The immature patient with patellar instability, this is a pretty common patient. There's some things that are a little bit less common. Here are my disclosures. So this girl is 13, premenarchal, and her first dislocation was in kindergarten. But impressively, she's a three-sport athlete, volleyball, softball, and basketball. And when you ask how many dislocations she's had, she and her mom say it's been innumerable. So on physical exam, first of all, there was apprehension. And at least I put a lot of stock in apprehension. I think it's pretty rare that you see a patient with patellar instability who does not have apprehension. It happens. But I do see patients come in where they're playing soccer, and something happened, and the athletic trainer in high school says, you know, you dislocated your patella, so the patient just has it in their head. And when you actually, well, examine their knee, they might have done something completely different. So that's the ACL. It's a similar mechanism. But this girl had no endpoint to lateral translation. She had a jumping J-sign. There was a small effusion. But she did have full range of motion, and her Baten score was 5. So I do look at Baten score in all patients with patellar instability. Katam Deschamps measured 1.49, so you can see here, if you're not familiar with measuring it, you typically look at the slice where you see the ACL. In this particular case, if you look at the slice with the ACL on the right, you don't see the patella. So you scroll over laterally until you actually see the articular surface of the patella. I think it's a little bit less of an accurate measurement in patients who have significant lateral subluxation of their patella. But here, it measured 1.49. There's another measurement called patellar trochlear index. If anything, I put more stock in this because there are patients with a much longer trochlea, so they have more overlap, and then there's other patients with a short trochlea. And it's all about engagement. If the patella is not engaging in the trochlea, the risk of, in my opinion, redislocation is much higher. So this measured 22%. And basically, this is just a study looking at that. But I usually don't get my calculator out. I just kind of look at a rough estimate. And then TTTG. So if you look at her axial cut, how you measure is you just put your cursor at the center of the patellar tendon insertion on the tubercle and you scroll up. And MRI generally has been shown to underestimate compared to CT. I do not get a CT in my patients unless I'm really concerned about their lower extremity version. But just be aware, like the old number of 20 may be a little bit lower when you look at MRI. Lastly, measuring sagittal TTTG. I do not measure this in all my patients, but basically it's looking at how anterior or how posterior the tibial tubercle is. So she had a very lateralized tubercle. It measured 25.2. Patellar tendon lateral trochlear ridge, another measurement that I don't typically measure, but I think it's something that you can just eyeball if you're scrolling up and the tendon is really sitting far laterally like in this case. This was one of our co-workers at HSS, Pete Fabrikant and Mistovich published a study in 2018 and basically showed that instability patients had a significantly higher number here, 9 millimeters versus 2 millimeters. And it was quite sensitive and even more specific for instability. And lastly, trochlear dysplasia. So again, I don't look at whether it's a B or a D. I just look whether or not they're dysplastic. The lateral X-ray is better than the merchant view, but certainly you can see on MRI. So what are the issues in this girl? She's got patella alta, she's got trochlear dysplasia, she has a lateralized tibial tubercle. And what are the options? Well, a brace. I tell patients that's like catching a slippery fish and she's already been trying every non-operative modality for seven or eight years. Physical therapy, MPFL, MPFL plus shorten the patellar tendon, which I think maybe Jason is going to talk about. And the historic options such as a root goal weight and a Hauser are not particularly great operations. You can see this MRI. This was a root goal weight where you see on that axial cut routing the lateral aspect or the lateral third of the patellar tendon under the patellar tendon and then attaching it more proximally and more posteriorly on the tibia. This is not an operation that I do at this point. There's a number of studies saying that MPFL reconstruction in isolation can be quite effective. The first study here looked at 52 patients with chronic instability and found no significant correlation between the collected risk factors and post-operative outcome scores. Beth Schubenstein published a study looking at 72 patients with chronic instability, no cartilage defect or significant pain, and had a low re-dislocation instability rate. And it was regardless of bony pathologies, including TTTG, Catan, Deschamps, and trochlear dysplasia. However, in this patient I didn't have any choice. She's skeletally mature. So I used all suture anchors on her patella and an all suture but larger suture anchor in her femur. I used a gracilis allograft. My preference is allograft over autograft. I fixed her in 30 degrees of flexion, careful not to over-constrain her knee. And certainly she had improved alignment post-operatively. But 19 months post-op she had a re-dislocation playing softball. And I wasn't surprised and the family wasn't surprised because I had warned them that based on her anatomy and age and level of sport that this was going to be a significant possibility. They read the MRIs and attenuated femoral attachment. But at this point now her bone age was 16. You can see on Merchant now she has significant lateral subluxation. And the revision in this case was an AMZ with a distalization. And when you do this, when you have a patient re-dislocate, you do have to redo in almost all cases the MPFL. Because first of all, she's grown. Her alignment has changed. And this was with the lateral lengthening. So