the session disclosures, none relative to this topic. So a patella does not just randomly dislocate and it doesn't start with a poor MPFL. There are anatomic risk factors in play and it's very important that you understand why each patella dislocates and measure and really assess your anatomic risk factors in every case. The solution is not just to pull harder with a bigger graft and then make an educated decision. So I'm gonna address when the femur's in play. So first, if you have any suggestion that there's excessive valgus as you examine a patient, get longstanding films. Many times I've been surprised once I radiographically quantify this. More than six degrees of valgus or mechanical axis that passes more than 50% in the lateral compartment is my threshold to consider correcting valgus. We don't have good prospective studies, only case series, but this is a uniformly accepted threshold, it seems, with the studies that we do have. You can do the lateral distal femoral angle to ensure that it is actually the deformity in the femur, which it almost always is. And if there's more than 12 months of growth remaining, tethered FICs or tethered growth can work very, very well. You can do it on the femur and or the tibia and correct it quite effectively, but if growth is finished, we need to think about correcting alignment and that would be with an opening wedge distal femoral osteotomy or also closing wedge on the medial side, which would cause more of a growth, or rather a leg length difference. So typically we're gonna do this on the lateral side. This is gonna indirectly improve your TTTG by seven to 10 millimeters when you correct a normal alignment, which we're gonna shoot for the weight-bearing axis 62% into the medial compartment, so slightly into the medial compartment, and you can plan your correction. So how do you do this practically? You're gonna do an MPFL with this case. So typically I will attach my MPFL graph to the patella and then I'm gonna pick the attachment site on the femur. I'm gonna do this radiographically, check isometry, and then place my pin angling slightly up and away from where I anticipate the screws to be in the distal femur, and then we're gonna make the cut over two parallel pins. Make sure your leg is flat on the table when you place the pins. If you have it up on a bolster, you will make this cut in flexion to give them a flexion contracture that they cannot overcome. Cut across the femur. You're well above the planned femoral tunnel for your MPFL. Then you can gradually distract while preserving that medial hinge, and then I encourage you to use a femoral head allograft that you can cut as a wedge. I didn't do a very good job cutting this one, but you get the point. It holds it open, frees up that space, and then you can place your plate and screws on that side of the knee, and I leave the nitinol guide wire with my shuttle suture in the femoral tunnel for the MPFL. If the drill bits or sutures tickle that, I see it, it's not too late, it's not my graft, and I can adjust accordingly with length of the screw, and then the last thing I'm gonna do is pull the MPFL graft into the femur and fix it, and that helps you avoid problems with collision of the screws and the MPFL tunnel. That technique I found to work pretty well. So rotation. Rotation's the next issue that comes up with the femur. This is something that we rarely have to address. Few surgeons have extensive experience with it. The threshold for most people, and myself, seems to be around 35 to 40 degrees of anteversion. How do you determine somebody may have too much anteversion? If you put them prone and internally rotate the hips, if they go all the way down to the table, that's a lot. You probably need to get a CT scan of the hip and the knee to assess it, or if there's more than 30 degrees of excess anteversion of internal versus external rotation when prone, that would be a trigger to consider getting a radiographic assessment. You may need to do a compensatory tubercle osteotomy after you rotate the femur, because you're also pulling the tubercle out with that. The other thing you may see this in is flexion instability. Now, this rarely comes along, but is a really challenging problem. So this is upside down. This is the exact opposite of a patella. It dislocates in extension. As you flex the knee, this goes out. This patient's under anesthesia, and you can see you have to hold it in, and it just goes right back out. That's generally a problem of valgus and or rotation. It's a short lateral column and an exceedingly tight extensor mechanism, and often the entire lateral complex is exceedingly tight. This usually requires a DFO and a very extensive lateral release. Now, I do lateral lengthenings across the board. I try to preserve the lateral tissue, but you can't lengthen this and repair it. There's not enough tissue, so typically you have to use a patch, one of the dermal allograft patch, such as what we use for rotator cuffs on occasionally, can work well so that you have something to contain the effusion on that side, and it's not unbalanced. You often have to do something to the quad. There's no better case. It drives home the point of thinking