Kinematic Impact of Anteromedial and Posterolateral Bundle Graft Fixation Angles on Double-Bundle Anterior Cruciate Ligament Reconstructions

Background: Currently in double-bundle anterior cruciate ligament (ACL) reconstructions, the range of knee flexion angles that surgeons use for anteromedial (AM) and posterolateral (PL) bundle graft fixation spans from 0 degrees to 90 degrees for both bundle grafts. Despite the recent popularity of this procedure, no consensus exists on an optimal set of AM and PL graft fixation angles. Hypothesis: Graft fixation angles that simulate the native tensioning relationship of the AM and PL bundles will produce kinematic results similar to the intact knee, while graft fixation angles that do not simulate this relationship will under- or overconstrain the knee. Study design: Controlled laboratory study. Methods: Twelve cadaveric knees were biomechanically tested in the intact state, ACL-sectioned state, and a randomized order of 7 double-bundle ACL reconstructed states at multiple graft fixation angle combinations. For each test state, data were collected for 88 N anterior tibial loads, 10 N.m valgus torques, 5 N.m internal rotation torques, and 2 simulated pivot shift loads consisting of a 5 N.m internal rotation torque coupled with either a 10 N.m valgus torque or an 88 N anterior tibial load at 0 degrees, 20 degrees, 30 degrees, 60 degrees, and 90 degrees of knee flexion. Results: The AM and PL graft fixation angle combinations of 0 degrees/0 degrees (AM graft fixation angle/PL graft fixation angle), 60 degrees/0 degrees, 45 degrees/15 degrees, and 75 degrees/15 degrees restored normal laxity to the reconstructed knee in all of the biomechanical tests. The 30 degrees/30 degrees, 60 degrees/60 degrees, and 90 degrees/90 degrees graft fixation angle combinations significantly restricted knee laxity compared with the intact state in various biomechanical tests. Conclusion: We found that as long as the PL bundle graft was fixed between 0 degrees and 15 degrees, the AM graft could be fixed up to 75 degrees without restricting knee laxity. However, fixation of the PL graft at 30 degrees of knee flexion and above significantly overconstrained the knee. Clinical Relevance: This study provides a range of angles that can be used in double-bundle ACL reconstructions to restore normal knee stability without causing overconstraint.