My disclosures, so trochlear dysplasia, as we've seen, has become recognized as one of the key anatomic risk factors for recurrent patellar instability. Here's a systematic review on 17 studies that showed that this bubbled up as the most important anatomic risk factor for recurrent instability. But probably more important to recognize is that the combination of risk factors, it really is more important. And as you get to three anatomic risk factors together, your risk of recurrent instability is approaching 80%. The first thing we have to do is recognize dysplasia. This is done from a lateral x-ray. We look for the base of the trochlear groove, which is a blue dashed line, as you exit Blumaset's line and move anteriorly and superiorly. Where this crosses the red dashed line, which is the height of the lateral femoral condyle, they're at the same level, so it's flat. That's called the crossing sign. It's flat from that point moving proximal in the trochlea. As you go further superior, if it extends anterior to the femoral cortex, the green dots, that is a supratrochlear spur. So when I see this on a lateral x-ray, I know I need three-dimensional imaging to better understand and eventually quantify this. So I'm going to get an MRI. It is not about flatness on your Merchant or Sunrise View x-ray. I learned very little about the trochlear morphology from the Merchant View. This is the same knee, 45 degrees of flexion. And full extension. And you see this convex supratrochlear spur with a patella teetering on it. And that's the pathoanatomy that I'm looking to change with a deepening trochleoplasty. Again, this is the same knee. I learned very little from that Merchant View. The convexity, I think, is a key concept. Flat trochleas do not need a deepening trochleoplasty. Flat on flat can be balanced and have a good outcome, generally with an MPFL reconstruction alone, as you see there on the left. Especially if they have good cartilage overlap, as you see with the patella trochlear index, in this case, greater than 50%. But it's these convex supratrochlear spurs that have profound influence on the patella. And the patella, as you see, is just teetering and can go either direction. So we still have to decide whether this trochlea truly influences patella trackling. So I'm going to quantify the dysplasia. It's not merely the presence of dysplasia. I'm going to go to the sagittal cut of the MRI. So here we are at the notch. That should be the deepest part of the trochlear groove. As you extend approximately, that should be flush with the anterior femoral cortex in a normal knee, which is that yellow line. Everything that extends anterior to that, bone plus cartilage, is the supratrochlear spur. And I will measure this. For me, greater than seven millimeters of bone plus cartilage gets my attention as possibly needing a deepening trochleoplasty. If I couple this with a convex shape, as you see here, that's my indication. I'm also going to see whether this actually influences patella tracking on exam. David Dujour gave us a very nice descriptive classification, but it doesn't really guide treatment. These are Bs and Ds that have the supratrochlear spur that we have the opportunity to correct by dropping down flat to the femoral cortex. The Cs don't have a supratrochlear spur. They just have dysplastic anatomy with a hypoplastic medial facet, which is also present in the Ds. But this doesn't really guide treatment decisions. I'm going to look at the exam. How does the spur influence tracking? This jumping J sign exam that you see here is evidence of a spur that really has profound impact on the patella. On the bottom left, you see an arthroscopic view from above, from a superior lateral portal. And you see how this is a jumping J sign viewed arthroscopically. And look at the chondrosis already present in this 19-year-old and how this thing jumps as the knee is flexed. And also appreciate how much bone and cartilage is sitting anterior to the femoral cortex. That should all be flush with the anterior femur there. So the J sign, what's happening with the J sign? The patella is completely leaving any bony constraint in full extension and then finding the groove as you flex. This is due to either patella alta sitting completely above any engagement with a groove whatsoever or dysplasia or both. And I would submit that the combination is especially important and really important to recognize because any trochlear dysplasia with the presence of alta, that patella has to navigate past that dysplasia every time the knee bends. So I'm going to carefully measure patella alta on all of my patients. I'm going to measure the CD index and the patella trochlear index because a short trochlea can behave just the same as a high-riding patella. It's a lack of overlap and the knee has to flex further till that patella engages a more normal groove. And then next I'm going to say, well, maybe kind of work around the dysplasia. If I have enough patella alta that I can normalize that patella height by moving it distally and get closer to a more normal groove or even a flat groove, that can be very successful. Here's a patient with a supratrochlear spur dysplasia. The patella sits way lateral, but that's way high. 1.5 for a CD ratio is extremely high. No overlap with the patella trochlear index of zero. And I moved this patient, they were malaligned as well, I moved them down and over, trochleoplasty not needed. I could work around it. So what's different about this patient? This is a patient sent to me, had surgery done very well, had failed a TTO and an NPFL years ago. The alignment and the patella height had been corrected quite well. And here you see their numbers now. Great overlap with the cartilage, a little bit of valgus, but still a pronounced J sign and they could not actively extend the knee. The patella would get caught with an extensor lag as they tried to actively extend due to the way it's just malaligned and that spur is engaging with the patella. And the difference here is this large convex type D spur that measured nine millimeters on the MRI. So when you have the presence of this large convex spur where the patella has to ride after you've corrected ALTA, that's not, it could be successful with a workaround procedure. This person needed a trochleoplasty and here in the OR that actually measured 14 millimeters. It was quite large and this is after dropping it down to flush. So my goal is to make the trochlear groove flush with the anterior femoral cortex. I do try to achieve some depth, but it's mostly about dropping that spur down to flush. So my decision making, I'm always doing an NPFL reconstruction with these patients. I'm considering a trochleoplasty with type B's or D's and a convex trochlear greater than seven