about this problem of patellofemoral instability as a vector problem. These vectors are severely pulled laterally, and you typically have to release the vasolateralis, attach it more distally, and sometimes do a VY lengthening of the whole extensor mechanism. If you have rotational problems as well, you can do a biplanar osteotomy. This is a complex topic. I direct your writings by Imhoff. He's had a couple of papers. The math is kind of complex, but you basically cut this bone at an angle and then rotate it, and because it's at an angle, you'll correct both valgus and rotation with this using a two-plane external fixture, as you see here, placing K wires at the desired amount of correction and then rotating until they're parallel as a way to do it. The two-plane fixture really helps you control this otherwise floppy construct until you get the plate and screws on there. So now getting to dysplasia. So this is another subset with the femur. So first you gotta recognize it, and that's done on the lateral x-ray. If you see where the blue line and the red line cross, that's your crossing sign. That's where the depth of the trochlear groove meets the height of the lateral trochlear ridge. If it extends further anterior, that's a bump or supratrochlear spur. That's further anterior to the cortex of the femur. You know that you need three-dimensional imaging then. It's not about flatness. This is the same knee, 45 degrees of flexion, and a full extension. You see this convex bump and the patella teetering on it. You know that's a problem there. For me, it's about the convex shape, most of all. It's not about flatness. Flat on flat can absolutely be balanced. It's not about flatness. That problem does not need a trochlearplasty for my patients. But when you see a spur, I wanna quantify it. How big is that? Draw a line down the anterior femur. How much sits in front of the femur on that view at the notch? This should be flush. This is where the cruciates are. This should be the lowest part of the trochlear groove. So all that's prominent. And you get these patients, it's a very small subset, that have very unusual anatomy with this prominent convex shape, and you're not gonna solve that problem with a soft tissue procedure. We're gonna need to drop that down flush with the anterior femoral cortex, like that cartoon there. This is a very small subset of people. The de Jure classification is really descriptive. And if we get caught up in this and what classification, we're gonna probably be misguided in our treatment decisions. The A, excuse me, the Bs and the Ds are the ones we can correct. But this is really just a shape. It's not guiding our treatment choices. It's more about the convexity. And then what do you see on exam? You'll typically see a jumping J sign as we heard Elizabeth talk about. So this view arthroscopically is from above. This is a hugely prominent spur. That should be flush with the femoral cortex. You see the chondrosis that you're getting. And on the right, you see the exam that this person, every time they extend their knee, it jumps over to the side. That is problematic. That is a combination of a convex shape plus a bad vector. The two are going together and we can't forget that. You have to correct both of these. So my indication is to consider deepening trochleoplasty or type Bs or Ds in terms of the shape. But really that convex shape of the trochlea, a large spur greater than seven millimeters and that J sign on exam is really helpful. Especially in the setting of patella alta. If you have significant patella alta, CD ratio greater than 1.4, it's gonna make every other anatomic risk factor more pronounced in its effect. So you need to be thinking about it then, especially with revisions and I'm always doing an empty patella with it. Now here, the point about patella alta, if you have that plus dysplasia, it's a very bad combination. So here's a patient with really poor mechanics. You see that this patella tendon is completely draped over the side. Their CD ratio is 1.5, which is quite high. So there is an opportunity when they start that high to just move them distal. So in this case, I worked around the dysplasia, moved them down 12 millimeters, over 13 millimeters. Now the patella's actually past that spur, trochleoplasty's not needed. This would not work, however, if you have a convex trochlea where this patella would end up. So you can't correct everything by moving distal. Here's a patient who had a well done operation with a tubercle osteotomy and MPFL and corrected all these variables, moved it way over, way down, and look at that patella trochlear overlap. It looks fantastic. These numbers look great. They have some valgus, but they still have pronounced jumping J sign and their patella would get stuck as they tried to extend their knee because they have this convex, very large spur. So that was still, because of that shape where the patella rests, that person still needed a trochleoplasty. When we got in there, it was actually even taller. It was 14 millimeters. That's huge sitting in front of the femoral shaft. Dropped it down flush with the femoral shaft, changed the shape, and that's what that patient needed with a revision