Name: ACL Graft Fixation and the Next Generation
Uploaded: 2018-06-29T00:00:00Z
Channel: Arthrex
Description: Asheesh Bedi, MD, (Ann Arbor, MI) discusses the principles of ACL graft fixation, current science, trends, and the future of interference screws with FastThread™ BioComposite screws.

<p>Asheesh Bedi, MD, (Ann Arbor, MI) discusses the principles of ACL graft fixation, current science, trends, and the future of interference screws with FastThread™ BioComposite screws.</p>

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VPT1-01102-EN | A | ACL Graft Fixation and the Next Generation

Asheesh Bedi

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ACL Graft Fixation and the Next Generation

Well, today we're going to talk a little bit about ACL surgery and specifically graft fixation with the opportunity to talk about interference screw fixation and its evolution. I'm Asheesh Bedi from the University of Michigan and thanks for the opportunity to be here. I think all of us who do sports surgery enjoy the opportunity to do ACL reconstructions. And largely it's a very successful operation. More than 90% of our athletes typically get back to sport. But I think it's always our job as surgeons and our drive to always do better. And when we look at failure, it often falls into different types of categories. We tend to think of failure as a structurally torn graft, but as we look with a little bit more granular detail, we recognize sometimes failure is still an intact graft, but with functional instability for the athlete. And when you look in the literature at not returning to sport or the potential for associated meniscus injury after an ACL reconstruction, those numbers start to get higher, and that gives us an opportunity to continue to do better. I think all of us know when we look at what the most common reason is for an ACL failure, it's usually socket Malposition. Well, we know that when we place our tunnels in a non anatomic location, it doesn't make for a biomechanically or kinematically normal knee. And that's something that we have improved upon and certainly in 2018 feel comfortable with with a number of different options to perform relatively anatomic ACL reconstruction. The importance of this has been recognized. I think many of us have seen images like you see on on the screen here, vertical graft orientation. That gives good sagittal plane stability that we sometimes don't appreciate in stability on with a Lockman or a draw test. But these knees are still rotationally unstable and they still have residual pivot shifts with the athletes feel when they return back to cutting and twisting sport. Lots of credit to to my colleagues and and those before me, like Doctor Clancy and Doctor Fu and others who have taught us about the anatomy of the ACL. We now recognize this femoral attachment as this broad footprint on the lateral femoral condyle. The tibial attachment extending as anterior as the inner meniscal ligament, and the importance of placing our graft within the context of this footprint to to the best of our ability to restore the normal obliquity and alignment of the ACL. When we do these ACL reconstructions, or even when we scope knees in general, you can appreciate this anatomy. We've talked about posterolateral and anteromedial bundles, but perhaps the most important principle is that we have a continuity of these collagen fibers extending across a broad footprint to have a variable tension throughout functional range of motion of the knee. When we look at a multifaceted approach to improving our outcomes of ACL reconstruction, anatomy has been a large focus. But we don't want to forget some of these other principles. We know about occult instability and injuries to the anterolateral capsule, al and posterolateral corner. We recognize that even if we do everything correctly anatomically, sometimes the biology is against us, and tendon to bone healing reliably is a challenge, but we certainly don't want to forget about an opportunity for us to improve our outcomes as surgeons. And that specifically is this in this area of fixation. And that's what I want to focus on to a large degree today. Well, why should we care about fixation. And I wanted to highlight this paper that was done by Doctor Kurosaka and Andris years ago in our American Journal of Sports Medicine. And remember, they looked at different methods of fixation, fixating an ACL graft and the mechanical properties on the reconstructed ACL. And if you go back to this landmark article, as shown in these graphs, you see that the weakest region of the reconstructed graft is the fixation site. So let's not forget that when we finish our ACL reconstruction, that is our weak link and also our opportunity to have our best time zero fixation. So continuing to visit newer and different ways to perform reliable fixation for our grafts is worthwhile as surgeons. This is a paper from West in 2005 that points out the choice of choice of graph fixation even influences the risk of revision surgery after a primary ACL reconstruction with a soft tissue graft, and soft tissue grafts are probably particularly vulnerable rather than bone to bone fixation, which is typical for our orthopedic principles from trauma and and surgery. We recognize that soft tissue grafts offer additional challenges. This is a paper from Thor Zantop and Wolf Petersen from Germany, where they looked again at fixation. They wanted to compare the structural properties of interference screw constructs for soft tissue grafts, and also visit a very important principle. What damage do we potentially do to the graft when we insert an interference screw? And I'll highlight the important principles here, which is that their studies show that a titanium screw to fix a soft tissue graft did cause damage to the graft. And in fact, paying attention to this at the time of surgery is critically