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

Introduction: Double bundle (DB) anterior cruciate ligament (ACL) reconstruction is nowadays a common procedure to manage ACL rupture. Many authors have reported in several short term follow-up prospective randomized studies a greater knee stability in DB reconstruction compared to single bundle. Despite several techniques reported in literature, as yet no study has demonstrated which DB technique has better outcomes. There are several factors that can influence biological integration of grafts and the bundle’s (anteromedial AM; posterolateral PL) mechanical behavior. The difference in diameter between tunnels on the intra-articular femoral side and graft is one of the most important. The aim of this study is to compare the diameter at the femoral tunnel entrance between two different techniques of DB ACL reconstruction in a cadaver model: the inside-out and the outside-in techniques. Hypothesis: The hypothesis is that a difference exists, in terms of diameter at the femoral tunnel entrance, between the abovementioned techniques. Materials and Methods: The study included 8 knees from 8 different cadavers divided into 2 groups. Group A: femoral tunnels were performed using an in-out technique: the PL tunnel from the AM portal and the AM tunnel from the transtibial PL tunnel. Group B: both tunnels were performed using an out-in technique with an out-in anatomical ACL guide system. All tunnels were drilled with a 7 mm acorn reamer. Upon cadaver dissection, the samples were evaluated by CT-scan on coronal and axial planes. The diameters of the two tunnels were measured on both planes. Results: Tunnel convergence was never observed in the two planes. 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). Conclusions: Double bundle ACL reconstruction is a promising technique in terms of clinical results and knee stability. However, there has been some criticism concerning the procedure. Indeed, tunnel enlargement and tunnel communication could jeopardize a revision ACL surgery. Our study showed that the PL femoral tunnel entrance diameter is significantly larger in the inside-out than outside-in technique. Theoretically, the out-in technique should determine an inferior PL tunnel enlargement after ACL reconstruction. Several other variables such as type of graft, fixation and rehabilitation program should also be considered. Biomechanical and prospective randomized control studies between in-out and out-in techniques could confirm this hypothesis.