MPFL. Two ways to do it. Thick shell, which is what I do and learn from DeJure. Thin flap results in a thinner construct. Both of these techniques fix it with absorbable suture and absorbable anchors, and we really don't know which is better. My concerns are, I don't want to have chondromacrosis from heat if I make this flap too thin, but I really don't think we know which one is better. So here's a video of the technique. So this is a convex shape up top. You can see this was about 12 millimeters sitting in front of the femoral cortex, and then there's a little bit of art to planning this, but we're gonna try to create the new groove, the depth of the new groove, going up the femoral shaft to create the normal anatomic axis in line of pull with the quadriceps. So then we'll look at where the convexity changes on either side from going up to down. You see that's where the dotted line changes, and then we're gonna first take out a wedge of bone all the way around the edge, encroach slightly upon the articular cartilage so that when you're done, it's gonna actually sit flush. Take that bone out, mince it up and save it for the end of the case. And we start a cavity this way, flush with the anterior femoral cortex, then come in with a burr to start to remove the bone. This is a three millimeter burr. You can do it all with the next tool I'll show you, but it takes a long time because this moves at a drill speed rather than a burr speed. So I'll typically start with that high speed burr and then come up with this offset guide. I have no relationship with this company, but I think this tool does add a measure of safety. I only use the five millimeter offset, so I'm left with a five millimeter composite cartilage plus bone shell that I'm then gonna osteotomize. You need to use this like a windshield wiper. We wanna use it side to side like every other tool we use with a burr, but it really is not aggressive enough to remove the bone. You have to pivot around a point. Then I'll take a 20 blade and a bone tamp and crease it right down where I want this thing to bend. And usually up on the lateral side, you have to do the same. You almost never have to do it on the medial side. It's flexible enough. And then you can reshape it with your finger. Now I'm gonna take some of that minced bone and I'm gonna pack it into any voids. You're gonna have some irregularities underneath and also around the edges to give it some lift. It's not so much about recreating depth. It's about getting rid of this convex shape that's sitting anterior to the femur. The vicral sutures hold it in place. Tap in, knotless suture anchors can hold it in place there. And you see that the convex shape is gone. You get some depth, but again, this is not an operation for containment. The cartilage tolerates the vicral sutures very nicely. They dissolve in six to eight weeks and it heals readily. But this is probably the most important slide, okay? So a trochleoplasty can't fix a lateral vector. If the patella's sitting over the side, regardless of the shape, a trochleoplasty alone is not gonna create enough depth to magically hold that patella in place. There is a vector that's pulling that patella sideways. In this case, probably highlights it better than any. Three years out from a trochleoplasty, you see the pre and the post sunrise view. This looks really good. But look what happens at three years. This person gradually developed this recurring J sign. They weren't dislocating, but clearly this is not a good outcome. So if you look at their numbers, this person had valgus that was not corrected, malalignment that was not corrected, a very high PTLTR. I encourage you to use this number. It's very, very helpful because it reflects how much patella tendon is sitting draped over the corner. I'm sure Liza's gonna look at this too in her next talk. But this was uncorrected. But look, a very nice deepening trochleoplasty. That looks fantastic, but you saw the outcome. So that needs to be corrected too, and that's done with the DFO, and in this case, the tuberculoplasty too, because you didn't want to take any chances in a revision MPFL. So take home message, patella alta plus dysplasia, you need to think about doing something more than MPFL. Jumping J sign definitely needs something more than MPFL, as we heard in the last session. Flexion instability, very unusual. Aggressive lateral lengthening, and you gotta change that vector, generally with a DFO. A flat spur may benefit from a trochleoplasty, remains to be determined, but it's really a very small number of people with a convex trochlea that need this. We did an ICL yesterday. I'll just share this perspective. David DeJour probably has more experience than anybody on the planet with trochleoplasty. Incredible referral practice, he does 35 a year. In the US, I probably have as much experience as anybody. I do maybe 20 a year, and I'm doing five or six patella instability cases a week. Huge referral practice. So it's a very small subset that need this. I hope this talk helps people identify maybe that subset that do need it. Thank you.

anatomic risk factors

patellofemoral instability

valgus correction

trochleoplasty

surgical techniques