Oblique Femoral Tunnel Placement Can Increase Risks of Short Femoral Tunnel and Cross-Pin Protrusion in Anterior Cruciate Ligament Reconstruction

Background: A more horizontal femoral tunnel has been emphasized for contemporary anterior cruciate ligament (ACL) reconstruction. However, lowering the femoral tunnel may result in a shorter tunnel. In addition, a more horizontally placed femoral tunnel may have inadequate bone stock at the posterior portion of the tunnel, which can lead to protrusion of the cross-pin (Rigidfix) system for femoral fixation. Hypothesis: A more horizontal femoral tunnel position, particularly via the anteromedial (AM) portal technique, will reduce femoral tunnel length, and a more horizontal femoral tunnel position and anterior-to-posterior pin insertion will increase the risk of Rigidfix pin protrusion. Study Design: Controlled laboratory study. Methods: In 10 cadaveric knees, we measured maximum lengths of the femoral tunnels at the positions of 11:30, 10:30, and 9:30 o'clock using the transtibial technique and at the 10:30 and 9:30 o'clock using the AM portal technique. Then, for each femoral tunnel via the transtibial technique at 11:30, 10:30, and 9:30 o'clock positions, tests were performed for 3 directions of Rigidfix pin insertion using the lateral epicondyle as an anatomical landmark, namely, 150 anterior to posterior (A-P), neutral, and 150 posterior to anterior (P-A). It was then determined whether pins protruded from the posterior cortex. Results: The lengths of femoral tunnels produced using the transtibial technique became shorter as the femoral starting position became more horizontal (51.1 mm, 40.0 mm, and 34.2 mm on average at the 11:30, 10:30, and 9:30 o'clock position, respectively). Tunnels made using the AM portal technique were significantly shorter than those made using the transtibial technique: by 7.6 mm at the 10:30 o'clock and 4.5 mm at the 9:30 o'clock positions on average (P < .001). In addition, increasing obliquity increased the likelihood of Rigidfix pin protrusion, especially when pins were inserted in the A-P direction. Conclusion: The current effort to lower the femoral tunnel position in ACL reconstruction can shorten the tunnel length and compromise the graft fixation at the femur using the Rigidfix system. Clinical Relevance: When an intended femoral tunnel position is more horizontal than the 10:30 o'clock position for ACL reconstruction, a surgeon needs to be cautious regarding a short femoral tunnel, particularly when using the AM portal technique, and possible protrusion of the cross-pin (Rigidfix) fixator.