Well, I thought I had a bit of a hard topic, but David just took us through a wonderful quick summary of very complex patellofemoral. Mine may not be so that complex, and you'll probably see this every day. So as we have learned already today, the four principle of patellofemoral instability factors that were founded in anatomy came from the Lyon School, and that was trochlear dysplasia, a high Q vector as demonstrated by a TTTG, lateral patella tilt, and patella alta as evidenced by Canton-Deschamps. And the Lyon method was a surgical correction where they tried to correct each factor when it was present. And in fact, they did quite well, and this still stands as a very large cohort where they had 1% recurrence, but it was without an MPFL. And so the question is, where are we now? Does the menu still make sense? And we do know a few things, that we know what a first-time patella dislocator looks like. We know that when we know how to look at the anatomy of that first-time patella dislocator. These are just two studies. There are several out there. And we do know that a high TTTG in isolation is less represented, and that patella alta and trochlear dysplasia predominate. The thing that's important to understand, and this is what we've heard Jupiter and others are trying to find the holy grail. We do know what anatomic factors are present when you have an increased risk factor for both primary and recurrent dislocations. But we don't know when these factors have to be surgically corrected or at what threshold for optimal results. Now when you talk about the tibiotubal osteotomy, it really can be a workhorse for patellofemoral. You can have medial transfer, anterior, anterior medial, or distal transfer. A brief historical perspective. The anterior transfer started with the Bandy-McKay procedure, which was to treat pain, or the Elmsley-Triat procedure, which was to treat instability. And then the anterior medialization, which has been coined in the United States as a focus on osteotomy, by his own words was to treat persistent patellofemoral arthritis. And this combined an anterior medialization without the need to both cut through the block when you're medializing it. Now we've also learned from John Fulkerson and his cohorts that this is mainly an unloading operation and it is best done. Of course, you shift the load. It is best done when your load is either inferior, which is common, or lateral, which is common. So how much should we try to be moving this? Well the original McKay procedure described 20-25 millimeters. And I'm happy to say I wasn't quite old enough to have done this, but I did a few in my early years. And they did have some skin problems. Fulkerson did a mathematical calculation and felt that you could unload it with less millimeters, 12.5 millimeters. The AMZ is a workhorse, but it's a little bit confusing in what actually happens when you move it anteriorly and medially. So if you remember your algorithm that you can look at the amount of anterior displacement. And just to give you an idea of if you know your math, with a 60-degree slope and 9 millimeters of medialization, that anterior, straight anterior displacement is about 15 millimeters. And so that really is getting up to where we might have some potential skin problems. So just to kind of keep that in mind. So when do I consider an AMZ? For me, for sure, an AMZ is an unloading operation. So you have to start with people who need their patella unloaded, particularly when it's inferior and lateral. I think that this is a good operation when you also have some early tibial femoral OA, but you're not yet a TKA candidate and possibly not a patella femoral arthroplasty candidate either because of early tibial femoral disease. It's preferable that you do have a high TTTG because the angle that you need to get to have anterior displacement when you don't have a high TTTG tends to encroach potential problems with healing and potential problems with skin. And I also feel that when you don't have lateral tightness, i.e. you don't have any lateral tightness to release, it becomes a workhorse. But if you do have tightness, sometimes when you have early arthritis, a lateral fascitectomy and an LRL will buy that patient some years. So when do you perform a straight tibial tubercle medialization? Now we did learn from Jay Cox and the other people at West Point that when you do an Elmslie triot and you just elevate it a little bit, about 15 degrees above the level of the horizon, that is actually the Elmslie triot. And when you do an anterior medialization, it's a longer slab. It's a longer bony tibial tubercle slab. And your goal is to have more slope and to have more anteriorization. So I'm talking about a tibial tubercle straight medialization which may have about a 15-degree anteriorization. Now this is for patella realignment surgery when you believe that you have an elevated TTTG. This has been our workhorse. Here's the problem. What makes up that TTTG measurement? Well, it's three things. One is the lateralization of the tibial tubercle, the rotation between the femur and tibia, and the medialization of the trochlear groove. Now we do know in our literature, it's been here now for at least seven years, that we have lateralization that we can measure and it's about 40-60%, so 60% medial to the medial border of the cortex on the tibia, the anterior tibia. But here's what I think that we missed. There is a significant amount of rotation between the femur and the tibia. If you look at these reports, Setender, when he said his PT-PCL, which was 2012, he showed us that you can have up to 20 degrees of rotation. But I think that it really never settled into our consciousness how much this was really interfering with our measurements of TTTG, so that you can see that there's a fair amount of rotation. And then the last is with high-grade trochlear dysplasia, since you know that that medial trochlear is elevated, forcing your sulcus, defined as the lowest point, more medial, that you can have a high TTTG because your proximal number is more medial, as evidenced in this CT scan. So I think that we just have to be aware that this TTTG distance may not be the number that we should be looking towards in trying to make some decisions. We do know that the lateralization of the tibial tubercle when you just measure it on the proximal tibia is not greater in a patellofemoral dislocation compared to controls. We also know that knee rotation in a patellofemoral dislocation group is greater than controls, although I do think these studies are hard to standardize. And we have shown some studies that the TTTG distance was more affected by knee rotation and less so by tibial tubercle offset or trochlear groove medialization. So I just think we have to keep in mind and perhaps that TTTG is not what we should look for and perhaps that the TTT, the overlap of the patella tendon is what we need to look at. So we also have several studies in the literature that have done studies where they have ignored the measurement of the TTTG, have just done an MPFL and have done well. We also have the study by Marchuto and others in 