So, let me go back one slide because I want to introduce this. So this is a test that I think is really useful. I don't see it described much. I call it the moving apprehension test. Somebody has a more proper name, let me know. But when you're trying to assess degrees of instability and make decisions, or when you're trying to sort out, is this instability or is this pain-related buckling, right? You see that patient sometimes who's got, when does it dislocate? Well, it's on stairs. You're like, wait a minute, that may not be true instability. Maybe their body habitus makes it a little bit more difficult. Maybe they're really queasy about you touching their patella. So this is a moving apprehension test with a quad relaxed, completely relaxed. You try to translate the patella laterally as you slowly flex the knee, and you find at what degree of flexion does it lock in, or you can't move it, okay? So this is a very, very fit individual. But you can just move it sideways, and it can move just a little bit. And you say, okay, when does it lock in? And basically, the greater degree of flexion where it locks in, the more is going on. Simple as that. And probably the more you have to do in a simple-minded way. And the other side has been fixed, and typically by 30 degrees with a stable knee, it locks in. And I will tell you, for that differentiation of buckling versus instability, this is incredibly useful, where they've referred the patient to you, they think they're unstable, the family's fixed on unstable, and you show them this and say, listen, your patella's not dislocating. We really got to get your quad stronger to get your pain better. Very, very useful, and also very helpful for making decisions. So here's a patient, also skeletally immature, 12 years of age, two true dislocations, multiple subluxations, premenarchal, so very young, extremely apprehensive, very hyperlaxed. She just had a recent subluxation, she's effusing. And she, you can translate the patella all the way up to 90 degrees. You can still move it laterally some, all the way up to 90 degrees. So here's the imaging, FIC's wide open. The sunrise view is obviously too flexed. You should only see down to the epicondyles. If you see more femur, you're flexed way too much. It's a rare case where anything's going on that you're going to see on a sunrise view at 90 degrees of flexion, useless x-ray, okay? If you're taking x-rays like this, I encourage you, make sure you get them at 45 degrees at the most of flexion to really understand the anatomy. I'm going to show you a bit later with the trochlear dysplasia case that even that doesn't tell you as much as you want to know about the trochlea. So here's the MRI, TTTG of 10, not high at all. PTLTR, I actually use this number quite a bit. So you can see the amount of tendons. So how do you do this? It's perpendicular to the posterior condyles, then take it up to the apex here, and then you measure in the middle. More than five and a half is abnormal, but it just visually makes sense. I mean, I'm thinking about what's the vector that's pulling this patella. So here's a great example. That's a high PTLTR, and as Sabrina pointed out, you can have soft tissue irritation, fat pad irritation, but the TTTG is normal. So what's going on? Well, in this case, it's patella alta. So the higher that patella sits, because the femurs can be relatively round and somebody have a little bit of valgus alignment, the patella can sit laterally in its resting position, and it's a setup to dislocate, but yet the TTTG is not the problem. So I pay a lot of attention to the PTLTR as an indication, well, I got to think about the vector, but it's not just because of a lateralized tubercle. So with alta or a little valgus, you'll often have a high PTLTR with a normal TTTG. So I actually measure this in everybody. Every patella instability patient comes in, I measure the PTLTR, the TTTG, the CD ratio, and I've also gone to getting long-standing alignment films on everybody. I used to think I could eyeball this, especially if the body habitus is not a problem. I thought I could eyeball it, then send them for the long-standing x-rays. I found I cannot. So I get that all the time, and these growing kids is a great opportunity for guided growth, to put one of those figure-of-eight plates across the physis and let them grow if they've got more growth remaining. It's such a benign operation, and I've gone to being much more aggressive with my PEDS colleagues for doing that. If they're like four, five, six of valgus, it's a great opportunity to change it. But here's the punchline of this case, is that CD ratio is 1.6. This is really, really high, okay? So the kid is still growing, you can't move the tubercle. And this case kind of highlights, wow, maybe that would have been a good thing to do to change some anatomic