Rationale for Strategic Graft Placement in Anterior Cruciate Ligament Reconstruction: I.D.E.A.L. Femoral Tunnel Position.

In the United States, surgeons perform an estimated 200,000 anterior cruciate ligament reconstructions (ACLRs) each year. Over the past decade, there has been a surge in interest in defining anterior cruciate ligament (ACL) anatomy to guide ACLR. With this renewed interest in the anatomical features of the ACL, particularly the insertion site, many authors have advocated an approach for complete or near-complete “footprint restoration” for anatomical ACLR. Some have recommended a double-bundle (DB) technique that completely “fills” the footprint, but it is seldom used. Others have proposed centralizing the femoral tunnel position within the ACL footprint in the hope of capturing the function of both the anteromedial (AM) and posterolateral (PL) bundles. Indeed, a primary surgical goal of most anatomical ACLR techniques is creation of a femoral tunnel based off the anatomical centrum (center point) of the ACL femoral footprint. With a single-bundle technique, the femoral socket is localized in the center of the entire footprint; with a DB technique, sockets are created in the centrums of both the AM and PL bundles. Because of the complex shape of the native ACL, however, the strategy of restoring the femoral footprint with use of either a central tunnel or a DB approach has been challenged. The femoral footprint is 3.5 times larger than the midsubstance of the ACL. Detailed anatomical dissections have recently demonstrated that the femoral origin of the ACL has a stout anterior band of fibers with a fanlike extension posteriorly. As the ACL fibers extend off the bony footprint, they form a flat, ribbonlike structure 9 to 16 mm wide and only 2 to 4 mm thick. Within this structure, there is no clear separation of the AM and PL bundles. The presence of this structure makes sense given the anatomical constraints inherent in the notch. Indeed, the space for the native ACL is narrow, as the posterior cruciate ligament (PCL) occupies that largest portion of the notch with the knee in full extension, leaving only a thin, 5-mm slot through which the ACL must pass. Therefore, filling the femoral footprint with a tubular ACL graft probably does not reproduce the dynamic 3-dimensional morphology of the ACL. In light of the discrepancy between the sizes of the femoral footprint and the midsubstance of the native ACL, it seems reasonable that optimizing the position of the ACL femoral tunnel may be more complex than simply centralizing the tunnel within the footprint or attempting to maximize footprint coverage. In this article, we amalgamate the lessons of 4 decades of ACL research into 5 points for strategic femoral tunnel positioning, based on anatomical, histologic, isometric, biomechanical, and clinical data. These points are summarized by the acronym I.D.E.A.L., which refers to placing a femoral tunnel in a position that reproduces the Isometry of the native ACL, that covers the fibers of the Direct insertion histologically, that is Eccentrically located in the anterior (high) and proximal (deep) region of the footprint, that is Anatomical (within the footprint), and that replicates the Low tension-flexion pattern of the native ACL throughout the range of flexion and extension.