The ACL consists of two functional bundles, anteromedial (AM) and posterolateral (PL), with differences in length change patterns during knee motion. Traditional single-bundle ACL reconstruction does not restore this complex anatomy. Biomechanical studies evaluate whether a more lateral 10 o’clock femoral tunnel better controls rotational loads compared to the typical 11 o’clock position.

A robotic testing system applied an anterior tibial load or combined internal rotation/valgus load to cadaveric knees that were intact, ACL-deficient, or reconstructed with a BPTB graft placed at 10 or 11 o’clock femoral tunnels in randomized order.1

With anterior tibial loading, anterior tibial translation was not different between tunnel positions except at 90° flexion where it was lower with the 11 o’clock tunnel. Under combined rotational loading, anterior translation was lower with the 10 versus 11 o’clock tunnel at 15° and 30° flexion, suggesting improved rotational control. In situ graft forces were also higher with the 10 o’clock tunnel at 30° flexion with rotational loading.

This cadaver study provides a biomechanical rationale for placing the femoral tunnel in a more lateral, 10 o’clock position to better reproduce PL bundle function and enhance rotational stability. However, neither position fully restored native ACL kinematics. Anatomic double-bundle ACL reconstruction may better replicate complex ACL function.

A randomized trial compared outcomes of single-bundle ACL reconstruction with femoral tunnels drilled using conventional 11 o’clock targeting versus a more lateral COMPAS (combined anatomic position) technique.2 At 2 year follow-up, patients in the COMPAS group had significantly lower pivot shift grades, greater improvement in quality of life scores, and faster return to sports compared to the conventional 11 o’clock position group. This provides clinical evidence supporting a lateralized femoral tunnel.

Limitations exist in extrapolating cadaveric biomechanical data to clinical outcomes. Surgeon experience and precision likely also influence the success of ACL reconstruction. Nevertheless, these studies give rationale for ongoing refinements in surgical technique.

Basic science studies suggest femoral tunnel placement in a more lateral, 10 o’clock position better controls rotational loads on the knee and replicates PL bundle function compared to the traditional 11 o’clock femoral tunnel position. Clinical data also support improved outcomes drilling the femoral tunnel using a lateralized approach. Anatomic ACL reconstruction techniques continue to evolve.

1. Loh JC, Fukuda Y, Tsuda E, et al. Knee stability and graft function following anterior cruciate ligament reconstruction: comparison between 11 o’clock and 10 o’clock femoral tunnel placement. 2002 Richard O’Connor Award Paper. Arthroscopy. 2003;19(3):297-304.

2. Desai N, Björnsson H, Musahl V, et al. Anatomic single- versus double-bundle ACL reconstruction: a meta-analysis. Knee Surg Sports Traumatol Arthrosc. 2014;22(5):1009-1023.