Investigating the Role of the Femoral Tunnel Position on Knee Biomechanics in ACL Reconstruction

Abstract

The femoral tunnel position for the graft plays a critical role in the success of anterior cruciate ligament (ACL) reconstruction surgery. Malposition of the femoral tunnel is one of the top reasons for graft failure in this procedure. Despite the potential benefits of surgical navigation systems for ACL reconstruction to aid in more accurate femoral tunnel positioning, there has been no significant adoption or evidence of improved clinical outcomes with navigated ACL reconstruction procedures. However, this may stem from a lack of understanding of how the femoral tunnel position in ACL reconstruction alters the biomechanics of the knee joint relative to the native knee. To address this knowledge gap, the goals of this work were to (1) investigate the role of the femoral tunnel position in its influence on knee biomechanics, and (2) design and develop a proof-of-concept surgical navigation system to aid in selection and placement of the femoral tunnel. For the first goal, an in vitro study investigated the influence of five different femoral tunnel positions on knee kinematics, force carried by the graft, and on graft length change over flexion. Varying femoral tunnel insertion led to statistically significant kinematic differences in anterior tibial translation range at 90 degrees of knee flexion. As well, different femoral tunnel positions led to significant differences in the force carried by the graft compared to the estimated force carried by the intact ACL at all knee flexion angles. Graft length change over knee range of motion showed that an anteriorly placed femoral tunnel is more isometric while a posteriorly placed graft had the greatest change in length. For the second goal of this work, a surgical navigation system workflow was developed based on these insights to allow for the calculation of graft length changes intraoperatively over different knee flexion angles. A proof-of-concept system with this feature was developed in 3D Slicer using the SlicerIGT extension. This work enhances understanding of how the femoral tunnel position affects knee biomechanics and how surgical navigation systems can be designed to provide surgeons with methods to better identify and position the femoral tunnel for ACL reconstruction surgery.