risk factor there. So here's a way you can do it while they're still growing. You can shorten the patella tendon. And this may be a little much to digest in these slides, but Jack Andrus has really written some good stuff, and there's a great technique paper. This is OJSM. I'm going to walk you through it. But you basically expose the tendon and get working space behind it. And then we're going to draw a line. So we measured how much we needed to dislice the patella to get an end result CD ratio of 1.1. That's my target, okay? 13 millimeters was the answer. So those are the two darker blue lines. And then you go above that, half that distance, okay? So that's my shortening desired amount, and that's half that distance up there, and you mark it out. And then you start to feather the patella tendon in half, which sounds ridiculous, but it actually works. And I'm going to show you how you would get a very robust repair at the end. You take a 15 blade and you just feather it across there up to that point of desired shortening like this. And then you mark the midpoint of that because you're going to fold it inside. You're going to fold it inside on itself, and then you place these vicral sutures. So the sutures are going to come through here, and they're going to exit out up top at the other line so that when you pucker it inside, they're going to fold up to itself. So there you see the vicral sutures exiting at the top. They've come in through here and exit up there. So come in here underneath the tendon, out, across the top, underneath the tendon, and out so that they'll pucker inside. And then you take another set of sutures, and these are nonabsorbable sutures, and you enter from this line here, come across the front, and through this part of the bottom, there's a suture here, a suture here, across the front, and out. So you have another set of sutures. And then you pull it up so that you fold it in on itself like this, and it doubles the layer, and then you tie the sutures down, and then lastly, you tack it down on the top, and you get this very thick patella tendon when you're done. So it's not scary when you're done. It's scary as you feather it, but when you're done, you realize, well, that's really strong. And this works. This works very well. So I've done a handful of these. Then I do the NPFL. So this is getting shallow's point. Notice, it looks like on the lateral, you're going to go straight through the physis, but remember, it's a smiley face. You will not. The physis on the medial margin is going up, of course, but you do have to be aware of the back of the femur. So what I'll do is when I find my spot, shallow's point here, I'll then put a clamp on the same up there, I'll put a clamp here at my target point, so it gives me a visual as I aim across with the pen, and I'll drill right to there. It really helps your hand-eye coordination to hit that target. Then you're all epiphyseal, and then I will put a screw in. I may drill a smaller tunnel. I may drill just a six, but that works really well. And Jack has published on this with a large number of patients, and you don't lose your correction. So this imprecation technique holds up. It doesn't stretch out. It's very reliable. So when you get those rare patients that have extreme ALTA, this is a great way to do it. Any questions on that case? My trigger is 1.4. 1.4 CD ratio and multiple instability events. Then I would probably think about doing this. This was, I mean, 1.6 is extreme. Yeah? No problem getting flexion. No problem getting flexion whatsoever. So I treat them the same way I would any kind of a bony procedure plus NPFL. 50% weight bearing for the first six weeks. I go 0 to 70 on the brace the first two weeks, then 0 to 90. But stretching out isn't an issue. Other questions? Yeah? That's right. You're just folding it in on itself and suturing it underneath. Yeah. The paper, you know, for me, I have to sit down and look at it before I do these cases each time. But this is a really good paper he's written, Jack Andrish. Yeah? So the sutures act to create the fold. It kind of puckers it inside and then brings it up underneath and then it's tied down. And then the other one's pulled on top. Yeah? Yeah. Yeah. Yeah, exactly. And then the thinner layer comes down on top. Yeah. So it's almost tripled when you're done. Yeah? Excellent point. One other thing we've learned is if you do a two-tailed MPFL graft, that will also bring your patella down by 0.1. So you can factor that into your math. Yeah? Yeah, good question. And it also relates to these other cases if you have bad dysplasia. But I will treat them just like I would an ACL. The decision-making, when we look at an x-ray, we look at the fysis and say, they're closing, they're beginning to close. I think a BTB or just a transfisial tunnel would be okay. Then I just