Double-bundle anterior cruciate ligament reconstruction: a comparative cadaver study of the femoral tunnels performed with in-out and out-in techniques

Introduction: Many authors have developed different techniques for reconstruction of both bundles (anteromedial AM; posterolateral PL) of the anterior cruciate ligament (ACL), in order to restore a normal kinematics. There are several factors that can influence biological integration of graft and the bundle’s mechanical behavior. The difference in diameter between tunnels on the intra-articular side and graft is one of most important. The aim of this study is to evaluate by CT-scan the femoral tunnel diameters performed using two different techniques. Methods: The study included 8 knees of 8 different cadavers divided into 2 groups. Group A: femoral tunnels were performed using an in-out technique: the PL tunnel from AM portal and the AM tunnel from transtibial PL tunnel. Group B: both tunnels were performed using an out-in technique with a guide developed by “senior author” (LP). A 7 mm reamer was used for all tunnels. The knees were then evaluated by CT-scan on coronal and axial planes. The diameters of the two tunnels were measured on both planes. Results: In group A, AM tunnel measured 7.07 mm (range 7 – 7.1) on axial plane and 7.02 mm (range 7 – 7.1) on coronal plane. In group B, AM tunnel measured 7.1 mm (range 7 – 7.2) on axial plane, and 7.15 mm (range 7 – 7.3) on coronal plane (p>0.05). In group A, PL tunnel measured 8.32 mm (range 8.2 – 8.4) on axial plane and 8.45 mm (range 8.4 – 8.5) on coronal plane. In group B, PL tunnel measured 7.15 mm (range 7 – 7.3) on axial plane and 7.02 mm (range 7 – 7.1) on coronal plane. (p<0.05). Discussion: There is not consensus on which is the best technique for double-bundle ACL reconstruction in terms of joint stability. Tunnel widening is one of the causes that may jeopardize the success of reconstruction and eventually a revision procedure. Several authors reported some difficulties in ACL revision surgery after single-bundle reconstruction when diameter of tunnel was larger than graft. Out-in technique shows a PL tunnel diameter similar to graft on intra-articular side. Theoretically, this approach can reduce the micro movements of the graft inside the tunnel due to the mismatch. Biomechanical and prospective randomized control studies between in-out and out-in techniques could confirm this hypothesis.