sometimes you can get away without a lateral lengthening in patients like this. It really depends on how lax that lateral capsule is. Despite the fact that she had a Baten score of 5, I could not avert her to neutral. I personally use a tightrope for femoral fixation in most cases. And here you can see an Evans wedge for the distalization. So you can see her alignment significantly improved. So the factors to consider is consider, I'm not saying to do a distalization, but consider it when the catom de champ is above 1.2. And then it really gets down, at least for me, it's all about overlap. Look at trochlear dysplasia. If there's a cartilage injury in the inferior aspect of the patella, that may be a reason to consider an osteotomy. Look at the TTTG and where the patella is actually sitting and where the patellar tendon is sitting. And then of course take a look at skeletal maturity. But if you look at a patient like with this photo, of course you're going to get an MRI, but you can see a significant lateralization of the tibial tubercle. And just some images, you can see here some significant fat patedema. This just should put it on your radar that you may want to consider a distalization here. All the cartilage wear is inferior third of the patella. We'd like to unload that. Significant translation. And just, you see a Merchant View like this, you're probably not going to get away with an MPFL. And take a look at the FICEs. I'm always using fluoro in these cases when they're skeletally immature just to make sure that I'm below the FICEs. Thank you very much. Any questions? Go ahead. Why did you need the Evans wedge for the distalization? So I started using allograft bone approximately maybe about eight or nine years ago just to give it a buttress. And then we've subsequently done a biomechanics study with and without a wedge, and it does add significant stability as far as load to failure. The other aspect of it is it's very reliable, meaning there's different sizes. So it's just very accurate as far as measuring how far you're actually distalizing. And so it's not that everyone gets a 10. Sometimes in a tiny patient, they may have an eight wedge. Some people get a 12. It really depends on what I measure preoperatively as far as what I use. Where are you putting it? Because if you're not interiorizing, so if you're distalizing, I guess I don't understand where the wedge would go. So I typically am anteriorizing. So here it was a distalizing AMZ, which you can see the distal aspect is—unfortunately, I don't know why they have so many lights. But anyway, so it's anterior medializing and distalizing. And the other technical aspect is aiming the screws distally. It also increases the load to failure as opposed to just going parallel to the osteotomy. And you can use autograft as well. So when I do this, I just take the segment out that I've used. So I'm actually taking the osteotomy segment from below that I'm distalizing, and I just take that and move it proximally. And that works just the same way as a buttress. Any other questions? For both of you, as you distalize, will you always do a step cut and remove that bone? Or will you sometimes do an overlap if you're distalizing less? I'm a step cut person. You're a step cut? I never step cut. I say I feather it. So I think it looks less scary to me on x-ray. When you watch that distal aspect, it takes a little while to heal. So feathering it—I still take off bone distally, but it's, I think, a little bit less of a cortical defect or maybe just looks less scary on x-ray. Yeah, go ahead. When you're determining how far to distalize in the setting of severe dysplasia, are you just going off of your autonomous shots? Or are you taking into account, like, their dysplasia and trying to bypass that kind of curved jump type thing? Both. So I'm looking at Katamda Shamp, but then in these patients with a shorter trochlea with less overlap, I might be more likely to distalize a little bit more. And patients who have, you know, let's say this patient had 20% overlap. I want to get her down because of her dysplasia, but I'm a little bit less worried about it. But in those patients, it's 5%. And so those patients, depending on what the measurement is, I kind of adjust it to distalize a little bit more. For your grout fixation for the APFL, how do you tension on the patellar side? Do you use anchors? How do you get that tension correct if you're dogging it on the femur first? So I prefer to do it the other way, but in skeletally mature patients, I like to not use a screw. So I basically fix the femur first, but I've already put my sutures and my suture anchors on the patella. So that means that I check isometry when I'm looking for my femoral point of fixation. So the first thing I do is put the anchors on the patella, then I put a guide pin in the femur, I check isometry, I fix it to the femur, and then I bring both ends up. And I basically tie each end to one of the anchors with just a surgeon's knot, make sure that they have full range of motion, feel it, and then secure it down. So while I fix it in 30 degrees, I still want there to be a little bit of play. And last question, is there ever a circumstance, you mentioned, in these revision settings usually needing to revise the MPFL, if it's a skeletally mature patient and it seems like the MPFL was in the anatomic position, but there are other times where that's not needed, how do you know? Typically that would be the case where you're doing an osteotomy not for recurrent instability, you're just doing the osteotomy for a cartilage issue and pain. So I would say if they continue to dislocate, I can't think of a patient that I haven't had to revise. The other thing that's nice, I think, about all suture anchors is you're not worrying about the bone and the patella. Obviously it's a little bone. In most revision situations, I end up doing more of an MQTFL, and so it's a little bit different, actually, technically. Thanks. That was a great case.

patellar instability

MPFL reconstruction

redislocation

AMZ procedure

distalization