Force sharing between two grafts in the anatomical two-bundle anterior cruciate ligament reconstruction

The normal anterior cruciate ligament (ACL) can be generally divided into two main bundles, anteromedial bundle (AMB) and posterolateral bundle (PLB), and each bundle shared its function in response to external loads including anterior tibial drawer force. While we developed the anatomically oriented ACL reconstruction technique via two femoral tunnels and two parallel tibial tunnels (the "anatomical" two-bundle ACL reconstruction), there were few biomechanical studies about this technique. The purpose of this study was to investigate the force sharing between two separate grafts (anteromedial graft, AMG; posterolateral graft, PLG) in this anatomical two-bundle technique by measuring the force of each bundle in response to anterior tibial load. The anatomical two-bundle technique was performed on 11 patients via two tunnels at the superoposterior portion of the AMB footprint and the supero-posterior portion of the PLB footprint on the posterior margin of the lateral femoral condyle and two tunnels created in the center of the AMB and the PLB tibial footprints. After two doubled semitendinosus grafts were fixed with two EndoButton-CL(R)s on the femur, they were temporarily fixed to the tension-adjustable force gauge on the tibial cortex. After each bundle of the graft was settled at the tension of 25 N at 20 degrees, the force exerted on the two bundles was measured with the force gauge during applied anterior tibial force of 134 N at 0 degrees, 30 degrees, 60 degrees and 90 degrees of flexion. While the AMG carried 42.3 +/- 5.7% of and the PLG shared 57.7 +/- 5.7% of the total force at 0 degrees, the former took 64.1 +/- 11.1% and the latter was assigned 33.9 +/- 11.1% at 90 degrees. This study has demonstrated that the force distribution between the two grafts in the anatomical two-bundle technique was similar to that between the two bundles in the normal ACL.