feel free to do bony work. I treat them exactly that same way. So this first case just kind of helps, I think, get a working understanding of dysplasia and for decision-making. So the de jure classification is descriptive. These are shapes. It doesn't guide decision-making necessarily. Bs and Ds are the ones with a prominence where you may have an opportunity and something to consider. Ds can have a cliff sign, as you see there. But don't be glued to this as the way you're thinking about decisions. I'm going to try to make this as simple as I can. And I think it's really about convexity and how large this bump is and whether this bump is truly influencing the patella and something has to be done or not. So here's, again, another sunrise view two-flexed. You should only see to the epicondyles for an accurate view. And as you can see, that trochlea looks very unimpressive. But I go straight to the lateral view. And if I see a prominence that sits anterior to the femoral shaft, I know I need three-dimensional imaging. So I know I need an MRI to really understand what's going on there and where the patella articulates. So there's a long-standing view. That's not a problem. But that prominence is. So here's a lateral view. And you take the blue incised line coming out of the notch. And where that continues is the base of the groove. That's the orange line on the left. And then you follow that up. And then you take the lateral femoral condyle. That's the blue line. And where they meet, it's at the same height. So now that's flat, and that is called a crossing sign because they're at the same level. And if it continues further anteriorly, which are the yellow dots, that is a prominence. It's also been called a bump. It's also been called a spur. I think a spur is misleading because it sounds like you could just knock it off with an osteotome. That doesn't fix this problem. But this continues anteriorly. And this should be, in a normal knee, flush with the anterior femoral cortex. The base of the groove should be. So all that is extra bone sitting in the front. Now, in a knee that has bad dysplasia with that cliff sign, so that lateral side is up and convex, the medial side of the trochlea is really hypoplastic and sits much lower, and that's the double contour. So that's these orange dots, this other line here. So that's sitting low, and the lateral side is sitting way up high, and that's the convexity. And that's this kind of a shape, okay? So you get this really convex surface, and then it drops off, and the medial side is hypoplastic. So when I see that convex shape that sits way in front of the femur, then I'm thinking maybe I need to do something about this, especially to have a big jumping J sign. If they have enough alta that I'm going to be distalizing it a significant amount, then I can maybe get past this into a more normal, at least flat trochlea. Flat trochlea doesn't matter. Flat is fine. You can balance it. You can fix these, even with a little convexity. But when it's convex like that, that's going to be a problem, and that's going to really lead to anything else you do to potentially fail, okay, and continue to have a jumping J sign. I'm going to highlight that with my last case. But you want that to be when you're done. This is post-trochleoplasty, flush with the anterofemal cortex. So let's talk about this and vectors, okay? This patient is a typical one where I'll see and consider trochlear work. 15-year-old, bilateral issues, started at age 8. The younger they start, the more is going on because as they're growing, their patella is tracking poorly, and I think that's how you develop dysplasia. I don't think you're born with it. I think you're born with maltracking, and then it develops. Dan Green at this meeting showed a couple of very interesting cases with very young kids where he centered the patella and then showed the trochlea then basically remodel and correct dysplasia. So that's what I think happens when people get dysplastic. Somehow this kid was athletic, which is rare. They usually can't do anything. They're often very affected. Big jumping J sign every time they extended their knee. Very apprehensive. And so normal alignment, but look at that prominence on the lateral view. So when you get, there's the crossing sign, there's that prominence sitting in front of the femur, and there's a double contour. Oh, but look at that sunrise view. Completely unimpressive, right? You learn very little from that sunrise view. It's really about the lateral x-ray, then you've got to go to three-dimensional imaging, and then you see this. And this is an incredible convexity. So I would offer that anything less than trochleoplasty is doomed to fail in this patient. So, boy, it's tough with these lights. But the orange dots are the actual contour of the femur. So that is how prominent