An Anterior Cruciate Ligament In Vitro Rupture Model Based on Clinical Imaging

Background: Biomechanical studies on anterior cruciate ligament (ACL) injuries and reconstructions are based on ACL transection instead of realistic injury trauma. Purpose: To replicate an ACL injury in vitro and compare the laxity that occurs with that after an isolated ACL transection injury before and after ACL reconstruction. Study Design: Controlled laboratory study. Methods: Nine paired knees were ACL injured or ACL transected. For ACL injury, knees were mounted in a rig that imposed tibial anterior translation at 1000 mm/min to rupture the ACL at 22.5 degrees of flexion, 5 degrees of internal rotation, and 710 N of joint compressive force, replicating data published on clinical bone bruise locations. In contralateral knees, the ACL was transected arthroscopically at midsubstance. Both groups had ACL reconstruction with bone-patellar tendon-bone graft. Native, ACL-deficient, and reconstructed knee laxities were measured in a kinematics rig from 0 degrees to 100 degrees of flexion with optical tracking: anterior tibial translation (ATT), internal rotation (IR), anterolateral (ATT + IR), and pivot shift (IR + valgus). Results: The ACL ruptured at 26 +/- 5 mm of ATT and 1550 +/- 620 N of force (mean +/- SD) with an audible spring-back tibiofemoral impact with 5(o) of valgus. ACL injury and transection increased ATT (P < .001). ACL injury caused greater ATT than ACL transection by 1.4 mm (range, 0.4-2.2 mm; P = .033). IR increased significantly in ACL-injured knees between 0 degrees and 30 degrees of flexion and in ACL transection knees from 0 degrees to 20 degrees of flexion. ATT during the ATT + IR maneuver was increased by ACL injury between 0 degrees and 80 degrees and after ACL transection between 0 degrees and 60 degrees. Residual laxity persisted after ACL reconstruction from 0 degrees to 40 degrees after ACL injury and from 0 degrees to 20 degrees in the ACL transection knees. ACL deficiency increased ATT and IR in the pivot-shift test (P < .001). The ATT in the pivot-shift increased significantly at 0 degrees to 20 degrees after ACL transection and 0 degrees to 50 degrees after ACL injury, and this persisted across 0 degrees to 20 degrees and 0 degrees to 40 degrees after ACL reconstruction. Conclusion: This study developed an ACL injury model in vitro that replicated clinical ACL injury as evidenced by bone bruise patterns. ACL injury caused larger increases of laxity than ACL transection, likely because of damage to adjacent tissues; these differences often persisted after ACL reconstruction.