ligament. Only one tunnel, oriented towards the most posterior point of the MM, measuring 5 mm in diameter and with a maximum depth of 20 mm, was safe in all individuals. Surgeons should be aware of these limits when treating patients with ankle instability.