and convex it is. And you get that pseudo-articulation on this side, and you see how lateral the patella will sit, too. So this one was 9 millimeters in front of the femur. When you go to the slice with the cruciates, that should be the lowest point of the groove. And you see how much sits in front of bone plus cartilage. They don't have alta, so there's not an opportunity to move it distal enough to get past this area. The TTTG was elevated, but the PTLTR is also very elevated because that thing sits lateral to this. So in my simple-minded understanding, the lateral vector has caused the patella to track over there, has created the dysplasia, and I've got to think about correcting that, too. So this is how you can also look at vector's effect. So look at this knee with jumping J sign asleep. It was at 90 degrees before it popped back in, so with external rotation on the foot. Now if I correct the vector, internally rotate the foot, the patella tracks centrally all the way up. You can do this in the office with somebody, too. You can also have them hanging off the table and internally rotate their foot and demonstrate a more dramatic J sign as you extend the knee. One more time. So the foot is externally rotated, the patella is out. Now it's back in. Thank you. And then internal rotation corrects it. That just reaffirms to me that the vector's an issue. I need to change it. So when do I think about, in this whole ICL, when do we think we need to do something to change the bony anatomy, these anatomic risk factors? So here's a very good systematic review, 17 studies. It looks at all the different anatomic risk factors. So if you pick one in isolation, you have elevated odds ratio, but that doesn't really tell you which one you have to change. But I think instead think about, well, what happens if these work in combination? And as you see, if you've got three anatomic risk factors, you've got a 75% risk of recurrent instability. So if all I do is correct the NPFL and fix that, they've still got potentially a very high risk of continued instability, and that's why these people have bilateral instability. So the more anatomic risk factors a person has, the more I think I've got to change the anatomy. And I'm pretty aggressive with osteotomies. But when I see multiple ones together, that's kind of my trigger to say I've got to change something. Now what's the dominant risk factor? What's really driving this vector? Is it ALTA or whatever? So here's another study on the left that shows those that had an isolated NPFL and failed, what was the key factor there? And it's greater than two anatomic risk factors. So it's, again, multiple anatomic risk factors together that guide you to say, hmm, I've got to do something more. So this patient has at least four. So anatomic risk factors, dysplasia, ALTA, malalignment, and open physis is another one, actually, anatomic risk factor. She started at age eight. So four, I'm like telling the family, and if this was a first-time dislocator, I'd tell the family, listen, at least 75% chance you're going to have more dislocations. You're at risk for cartilage injury. We should do something now. That would be my message to the family. So I'm going to change that vector, and I'm also going to change the trochlea. So when I got in there, you can see in this poor teenager, terrible cartilage damage from recurrent instability, loose bodies, cartilage lesion. I just debrided it. I tend to not be very aggressive with cartilage procedures with instability because most of the lesions occur from reentry, as opposed to wear, and once you stabilize the patella, they're not very symptomatic, and they're not loading that inferior medial part of the patella, which is reentry, the same way, or that lateral ridge of the trochlea the same way. So in this case, just debrided it, and the spur was even larger in the OR. I think it was like 11 anterior to the femoral shaft. This femoral shaft is underneath the osteotome, and we undermine it, drop it down, crease it in the middle, and reshape it and hold it there with vicral sutures. So the general gestalt for that is it's convex like this. The dotted lines are where it's going to kind of bend. The solid line in the middle is where I crease it with a 20 blade, and just on that lateral edge, I crease it partway there so you don't have a free shingle, and then the yellow lines are the sutures that are going to reshape it after I pull it down. And this is post-op. So here I moved her distally slightly on the tubercle. I used three screws, 4.5 cortical screws with a low profile head. The middle one I put at a different angle off axis. Sometimes you'll get a fracture in that cortex distally, and it'll want to keep on propagating up to that other screw. So if I put the other one off axis, the split doesn't do a zigzag. It really behaves