important because we don't have the benefit of second look surgeries or sometimes outcomes down the road where we can explain this from time zero injury related to our fixation. It's another study that you'll see here that, again visits this issue. And it highlights the fact that graph laceration or pull out slippage at time zero is a concern with soft tissue grafts in their study. What they ended up finding was that insertion of interference screws did fundamentally alter the biomechanical properties of the graft itself. It decreased yield load ultimate load stiffness when compared to a native graft. So once again, inserting an interference screw with a soft tissue graft may not be benign. And for us to do this right, we need all the right principles and all the right aspects of our screw to get this correct. So what is the ideal interference screw? And I would argue these are the principles that I look for and that all of us look for. We want it to be easy and reliable. We want good bone stock. We want it to be as strong as possible the day we do it in the O.R. ideally, we want the screw to hang around long enough, if you will, to have time. Zero biomechanical strength, but also reliably become part of the bone without a foreign body Reaction. We want to avoid damaging our graph, putting it in. And maybe as we realize the importance of biologic augmentation in the future, we may want it as a vehicle to deliver a biological augments. And certainly we also want it to be safe and cost effective. So that's gives us the opportunity to talk about how screws have changed over time. And all of us would recognize this kind of migration as we've looked at metal screws to now more modern bio composite screws. Well, if you look here, the metal screws, they did meet the mark with regard to being relatively easy to put in and being strong, but they offered some challenges as we talked about in our previous papers. They can abrade or damage the graft. They can cause some artifact. When we look for second time imaging. And as we know, these can be problematic at the time of a second surgery, both with removal but also loss of bone stock as these evolved. We moved to to first generation biocomposite screws. These are improved by having no MRI scanner. They facilitated revisions because they could they could either be easily removed or drilled through at the time of a revision surgery. But these weren't necessarily the best in terms of our time. Zero strength. They could break, they could slip, and we knew that there was improvements in materials that could have great time. Zero biomechanical strength, but be osteoconductive and have all the best of both worlds. Our most modern PLA material combined with calcium phosphate can accomplish those goals. So in some ways, as you look at the evolution, what our goal is, is to retain all of the good and get rid of all the bad so that we can ideally have time, zero fixation, good incorporation, and avoid any injury to our graft. Well, that brings us to the FastThread screw, which is our most modern design to incorporate these principles. As we've already talked about, we want it to go in reliably and reasonably quickly. We want enough material that offers a good scaffold for healing, but we don't want too much material to create voids and problems, potentially for revision surgery. We want them to be strong, to optimize our time. Zero biomechanical Mechanical strength, but we also want to avoid any potential for injury or laceration to our graft. And if we optimize these principles combined with a solid clinical history and outcomes, then I think we have put together most of the optimal elements that we need for good time. Zero fixation at surgery. Well, let's talk about some of those principles. The FastThread engages quickly, and it begins to advance with minimal turns. As you can see here, some specific design related to the pitch and the threads allows this to happen relatively easily. As you can also notice, they have these vents, which we'll talk about shortly, which facilitate ingrowth for for bone and also potential venting for delivery of biologics. This speaks a little bit to that larger pitch thread that you can see here. Compared to our conventional biocomposite screw, it takes less turns of the screw driver to advance antegrade. It allows for faster insertion, but importantly, it allows for more interdigitation of the graft between these threads. That prominent lead thread for advancement of the graft allows this to advance reliably. Note that it's very strong when it's compared here to some of our other historical biocomposite screws, even some of those that are the standard of care on the market. It has improved strength with a shorter length. You can see that likely reflects this difference between the pitch and the thread. And this opportunity for graft interdigitation, which increases the interface for friction without damage to the graft, as you can see here. We've done some torque testing of the FastThread screw. Really put this to the test in hard porcine bone. In this particular worst case scenario model, we have not tapped the bone. This is an undersized socket and I think you can appreciate this is able to be advanced reliably with secure fixation in bone. One of the important principles that all of us have seen in the past is sometimes with our bio composite screws, we fear that they are deforming or losing their fixation strength as they go in. In this particular case, we actually remove the screw and can appreciate that it has preserved its thread geometry and preserved its form to maximize that time. Zero strength in bone. So again, ease of ease of placement and solid time zero fixation. The mechanism to place these screws with this fully cannulated hex driver is unique. As you have seen, this mechanism allows for the screw to be supported along the entire length. This