Effects of knee flexion angles for graft fixation on force distribution in double-bundle anterior cruciate ligament grafts

Background: In double-bundle anterior cruciate ligament reconstruction, overloading either 1 of the 2 grafts should be avoided to decrease the risk of graft failure. Hypothesis: Overloading of the posterolateral graft may occur when it is fixed at 30 degrees of knee flexion because the posterolateral bundle is elongated as the knee approaches extension. Study Design: Controlled laboratory study. Methods: Ten human cadaveric knees were tested at (1) intact, (2) anterior cruciate ligament-deficient, (3) double-bundle anterior cruciate ligament reconstruction with the anteromedial and posterolateral grafts fixed at 60 degrees of flexion and full extension, respectively (fixation 60/FE), and (4) double-bundle anterior cruciate ligament reconstruction with both grafts fixed at 30 degrees of flexion simultaneously (fixation 30/30). Two external loading conditions simulating clinical examinations were used: (1) 134-N anterior tibial load and (2) combined rotatory loads of 10 N-m valgus and 5 N-m internal tibial torques. Data on knee kinematics and in situ forces in the 2 bundles of the intact anterior cruciate ligament and the respective grafts were obtained. Results: In response to 134-N anterior tibial load, knee kinematics and in situ force in the grafts were similar to the intact knee for both fixation protocols. The force in the anteromedial graft for fixation 60/FE was 34% higher, whereas the posterolateral graft for fixation 30/30 was 46% higher, compared with the intact anteromedial and posterolateral bundles, respectively. In response to combined rotatory loads, the posterolateral graft for fixation 30/30 carried 67% higher load than did the intact posterolateral bundle. Conclusion: Fixation 30/30 overloaded the posterolateral graft, whereas fixation 60/FE overloaded the anteromedial graft. Clinical Relevance: In double-bundle anterior cruciate ligament reconstruction, even though overall forces in the graft are the same as intact anterior cruciate ligament, the force distributions may not be the same as the intact bundles, and overloading of 1 of the 2 grafts may occur.