millimeters and especially with a jumping JSON on exam and in the presence of ALTA or for revision procedures. There are two basic ways to do this. I'm going to show you the thick shell technique, which I learned from David DeJure. I'm going to create a three to five millimeter shell of bone plus cartilage and then osteoidomize it and reshape it. There's also a thin flap technique that Dr. Schottel has popularized that thins it out even further until it's malleable and then it is reshaped but not osteoidomized. Both of these hold this in position with absorbable sutures. So here we are in the OR. This is an osteotome. The proximal is at the top of the screen and you can see this is about a 12 millimeter spur of bone plus cartilage sitting anterior to the femoral cortex. I've reflected the synovium, peeled it back so that I can see the femoral cortex there and I'm going to plan my osteotomy and mark it out. That blue line is down the femoral shaft and that's going to be the distal extent of my shell. So almost all of these patients have an existing groove that is directed abnormally medially, which makes it even harder for the patella to get into that groove. So we will typically lateralize the new groove directly up the femoral shaft, which you see that single dot up there at the top. How far distal I go with this is going to be basically where the intersection is of the femoral, anterofemoral cortex. If you extrapolate that distally to where it goes and intersects the articular cartilage, that's that horizontal line I just drew. And then now this is my planned new groove, which will improve the TTDG because it's going to be lateralized and it's going up the femoral shaft. Again, the extent distal is where it intersects with the anterofemoral cortex. Now the transition on the medial lateral side is where, where basically the curve changes shape from going up to going down if you look at it from the lateral side. And the apex of that convexity is distal margin of my correction. Now I'm going to start by removing a wedge of bone with an osseotome. This starts flush with the anterofemoral cortex, and I come all the way around, and it's important to start slightly onto the articular cartilage here in order to allow you to drop it fully down flush. I'm going to take this wedge of bone out. I'm going to mince it up and save it for the end of the case. Now you see that cavity has begun. Notice I started on the cartilage. Then I begin with a TPS instrument and a three millimeter egg bur just to get this started to create the cavity. This is a very aggressive instrument. Save the slurry again for later when we're going to fill the voids. Now this is a commercially available guide. I have no relationship with this company, but I do think this guide offers a measure of safety and reproducibility for this procedure. I do think it's helpful. I use the five millimeter offset only. That's the thick shell technique, and I know exactly where the tip of that is. You want to use it, your hands want to use it side to side, but it's not aggressive enough. It's on a drill, so you have to use the windshield wiper technique that you see here, and when I do this all around underneath this shell, I know I've got a five millimeter thick combination shell of bone plus cartilage. This is the windshield wiper method. If you try to start the procedure with this, it just takes a lot of time. That's why I begin with the TPS bur to begin the cavity. Now this bounces like a diving board, and I'm going to take a 20 blade with a bone tamp, and I'm going to osteotomize the center of the new groove. I place the osteotome behind it to control the amount of deflection so it doesn't crack in an unanticipated way that you can see there. Now it's malleable, and then on the lateral side, I'll do the same thing just at the ridge. You don't have to go any further than that. Now it's very malleable, and I can reshape it. Almost never do you have to do that on the medial side. It's always supple enough, and then I'm going to take that slurry and those little bone chips. I'm going to pack it underneath and fill any voids or irregularities. I can palpate with a freer elevator, and then take the chips and pack it along the margins to provide a little bit of depth when I'm done. It's especially important to pack some of the cartilage right at the corner where the cavity starts, and I'm going to fix all of this with absorbable tap-in suture anchors and two number two vicryl sutures, two in case one breaks, and I'm going to bring a pair of limbs of this suture up over each shingle to hold it in position, and you can titrate where you want this to be in order to reshape these two shingles. Tap it in here until tight, but not overtight, and these vicryl sutures are very well tolerated by the cartilage. You can see on the medial side, I didn't have to crack it at all. Small crack up on the lateral side, and I can adjust where I put this to the way it's going to reshape that new trochlea just like that. And now that's flush with the antefemoral cortex, you can see my freer on the femoral cortex coming down to the shaft, and there's a view from the side. That spur is completely gone, it's flush with the front of the femur, and I have provided some lift, but again, my primary goal is to be flush there. Then I'll take the free ends of these sutures with a free needle and pass it through that synovium and tie it down, careful not to grab too much tissue or it'll encroach upon the articular cartilage. The cartilage tolerates the absorbable sutures quite well as you see here on three different patients with second looks. It's important for these patients to move immediately, otherwise that raw cancellous bone is ripe for scar tissue to form, and you can get very dense scar tissue. So immediate motion is very important. I brace them for six weeks, partial weight bearing, and really then progress is tolerated, and this bone heals very rapidly. We published our results last year in the Arthroscopy Journal, which you can see here, and half of these patients were revision patients, so it's a tough population, but they did quite well. So here's my take-home message. It's important to recognize if you have patella alta plus dysplasia, you need to do something more than an MPFL. Often correcting the alta is sufficient. If you've got a jumping J sign, you also need to do something more than actually an MPFL, and correct the alta enough to engage a flat to normal groove, and often that's going to solve this problem. Flat prominent spurs may benefit from trochleoplasty. I do not do this for the indication of pain, but a convex trochlea needs a trochleoplasty. Thank you.

trochlear dysplasia

recurrent patellar instability

trochleoplasty

patellar tracking

supratrochlear spur