is important with biocomposite screws so that the screw is not subject to a torque with a short driver and and put at risk for breaking. This hex drive also allows for a central area void of graft material or of screw material. So it allows for again excellent ingrowth from the vents in the screw itself. So as we mentioned earlier, one of the primary and very important principles guiding interference fixation, particularly with soft tissue grafts, but also for bone tendon bone grafts is to protect our graft and the soft tissue interface. You can see this design of the FastThread is key to this. The threads themselves are rounded, so they really avoid graft, laceration and damage. As you can see, the head is rounded, so particularly as you advance the Advance the graft and advance the screw to the final few turns of fixation. It offers less risk of laceration. This graft protective sheath is also available. Many of us consider using this, particularly as we place our femoral screw with bone-tendon-bone grafts. And this is yet one more additional point to protect your graft with placement as we move forward. Here again, we talked about material. It's important to have sufficient material that provides time zero fixation. But we really like to minimize the amount of material we have to permit ingrowth to be osteoconductive, and also to plan for the rainy day at the time of a potential revision ACL. As you can see here, the FastThread accomplishes this by actually being 22% less material than the previous Biocomposite screw. You can see this allows for a maximum interface for healing. It still preserves opportunity for biologic delivery through our vents, but again preserves bone stock for for future cases. In terms of what's available as we we are aware in the In the bone-tendon-bone situation, we typically have sockets, sometimes as small as six seven eight millimeters, but as large as ten and 11mm. These are 20 millimeter screw lengths that are available, which are a good match for your typical bone plug and ideal for your BTB fixation on the soft tissue side or on the tibial side of a BTB graft. We have 7 to 12 millimeter sizes. These come both in a 23 and a 30 millimeter length. And again, that's ideal for soft tissue and patellar tendon graft fixation. And any place where you might have a little bit longer socket. In my practice, sometimes with mpfl reconstruction or any place that I'm docking a soft tissue graft. Well, what is the material? We talked about the importance of having something that has hangs around long enough, if you will, for good time. Zero fixation, but also has a reliable track record of Osseointegration. And the biocomposite material is a combination of 70% ldla and 30% calcium phosphate. And we found this to have a very reliable and long track record of safety, but also a reliable track record of incorporating into the bone. This has been studied very reliably in the laboratory, as you can see here. The clinical history is over 1.3 million screws implanted over the past 12 years, with a less than 0.002% complaint rate of issues. So largely speaking, as we discussed, we certainly don't want foreign body reactions or concerns related to a sterile inflammatory reaction with biocomposite devices and over 1 million implantation. With this 70% 30% balance of material gives us a lot of confidence that that we don't have this issue. We also have very good animal and translational research models that demonstrate the favorable osseointegration of these FastThread screws and biocomposite material. You can see here this is 52 week or one year data in a Goat model. These are soft tissue ACL reconstructions that are performed with the Arthrex FastThread screw versus a comparable material. I think you can appreciate this favorable osseointegration. The screw and its associated track and tunnel are largely incorporated with woven bone that is subsequently maturing into into a native mature bone. We subsequently had even the opportunity for a two year data. I think, again, you can appreciate here no foreign body reaction on Micro-ct and CT data, excellent incorporation and essentially full bone stock such that should a revision ACL reconstruction be necessary, you really have no concern over voids or the need for a potentially staged procedure. This is actually perhaps what is even more exciting about these FastThread screws. You can see this is a dog model, a dog tibia and femur. Here at 16 weeks out, I think you can appreciate these vents and the FastThread screws. This has allowed for bony ingrowth into those screw vents. This essentially starts to create these bridges that are right across your screw and interface construct. These might not only contribute to mechanical strength, but once again contribute to our goal of of preserving bone and minimizing foreign material. So again another strength and opportunity with with this fixation. So to summarize here, I think the FastThread screw represents really the amalgamation of all the favorable aspects as we've evolved interference fixation. It's a reliable material with over 1 million implanted. It's 22% less material in the tunnel. It's easily inserted and reliably inserted. It's strong. And again, when we when we highlighted earlier today what is our real criteria of ideal interference screw fixation I think it meets the mark. It preserves bone stock, has great time zero properties, avoids laceration and damage of the graft. And as we launch into the future with with understanding the appropriate delivery of biologics, it offers us that opportunity to do so at the most important interface of our ACL reconstructions, namely the tendon bone interface and the interface of the graft in the socket. So thanks again for the opportunity to speak with you about this today.

ACL Graft Fixation and the Next Generation

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