like a block of wood would. So that's why you see that middle one at a different angle. And I've seen my union rates be more predictable. I have less delayed unions with that with a third screw, I find. And I'll do an overlap like this if I'm going less than a centimeter distal. If it's greater than a centimeter distal, I will do a step cut with a bone block transfer. And there you see the sunrise view and the trochlea post-op. So most important to me when I look at these post-ops is that lateral x-ray. And I draw the line down the anterofemoral shaft and think about the base of the groove. That's the real goal is to get rid of that prominence and the convexity and at least make it flat. You don't create a lot of depth. It's really getting rid of the convex prominence that you're doing here. Questions about this case? Yeah, yeah. In the setting of trochleoplasty, some techniques, you can medialize your groove and then you get away with the lateral. I mean, we usually don't associate the distal realignment. If you do a lateral rectangle, Anthony, and then you can fail. How do you see that? Do you always do your medialization when you have the lateral vector associated with the trochleoplasty? Yeah. Or in some cases, you can medialize and get away with all the distal. Yeah. So the question, this is a good one. The question is actually, it's actually lateralizing the groove. So if your TTTG, right, your groove is here and your tubercle's sitting over here, you can reduce that number by lateralizing your groove and your TTTG is less, right? But can you maybe do that instead of moving the tubercle over? And I used to think that, but I don't think that anymore because I don't really think the trochlea gives you containment. And I'm gonna show you a great case about that. So for me, I'm really thinking about moving it distally and changing the vector and the pull of the muscles down there. And I also don't think that trying to change that shape of the groove changes it much. The native groove with a really dysplastic trochlea is actually pointed medial. And it's very short and it's going in a direction that the patella can never get to. The patella's trying to track like this and the native groove is over here. It never can go over there and do this. So it's sitting on the convex surface and that's why it jumps all the time. So you're really creating a new place for it. You're not using the existing groove that goes that way at all. You find it at the bottom, the depth of the groove distally, and from that point you're going up along basically right in line with the shaft of the femur, which should be the muscle pull. Now that's where I'm gonna put the new groove. Does that help? Yeah. Yeah, I think probably we understand torsion least well about these patellofemoral cases. So like this patient, they often have a little of everything for risk factors, but I tend to be least aggressive with torsion. If I see it and I examine them, get them prone, do those tests, then I may get a CT. I worry a little bit about radiation, so I'm not getting those infrequently, but if they're very rotated, like 40, 35, 40, then I'm thinking about rotation, but that's a rare case. We don't have a rotation case. Oh, we do? Excellent. Good. Let me defer that to them. Yeah. Do you see that? Yeah. I'll wait then. I'll hold them back. If you've got a gap here, and you can see a lucent line here, I'll hold them back from impact stuff and bring them back for another x-ray. Yeah, so I'll wait on that. Because you can get a fracture there, and patients can misbehave. And I've seen fractures. I think everybody's seen fractures. So I file them more frequently and hold them back. Do you go back? If it's more than, if it's approaching six months, then I'll bone graft it. And I've had to do maybe five bone grafts over the year. So sometimes you do. Yep. And then you may have to retighten the screws or add a screw or whatever, but bone graft it. Yeah, and that'll generally work. Check their vitamin D. Some of these kids are like 12. You know, you got to fix that or it's not going to heal. But yeah. OK. So what a trochleoplasty can't fix, all right? Because I think trochleoplasty gets a little oversold. Potentially, we have to have really good indications to understand it. So here's another patient. Big prominence, you see. I hope you recognize that now. You can recognize on the lateral. That's way anterior to the femoral shaft. Post-trochleoplasty, I thought I did a great job. I was so proud of this case. I thought that looked gorgeous. Before and after. And look at those x-rays up top. Look at my post-troch, I love this case. I was so proud of this. This girl was happy. It was bilateral. And then she came back three years later. And she's got a J-sign again. She's got a jumping J-sign. Like, what the heck? And it gradually