everyone, and thank you for this opportunity to present. The study is a biomechanical analysis of ideal knee flexion angle for the ACL graft tensioning, utilizing six femoral and five tibial tunnel locations. Unfortunately, the authors have no relevant disclosures, and all the work was done in Pittsburgh. As a background, there's roughly 200,000 ACL reconstructions completed annually. However, most surgeons complete roughly 10 annually, demonstrating the importance of accurate tunnel placement. The ACL has been demonstrated to be an isometric, with length change throughout the sagittal range of motion. Tightened extension, lax in flexion, has a variable insertion pattern. A ribbon shape on the femur, a C shape on the tibia, demonstrating the difficulty of trying to recreate this with a circular tunnel. Graft failure rates have been demonstrated to be as high as 10%, with malpositioning being the main culprit, typically on the femoral side. Over-tightening can lead to re-rupture, and laxity can lead to instability. There are two common drilling techniques for tunnel placement. First is anatomic, where separate drill tunnels are done in the tibial and femoral and femur, and accuracy has been demonstrated to be roughly two millimeters and four millimeters, respectively, on the femur and tibia. The trans-tibial is one tunnel drilled through the tibia, through the femur. This has a more vertical graft orientation, and typically, accuracy is demonstrated to be within eight millimeters of the femoral footprint and six millimeters of the tibia-anatomic footprint. Excursion is throughout the sagittal plane of enroachment, and incorrect positioning can lead to clinical failure. So the objective of our study would be to see if there was a non-isometric, or excuse me, an isometric footprint, although we hypothesize that there's not, as that's been demonstrated previously, and then also determine the position of maximal excursion for the graft throughout the knee flexion. So we used 10 cadaveric knee specimens from femur to mid-tibia. Through an open approach, the ACL was transected. The center of the ACL remnant was identified in both the femur and the tibia, and correlated to the anatomic site as described by Dewan et al. Six femoral tunnels were drilled, and so if you can follow my mouse here, tunnel A was identified to be the anatomic insertion on the femur, and then five millimeter tunnels, which we just described a reasonable margin of error for all different directions were drilled, and same with the tibia as well. So six femur, five tibial, that's 30 combinations per knee specimen. They're drilled five millimeters apart. The knee was mounted with lateral side up, and a string potentiometer was used to measure graft excursion. So what we found, the ACL is not isometric, regardless of the femoral or tibial tunnel combination, and that tunnel location determines the flexion angle for maximum excursion of the graft. We found that the femoral tunnel was statistically significant, and that the tibial tunnel was not significant. This next slide's pretty busy, but if you bear with me, I'll explain it for you. On your x-axis is your femoral tunnels, so the six different tunnels. Your y-axis is your ACL excursion, so how much the graft moved throughout the course of motion, and the color coding is for your tibial tunnel. So as you can see, every single tunnel combination provided some sort of excursion of the ACL. Your maximum excursion changes with tunnel location, and again, we found the femoral tunnel was significant, no statistical significance with the tibial tunnel. So what can we learn from this? The flexion angle of maximum excursion changes depending on where your femoral tunnel is, and therefore you should adjust your, how you tighten your graft depending on where your tunnel is. So for example, if you do an anatomic drilling, so that would be an A on your femur, and an A on the tibia, that is tightest, or the most amount of excursion at zero degrees of flexion, and then it loosens when it's flexion, so therefore you decrease your risk of re-rupture. If you do trans-tibial, where you're more anterior, more proximal, that's tunnel E, and that should be tightened at 40 degrees of flexion. And then you can, this is, this graft here demonstrates the area of, or excuse me, the location where each graft is excruded the longest. So in conclusion, the femoral tunnel placement determines the degree at which the ACL is tightest, therefore you can adjust how you're going to, or how much flexion you're gonna secure your graft in, and then therefore you should tighten your angle, tighten your ACL graft at the angle of maximum excursion or tension, so that it doesn't stretch out throughout range of motion and increase your risk for re-rupture. Thank you.

biomechanical analysis

knee flexion angle

ACL graft tensioning

tunnel placement

ACL reconstruction