2014 that was a very small but nicely done randomized controlled study where they ignored the TTTG in one group and if they were greater than 20 only did an MPFL or if it was greater than 20 they medialized it and they had the same dislocation rate which was 0, same clinical score between the two groups. So I think that we're coming to depend on that medialization less. So a TTTG distance of greater than 20 may not be an absolute indication. And I think that we have to look towards other things. And we do know how important the trochlear groove morphology is and the general alignment of that leg. I also want to say something about the Q vector. The Q vector is somewhat determinate by your screw hole mechanism and full extension. And when you bend that knee up and if you see on your left, no I'm sorry, yeah your left, you can have a sitting Q angle. Now some people call this the tubal sulcus angle, sometimes people call it a sitting Q angle, but ideally we want that tibial tubercle to be directly in the middle. If you have a tubal sulcus angle of 0, regardless of what your Q angle is, and you medialize it, you're going to potentially create medial patellofemoral forces as well as medial tibial femoral forces. And we do have one clinical study and one anatomic study that does demonstrate this. So I do think that when you're going to medialize the TTTG, regardless of where you're starting, you should aim for an interoperative measurement of 0, meaning that you put it right underneath the middle of the sulcus with the knee flexed. And you can mark that because of course it's hard to fix it at 90 degrees, but that's what you should be aiming for. So when do I medialize the tibial tubercle with an MPFL for patellar stabilization? Well, I will admit that it's rare in my practice for recurrent instability without overload. I think that there should be no tightness laterally because I can't release or lengthen anything. And with a distalization, when I do a distalization, I always move my tibial tubercle to a tubal sulcus angle of 0, which ends up being about 80% of the distalizations that I do. So it's not that I don't do them, but I rarely do them in isolation. So the last one is the distalization of the tibial tubercle, which I think is the workhorse for patellar stabilization. We have mostly used the trilateral x-ray on plane radiographs. And for the patellofemoral world, both in Selsovati and Canton de Chance have been our workhorses. And this is still good, but you can't use one measurement. And that's why I think anybody that's looking for an algorithm with one measurement, you're just going to have some problems that you run into. For instance, here with that very long nose, you have an IS that's reasonable, you have a Canton de Chance that's high. And so we did learn from Roley Biedert that what you really want to look at is that engagement with the femur, or what you might call functional engagement, which compares the overlap of the cartilage between the patella and the trochlea. Although ideally, this is absolutely what we'd like to see. It's very hard to get on an MRI, and if you're going to be looking for the cartilage, an MRI would be the best way to look at that. So we do know from Roley Biedert, in a fairly small cohort, that he described ALTA as less than 0.125, which is about a one-eighth overlap, which isn't very much. And I was looking towards a couple of studies that looked at population cohorts. This was one that was actually a Don Fithian study, Charles is the first author. And he had a fairly decent cohort, and he showed that normal was just a little bit less than 50%. So I'm looking for maybe a one-third overlap as saying that that's good, so 20% to 35%. And here it shows you the problem. You want to take that measurement where you see in the center of the knee where you see the cruciate, but oftentimes the patella is lateralized. And so it's hard to get that patella and that central groove in the same plane. What I like to also look at is a qualitative measurement that if you're looking at your axial images, you look at that first cartilage slice. The first axial slice with full cartilage coverage, and you look up and you see the patella tendon. So you know there qualitatively you have patella ALTA, even though you need other things to measure and make your operative decision-making. I also want to call out hyperextension. For those of you guys that know me, this is kind of something that I think I overlooked in my early days. I think that you cannot correct hyperextension easily. It's got to include quad control and terminal extension, which is part of your brain, part of what your therapist does. You could consider bracing against terminal hyperextension, but this really is functional ALTA. You contract your quad, you hyperextend your knee, that's a really hard patella to keep in control as you go back into flexion. And I do lower my surgical threshold for distalizing TTO when I have knee hyperextension. Just one quick clinical case. Here we see decision-making, I do use everything, canton de chance was 1.2, IS was 1.4. Really shallow sulcus, but not convex. Patella trochlear index was practically zero. You can see the overlap of the patella tendon on the lateral quad. The trochlear depth, again, was not convex, two millimeters shallow, but not convex, and you see the empty sulcus sign. In the operating room, I went in with the plan for TTO distalizing, but I just picked up a clamp on my patella, I pulled it up, took an image, and to me this is trying to duplicate what the quad is doing. And you can see that even though you don't see cartilage, that the cartilage of the patella is above the cartilage of the trochlea. So this person did get a MPFL with the distalization. So when do I distalize it? I will say that I still use a canton de chance of 1.4 as just sort of a starting point. But I also look at functional engagement of around 15%. The problem with just looking at one number is that we don't have a good way to measure the length of the trochlea. And most of our descriptions for trochlear dysplasia doesn't include a length. When you have a J sign with patella alta, as David's already indicated, sometimes we can bypass the bump. And those are sort of more hard signs that I have in bold. But I begin to think about it when both knees have instability, again when you have knee hyperextension greater than 10 degrees, and when your ADLs are affected, when people are standing at a sink and turning around, or in a shower and turning around and they dislocate. So really functional problems, I think they need more than a soft tissue reconstruction. So in summary, I still believe, although I do very few medializations, that the tibial tubercle osteotomy remains a powerful tool in the surgical algorithm for patella stabilization. Don't rely on a single number for either tibial tubercle lateralization or patella alta. The menu has morphed. We continue to learn. And I certainly have great younger people that will carry on this work. Thank you.

patellofemoral instability

surgical correction

Lyon School

tibial tubercle osteotomy

patella stabilization