developed. OK, so this is a vector that's pulling that patella over. And eventually, it overcame the reconstruction, the NPFL. So looking at all the things we can measure, she's got valgus, 7 degrees. More than 6 is my trigger to say, that's important. Maybe I got to do something here. So 7 degrees of valgus is significant. She's got malalignment with the TTG and a big PTLTR way over the side. And this is post-trochleoplasty. So you see at the top, crazy anatomy for that trochlea. At the bottom, it looks gorgeous. But the patella tendon is sitting over the side, so the vector is terrible. So that's a combination of the valgus plus a lateralized tubercle that's creating a bad vector. So this has got to be fixed. So I pulled out all the stops on this girl. I did a DFO, opening wedge. I moved the tubercle over. I wasn't going to have her come back a third time. That'd be the worst, right? And then redo the NPFL, because you've changed the length of everything when you've changed the anatomy, the bony anatomy. You've got to do the NPFL over. Plus, she was getting a jumping J sign. She wasn't dislocating, but that would, I'm sure, be just a matter of time. So this highlights for me that you don't really create depth. I mean, you may improve the congruity, but up at the top, the patella dislocates in that first few degrees of flexion. And it's basically flat there, which is OK if you balance it. But you're not going to create enough depth that you capture the patella, and it can't overcome a bad vector. So you've got to change the vector, too. So my take-home message, I think I've covered it pretty well. Alt is important, and dysplasia. They really work together to create a problem. Jumping J sign tells you there's a lot going on. You need to do more. And think about vectors. Flat's OK. Convex is the issue. Any questions before I give it to the next speaker? Yeah. If you haven't talked to anybody, nobody's ever talked to about, are you guys, does that make it a correction? Are you lengthening them laterally? Potentially. So the question's about a lateral release, or lateral lengthening, or does he lengthening, as you alluded to. Yes. Of course, that doesn't solve the problem. I think everybody in the room, I hope, knows that. It's just basically to balance things at the end. So at the end of the case, I'll assess the lateral side. And if it's tight, I'll do a lengthening. Most of the time, if I'm distalizing the tubercle, I have to do a lengthening. If I have to move the tubercle a long way medially, most of the time I have to do a lengthening. But it's not a given. And so you don't see that focused here, probably for many of the presenters, because it's kind of just a balancing thing at the end. If you can't reliably tell where that patella needs to sit in order to fix your MPFL graft, then you may have to do the lateral lengthening before. Try not to, because if it's lengthened before, it can be hard to tell if you've over medialized it. And that is the easiest mistake for me to make, is to make the MPFL graft too tight in the patella medially. And patients don't like that. Yeah. Can you speak, when you do these combinations of the DFO plus the TTO, which one are you doing first? And how do you assess how much to move your tibial tubercle just because it's a moving target when you're not thinking about it? I don't. I do them in combination like this. This is a big hit. So just for practical purposes, I'll do the TTO, the DFO, and the MPFL last. MPFL has to be last after you've corrected the anatomy. So I'm still using the same threshold. So maybe I'm moving it even more, because when you swing the leg over with the DFO, that's moving the tubercle too. I don't have a way to do all that math. But yeah. That's why I was saying, I can't rely on your intraoperative. So I see that the intraoperative DTTG is what matters most, not the numbers in these cases. Because when you're moving the femur and the tibia, you're correcting in both planes. I think you have to just more rely on feeling the trochlea, feeling the tubercle, and watching the tracking intraoperatively. So take it up to 90. See if it sits underneath the patella. Fix it there. So you would do the DFO first, then the tubercle? I haven't. I've done the TTO first. But in general, there were times where I overcorrected. And I shifted it back a little bit. And I just look at the tracking at the end. Because I think, again, your numbers go out the window when you're moving both the tibia and the femur. So it's more important to check tracking on those cases. I know there's been a couple of papers that show that if you do a DFO, you move the tubercle 6 to 9 millimeters. So that may be one way to balance that in your math.

moving apprehension test

instability

patella

flexion

skeletally immature patient

trochleoplasty

anatomic risk factors