Biomechanics of double bundle anterior cruciate ligament reconstruction

The scope of this thesis was to verify whether anatomic reconstruction of the anterior cruciate ligament (ACL) with close replication of its two main bundles ensures better knee kinematics and improved clinical outcomes. The thesis articulates into three parts. In the first part the current anatomic knowledge is reviewed with regard to the double bundle ACL structure and an anatomic study is presented: its results will serve as a basis for the following kinematics and clinical studies. In the second part, a method to investigate cadaveric knee laxities is presented and employed to test intact and ACL deficient knees and to explore the function of the anteromedial and posterolateral ACL bundles. The ACL was found to be a primary restrain to anterior tibial translation mainly because of the action of the anteromedial bundle, with the posterolateral acting as a secondary restrain. Both bundles then were found to equally contribute to control the limit of internal rotation. Finally the reconstruction of both ACL bundles was demonstrated to be superior to traditional single bundle reconstruction in restoring intact knee anterior and rotational laxity. The third part focused on double bundle surgical technique with the development of surgical instruments that were validated on cadaver knees and found to be extremely accurate on the tibial side, less on the femur. Surgical technique was then improved and introduced into clinical practice. Two clinical studies were conducted and demonstrated the superiority of double bundle anatomic reconstruction in improving subjective and objective results as well as instrumented knee laxity measurements. In conclusion the main finding of this thesis was that, after a deep understanding of ACL anatomy and biomechanics, the replication at surgery of its native structure improves knee stability and patients’ satisfaction.