For this talk, I'm going to be speaking about ACL grafts, tunnels, and fixation, how to avoid common mistakes. These are my disclosures, none of which are directly relevant to this talk. As an overview, I'm going to touch very briefly on the anatomy of the ACL, and then really go into detail on graft choices, tunnel placement, and graft fixation, and how we can avoid some mistakes. As we're all aware, the ACL is comprised of two bundles. The anteromedial bundle resists anterior tibial translation, while the posterolateral bundle provides rotational stability. In full extension, the bundles are parallel, whereas at 90 degrees of flexion, the posterolateral bundle moves anterior. The ACL is supplied by the middle geniculate artery. Now, in terms of graft choice, we have a lot of options. The two broad categories are autograft and allograft, and there are several options within each. I'm going to touch on the pros and cons of each of those. Overall, the ideal ACL graft will reproduce the native anatomy and biomechanics of the normal ACL. We want it to have strong initial fixation, rapid biologic incorporation, and a low rate of donor site morbidity. Additionally, we want to have low or no rate of disease transmission. We want the patient to have optimal clinical outcomes, and of course, we want the graft to be cost-effective, and we often need to take that into account. The native ACL, these are the biomechanics of the native ACL. Now, here we see the biomechanics of all of our graft options, and as you can see, they are all stronger than the native ACL. Here's a table summarizing the different graft options. It's a little bit busy, but I'm going to go into detail on these things. The bottom line is there's really no gold standard, and each graft has its own characteristics. Allograft, there are certainly some advantages. There's no harvest morbidity. It's faster surgical time, slightly less loss of knee range of motion. There are a lot of different tissue sources available. It's less painful for the patient and leads to an easier recovery, and in theory, there's limitless tissue. The disadvantage is that there's delayed graft incorporation, and there can be disease transmission, although that risk is very low. Additionally, there's decreased mechanical property due to sterilization methods, and that's why ideally the graft would be non-irradiated. There's increased cost, of course, and higher failure rates have definitely been demonstrated in young, active patients. The quadruple hamstring graft is a very common autograft. The advantages include less harvest morbidity, less anterior knee and kneeling pain. It's a nicer incision. In fact, that's the same incision you're going to make for your tibial tunnel. There's less quad weakness because you don't invade the extensor mechanism, and it's the strongest initial graft construct. Some disadvantages are that there can be premature truncation of the graft, and that is a huge, huge problem. You can also injure the MCL, which is directly below the hamstring autograft. There's bone-to-soft tissue healing. You can lose flexion, there's hamstring weakness, and some studies demonstrate a higher revision rate. I included this slide just to demonstrate the hamstring tendons you're going to harvest To emphasize the point that it is absolutely critical that you free up and release all adhesions, all fascial bands attached to the tendons, because otherwise, you will end up truncating the graft prematurely, and you'll be left with a very short hamstring autograft. At that point, you'll either have to turn to another autograft option or use allograft. Another problem that we can encounter with hamstring autografts, which deters some surgeons from using this frequently, is that there's often a very thin diameter of the hamstrings. In that case, we want it to be at least eight millimeters. If it's not at least eight millimeters, you should consider augmenting with allograft. Btb graft, the advantages include less clinical failures. It tends to be the graft of choice in high-demand athletes. There's earlier graft incorporation because of the bone-to-bone healing, less hamstring weakness, and in many cases, a faster recovery. The disadvantages include more graft harvest morbidity. It's a big incision on the front of the knee, and that leads to anterior knee and kneeling pain. Patients can have more quad weakness and atrophy, and you can injure the infrapatellar branch of the saphenous nerve. Quad autograft is a graft that definitely has been gaining popularity over the past several years. The advantages of this graft include that you can use it with or without a bone block. It's a very strong graft. It's reliable. It's always a robust graft. It's large diameter. You certainly can use it in revision situations, and there's minimal donor site morbidity. There's really no anterior knee pain or anterior numbness because of where you're harvesting from. The disadvantages include increased risk of proximal patellar fracture if you're harvesting a bone plug, lack of bone-to-bone healing if you only use the soft tissue component, and there's a risk of rectus femoris retraction or injury. Patients can also have loss of extension and quad weakness similar to BTB graft. Now, in terms of ACL graft selection, there are a lot of factors that influence this. Absolutely, surgeon experience, preference, and comfort are important and influence graft selection, patient age, and activity level. We also need to take into account patient sport or occupation, their desire to return to work or return to play, and their comorbidities. We also want to understand prior surgery and have a very detailed discussion with the patient to understand their preference and their expectations. Additionally, we factor in rehab concerns. This is kind of summarizing the ACL grafts and some factors you may take into account. For BTB autograft, maybe consider that in high-demand young athletes and certainly could be used for a revision of a failed soft tissue graft. Cold hamstring autograft, maybe recreational athletes younger than the age of 40, high-demand young athletes with patellar tendon problems, you may consider this graft as well. Quad tendon autograft really is a phenomenal graft. For me personally, this is now my go-to graft for primary ACL reconstruction because it is just so reliable and a very robust graft and a pretty straightforward harvest. Allograft tendons, really we tend to reserve those for older recreational athletes. These are all just things to take into account. Just one study kind of highlighting quad tendon versus hamstrings and BTB. The purpose of this was to evaluate outcomes of quad tendon autografts and to review clinical studies comparing quad tendon versus BTB and hamstring autografts in terms of several outcomes. They had 27 clinical studies with about 2,900 patients. In terms of quad tendon versus BTB, there was no significant difference in several outcomes, but patients with quad tendon graft had less donor site pain. When comparing quad tendon and hamstring autografts, there was no significant difference in several parameters, but those with quad tendon autografts had improved mean Leisholm scores. The authors therefore concluded that quad tendon autograft had comparable clinical and functional outcomes and graft survival rate compared with BTB and hamstring tendon autografts. Quad tendon autografts showed significantly less harvest site pain compared to BTB and better functional outcome scores compared with hamstring tendon autograft. In terms of tunnel placement, the femoral tunnel can be placed either trans-tibial or via independent femoral tunnel drilling. With trans-tibial drilling, the location of the tibial tunnel dictates the location of the femoral tunnel. Historically, we know that there are many instances where using trans-tibial drilling, the femoral tunnel was placed too vertically, which can lead to rotational instability. There's been obviously a huge focus on anatomic drilling of the femoral tunnel in the past several years and has led to the use of independent femoral tunnel drilling, oftentimes with an accessory intermedial portal. It is also possible to drill that tunnel independently using a retrograde drilling device. Preserving the ACL footprint can help you determine the appropriate location for the femoral tunnel and these over-the-top guides that we use. You want to use that such that you're preserving two millimeters of back wall. This is a cartoon diagram demonstrating the ideal position for the femoral tunnel. We see the lateral intercondylar ridge, which defines the anterior border of the ACL. These are some interoperative pictures showing the lateral intercondylar ridge as well as the bifurcate ridge, which divides the anteromedial and posterolateral bundles of the ACL. Just touching briefly, when you're on the steps to drill the femoral tunnel, you want to identify the starting point for the guide pin on the medial wall of the lateral femoral condyle with the knee in 90 degrees of flexion. That guide pin is directed ideally so it divides the anteromedial and posterolateral bundles. If you're using the accessory intermedial portal to drill this, you want to make sure to hyperflex the knee and then advance the pin out through the lateral aspect of the thigh. You then confirm appropriate placement of that pin. Absolutely, you want to check the placement of the pin and the tunnel, especially after you score the tunnel by viewing from the anteromedial portal, because what you see from that portal is quite different from what you see from the anterolateral portal. I have just a couple of pictures demonstrating here. On the left side, this is viewing from the anteromedial portal, and we're looking essentially straight up that tunnel. This tunnel was drilled with a plan for suspensory fixation. That's why you see that donut up at the top. On the right-hand side, you see the tunnel viewed from the anterolateral portal. It's really critical to view from both portals so you get an idea of what that looks like. For tibial tunnel placement, you can use both external and internal landmarks or intraarticular landmarks. Externally, you can use the anterior edge of the MCL, the superior border of the PES. Historically, the center of the ACL footprint has been used, and that has been defined as 43 percent of the A to P diameter of the tibial plateau. That was defined by a publication in 1994. Other studies have referenced seven millimeters anterior to the PCL in terms of placement of the tibial tunnel. Other studies have touched on using the posterior aspect of the anterior horn of the lateral meniscus as a reference point. This study was published in 2015, and the authors wanted to evaluate the accuracy and precision of the posterior border of the anterior horn of the lateral meniscus as an intraarticular landmark for tibial tunnel placement in single-bundle ACL reconstruction using independent femoral tunnel drilling. The authors hypothesized that the lateral meniscus would provide reproducible tibial tunnel locations as evaluated on an intraop lateral radiograph. They looked at 100 consecutive patients undergoing primary ACL reconstruction. The femoral tunnel was drilled using an accessory anteromedial portal. The guide pins for the tibial tunnel were placed using a 55-degree guide with the posterior border of the anterior horn of the lateral meniscus as a landmark, and then they obtained a true lateral fluoroscopic image after placing the pin. They found that the average AP distance achieved using that landmark was 37 percent. 66 percent of the tibial tunnels were located between 30 and 39 percent of the AP distance, and only 18 percent of the tunnels were localized between 40 and 45 percent, which was the area that was defined as the anatomic footprint in that study published in 1994. So therefore, the authors concluded that the use of the posterior border of the anterior horn of the lateral meniscus as a landmark for tibial tunnel placement during anatomic ACL reconstruction yields an inconsistent tunnel location. These are just some intraoperative pictures demonstrating the placement of the drill guide and its location or its proximity to the PCL. And then on the right-hand side, you can see the tibial tunnel looking down that tunnel. So in terms of graft fixation, absolutely, we want to make sure that it's strong enough to withstand closed-chain exercises for at least 12 weeks, that is, until bone and tendon incorporate into the bone tunnels. Closed-chain exercises produce about 200 to 500 newtons of force. In the case of poor fixation, the graft can slip, or in worst-case scenario, it leads to failure of fixation. So interference screws for patellar tendon bone block have the highest stiffness and fixation strength. The screw placement really needs to be placed parallel to the bone block, because when it diverges, you risk losing that fixation. The screw diameter and length absolutely influence fixation strength. For soft-tissue grafts, there are a lot of options. On the femoral side, we'll often use a suture button, that sort of suspensory fixation. On the tibial side, you can use an interference screw, or you could also use suspensory fixation, especially if you're using an all-inside technique. So some pearls and pitfalls. Patient positioning is absolutely critical, of course. We place a tourniquet. Oftentimes, we'll use a leg holder, which is shown in this picture here. We need to be able to flex the knee to 120 degrees, especially if you are using that accessory anteromedial portal for independent femoral tunnel drilling. In this case, the well leg is placed in the lithotomy boot, or you can place it in some other similar device to keep the leg out of the way. Other pearls. Of course, we know there are multiple graft options. We need to understand the pros and cons of each. When you're doing independent femoral tunnel drilling, you'll create this accessory medial portal. You need to remember to hyperflex the knee. One other little pearl to remove some of that debris that you develop as you're reaming. You can place a shaver in the standard anteromedial portal to remove debris as you're drilling from that accessory medial portal. Then when we fix the graft in the tibial tunnel, we'll place the knee. You can place it either in full extension or at about 20 to 30 degrees of flexion. Some pitfalls. Really, we need to make sure that we can visualize the femoral insertion site completely. Non-anatomic tunnel placement absolutely can lead to graft failure. We need to make sure we have a plan for alternative fixation options, especially if the posterior femoral cortex is violated. That fat pad sometimes can be quite robust, and if you don't debris that or remove that enough, that can interfere with your visualization, especially when you hyperflex the knee. Any questions, I'd be happy to address during the course.

ACL reconstruction

graft options

tunnel placement

fixation techniques

biomechanics

ACL grafts

graft fixation

autografts

allografts